Selasa, 20 September 2011

GMR-Giant MagnetoResistance

Detection of nanoscale ESD effect on GMR head signal using the wavelet transform technique: HBM and CDM cases Original Research Article
Journal of Electrostatics, Volume 67, Issue 4, July 2009, Pages 583-589
N. Suwannata, P. Rakpongsiri, D. Sompongse, A. Siritaratiwat
An electrical signal anomaly is an undesired signal and is difficult to detect by a commercial instrument due to its short duration and unpredictable fault on a signal. Since a GMR recording head is a stack of nanometer thick multilayers, in particular, a magnetic layer and conductor layers, for magnetic insulating spacers, it is very sensitive to electron movements. Visible damage is understandable and protectable but latent failure cannot be measured. It is possibly observed by using frequency-domain apparatus but certainly it is not real-time detection. Therefore, in order to detect a latent failure head affected by ESD in the time domain, current conventional instruments are ineffective. In this study, the wavelet transform technique using the 4th order Daubechies is proposed to detect the glitches on a magnetic recording head signal in the time domain. It is found that the glitches occur when the ESD level of the charged device model (CDM) and human body model (HBM) on giant magnetoresistive (GMR) heads are in ranges of 6–15 V and 40–120 V, respectively. The electrical test parameters and scanning electron microscope (SEM) photo of the recording heads show no visible change in reader sensor. To ensure the results, the GMR damage is observed by SEM when the CDM-ESD and HBM-ESD are 10 V and 130 V, respectively. The glitches in the magnetic response signal of the GMR head are found to increase when the ESD level is increased. Thus, the Daubechies wavelet transform technique can be a novel approach to detect the pre-degradation of a GMR head due to an ESD effect.
Keywords: ESD; Wavelet transform; GMR head; Glitch

Classification of pulsed eddy current GMR data on aircraft structures Original Research Article
NDT & E International, Volume 43, Issue 2, March 2010, Pages 141-144
Jaejoon Kim, Guang Yang, Lalita Udpa, Satish Udpa
This paper presents a technique to automatically detect third-layer cracks at rivet sites in aircraft structures using the response signals collected by giant magneto-resistive (GMR) sensors. The inspection system uses pulsed waveform as the excitation source of a multi-line coil and captures the transient fields associated with the induced eddy currents via a GMR sensor, which was developed to detect cracking and corrosion in multi-layer aircraft structures. An automatic scan of the region around the rivet generates C-scan image data that can be processed to detect cracks under the rivet head. Using a 2-D image of each rivet head, feature extraction and classification schemes based on principal component analysis and the k-means algorithm have been successfully developed to detect cracks of varying size located in the third layers at a depth of up to 10 mm below the surface.
Keywords: Giant magneto-resistive (GMR) sensor; Pulsed eddy current (PEC); Principal component analysis (PCA); k-means algorithm

Analytical compact modeling of GMR based current sensors: Application to power measurement at the IC level Original Research Article
Solid-State Electronics, Volume 54, Issue 12, December 2010, Pages 1606-1612
A. Roldán, C. Reig, M.D. Cubells-Beltrán, J.B. Roldán, D. Ramírez, S. Cardoso, P.P. Freitas
An analytical compact model for giant magnetoresistance (GMR) based current sensors has been developed. Different spin-valve based full Wheatstone bridge sensors, with the current straps integrated in the chip, have been considered. These devices have been experimentally characterized in order to extract the model parameters. In this respect, we have focused on the sensors linear operation regime. The model, which allows the individual description of the magnetoresistive elements, has been implemented in a circuit simulator by means of a behavioral description language: Verilog-A. We also propose the use of the devices in a direct power measurement application at the integrated circuit (IC) level, by taking advantage of their multiplicative properties. A simple circuit is suggested, and analyzed in depth by means of the tested model, showing promising results regarding the application range.
Keywords: GMR; Spin valve; Electrical current sensors; Integrated circuits; Electric power measurement; Wattmeter

A GMR–ECT based embedded solution for applications on PCB inspections Original Research Article
Sensors and Actuators A: Physical, Volume 167, Issue 1, May 2011, Pages 25-33
Matteo Cacciola, Giuseppe Megali, Diego Pellicanó, Francesco Carlo Morabito
Real-time non-destructive testing and evaluation (NDT/E) of conducting materials using eddy current techniques (ECTs) has gained significance in the last few years. This paper proposes a real-time application of ECT–NDT system exploiting giant magneto-resistive (GMR) sensors for inspection of printed circuit boards (PCBs). Probe design aims to crack inspection over flat surface, especially suitable for micro-defect detection on high density bare PCB. We propose a system based on a GMR sensor able to detect the magnetic field resulting from the interaction between a planar coil exciter and PCBs. The EC signals, detected by the GMR sensor, have been acquired by a high speed analog-to-digital (A/D) converter, for a subsequent application of signal processing based on digital techniques. The achieved results have highlighted the efficient design of the system. The advantages of the proposed models and some possible improvements of the system are also discussed.
Keywords: PCB; Crack detection; ECT; GMR; Magnetic sensors

Integrated GMR angle sensor for electrical commutated motors including features for safety critical applications Original Research Article
Procedia Engineering, Volume 5, 2010, Pages 1384-1387
Wolfgang Granig, Markus Weinberger, Christian Reidl, Manfred Bresch, Michael Strasser, Gerhard Pircher
An integrated GMR (Giant Magneto Resistance) angle sensor will be presented which is designed to fulfill requirements for electrical commutated motor-drives. These motors use sine-commutation for the coils and need the angle of the motor-shaft in accuracy ranges below 1∘ with update-rates of 50- 100 μs. This integrated GMR Angle sensor solves this problem using integrated GMR Angle-Sensors on top of the silicon signal processing chip. The differential GMR-bridge signals are converted to the digital domain by sigma-delta ADCs and these raw-signals are error-compensated. An additional autocalibration feature is implemented to improve the accuracy during operation. The very fast angle-measurement is performed using parallel analog signal processing, 24 MHz finite state machine with dedicated peripherals and an 8 Mbit/s SPI interface. An additional feature to reduce the time delay is the implemented angle-value prediction. Built-in selftests, switchable voltages for signal-path tests and multiple safety voltage comparators are implemented for safety-critical applications.
Keywords: GMR; Integrated GMR; Angle sensor; BLDC motors; EC motors; Motor commutation

CPP-GMR technology for magnetic read heads of future high-density recording systems Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 6, March 2009, Pages 508-511
Keiichi Nagasaka
This paper introduces CPP-GMR technology, its features, routes to output enhancement, problems to be solved and possibilities as a recording head. For instance, use of high spin-dependent bulk scattering, high resistivity, or half-metallic magnetic materials for free and reference magnetic layers were shown as ways to improve the output of CPP-GMR. A current state of CPP-GMR head development was also mentioned in view points of sensor downsizing, magnetic head noise and high-density recording demonstration. CPP-GMR still has some points to be improved, however it is believed that the CPP-GMR will actualize a next high-performance magnetic read head in no distant future.
Keywords: CPP-GMR; Magnetic read head; HDD

Effect of material selection and background impurity on interface property and resulted CIP-GMR performance Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 18, September 2009, Pages 2902-2910
Xilin Peng, Augusto Morrone, Konstantin Nikolaev, Mark Kief, Mark Ostrowski
In this paper, we investigated the effect of background base pressure, wafer-transferring time between process modules, and stack layer material selection on the current-in-plane giant magneto-resistive (CIP-GMR) interface properties and the resulted CIP-GMR performance. Experimental results showed that seed layer/AFM interface, AFM/pinned layer (PL) interface, pinned layer/Ru interface, and reference layer (RL)/Cu spacer interface are among the most critical ones for a CIP-GMR device. By reducing the background impurity level (water moisture and oxygen), optimizing the wafer process flow sequence, and careful stack-layer material selection, such critical interfaces in a CIP-GMR device can be preserved. Consequently, a much robust GMR performance control can be achieved.
Keywords: CIP-GMR; Interface; Lattice mismatch; Seed layer; AFM; SAF; TEM

Thermal stability of a Co/Cu giant magnetoresistance (GMR) multilayer system Original Research Article
Ultramicroscopy, Volume 109, Issue 5, April 2009, Pages 637-643
V. Vovk, G. Schmitz
Critical limitations exist regarding the thermal stability of multilayer giant magnetoresistance (GMR) sensors due to significant contribution of layer interfaces and grain boundaries to their performance. This paper addresses the stability of, and thermal reaction in Co/Cu magnetoresistive systems. Thin film multilayers were deposited by ion beam sputtering on top of preformed tungsten tips. The multilayers were then analyzed by a wide-angle tomographic atom probe (WATAP) in the as-prepared state and after heat treatments in the temperature range from 150 to 550 °C.
As revealed by the WATAP analysis, Co breakthroughs along grain boundaries in the Cu spacers appear at 450 °C. This morphological change leads to a deterioration of the GMR effect due to the magnetostatic ferromagnetic coupling between Co layers. Furthermore, a strong effect of Cu layers faceting is observed after annealing in the same temperature range, which may lead to the deterioration of the layered structure on high-angle grain boundaries.
Keywords: GMR; Thin films; wide-angle tomographic atom probe (WATAP)

Current-confined-path (CCP) giant magnetoresistive (GMR) sensors Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 12, June 2009, Pages 1889-1892
Xilin Peng, Paul Kolbo, Konstantin Nikolaev, Shawn Chen, Zhongyan Wang, Tom Boonstra, Paul Anderson, Steven Kalderon, Peter Czoschke, Augusto Morrone, Dimitar Dimtrov, Song Xue, Yonghua Chen
Current-perpendicular-to the plane (CPP) giant magnetoresistive (GMR) sensors with a current-confined-path (CCP) layer inserted within the Cu spacer have been manufactured using ultrahigh vacuum PVD sputtering, photolithography, and ion milling processes. Compared with a pure metallic CPP system, the CCP insertion layer enables a substantial increase in sensor resistance with an equivalent or better GMR ratio, and thus a significant improvement in the ΔRA amplitude. Heads with such a sensor have been tested under various bias currents, both quasistatically and on a spinstand. It was found that the resistance of the sensors increases with increasing bias current and voltage, following typical metallic behavior. Also, the CCP insertion layer enables operation at higher bias currents compared with the pure metallic sensors (without the insertion layer) and thus a higher output signal. This effect is attributed to less magnetic instability due to the reduced Ampere fields around the narrow (∼6 nm) current-confined paths. Finally, the CPP-GMR heads with CCP layer were tested under high-density recording conditions using the perpendicular recording media. Bit error rate (BER) as a function of linear density is reported. Microtrack profiles were also recorded to determine track density capability.
Keywords: Current-perpendicular-to the plane (CPP); Giant magnetoresistive (GMR); Current-confined-path (CCP); Bit error rate (BER)

Effects of controlling Cu spacer inter-diffusion by diffusion barriers on the magnetic and electrical stability of GMR spin-valve devices Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 322, Issue 13, July 2010, Pages 1834-1840
Jing Jiang, Ding Gui Zeng, Hojun Ryu, Kyung-Won Chung, Seongtae Bae
An ultra-thin Co or CoFe diffusion barrier inserted at the NiFe/Cu interfaces was revealed to effectively control the electrical and magnetic stability of NiFe/Cu/NiFe-based giant magnetoresistance (GMR) spin-valve spintronics devices (SVSDs) operating at high current density. It was found that the activation energy, Ea, related to the electromigration (EM)-induced inter-diffusion process for the patterned NiFe(3)/Cu(2)/NiFe(3 nm) magnetic multi-layered devices (MMLD) was remarkably increased from 0.52±0.2 eV to 1.17±0.16 eV after the insertion of an ultra-thin Co diffusion barrier at the NiFe/Cu interfaces. The dramatically reduced “current shunting paths” from the Cu spacer to the NiFe thin films and the development of “self-healing process” resulted from the effectively restrained Cu inter-diffusion (intermixing with Ni atoms) due to the diffusion barriers were found to be primarily responsible for the improvement of electrical and magnetic stability. The further investigation on the effects of controlling Cu spacer inter-diffusion by diffusion barriers on the EM and thermomigration (TM)-induced magnetic degradation was carried out for the NiFe/(Co or Co90Fe10)/Cu/(Co or Co90Fe10)/NiFe/FeMn top exchange-biased GMR (EBGMR) SVSDs electrically stressed under the applied DC current density of J=2.5×107 A/cm2 (I=16.5∼17.25 mA). It was clearly confirmed that the Co and the CoFe diffusion barriers effectively control the Cu spacer inter-diffusion resulting in a smaller reduction in both GMR ratio and exchange bias field of the EBGMR SVSDs. Furthermore, it was obviously observed that the effects of CoFe diffusion barrier on controlling the Cu spacer inter-diffusion are more significant than that of Co. The effectively reduced Mn atomic inter-diffusion at the NiFe/FeMn interface and the well-maintained interfacial spin-dependent scattering resulted from the control of EM and TM-induced Cu spacer inter-diffusion were the main physical reasons for the significant improvement of magnetic and electrical degradation of top EBGMR SVSDs.
Keywords: Controlling of Cu spacer inter-diffusion; Electrical and magnetic stability; GMR Spin-valve device; Co and CoFe diffusion barrier

Temperature dependence of GMR and effect of annealing on electrodeposited Co–Ag granular films Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 322, Issue 20, October 2010, Pages 3186-3191
Jose Garcia-Torres, Elisa Vallés, Elvira Gómez
The magnetoresistance of Co–Ag granular films composed of superparamagnetic and ferromagnetic particles was studied at different temperatures. The increase in the GMR values while decreasing temperature down to 20 K was quantified. The non-saturating behaviour of the MR(H) curves was retained even at the lowest measurement temperature, which was mainly attributed to the dipolar interaction among the superparamagnetic particles. The influence of the annealing conditions on the magnetoresistance was also studied. In all conditions, a decrease in the GMR values was measured being attributed to an increase in the particle size.
Keywords: Co–Ag; Granular film; GMR; Temperature dependence; Annealing

GMR sensors: Magnetoresistive behaviour optimization for biological detection by means of superparamagnetic nanoparticles
Biosensors and Bioelectronics, Volume 26, Issue 8, 15 April 2011, Pages 3705-3709
A. Manteca, M. Mujika, S. Arana
An immunomagnetic method for the selective and quantitative detection of biological species by means of a magnetoresistive biosensor and superparamagnetic particles has been optimized. In order to achieve this, a giant magnetoresistive [Co (5.10 nm)/Cu (2.47 nm)]20 multilayer structure has been chosen as the sensitive material, showing a magnetoresistance of 3.60% at 215 Oe and a sensitivity up to 0.19 Ω/Oe between 145 Oe and 350 Oe. The outward gold surface of the sensor is biofunctionalized with a Self-Assembled Monolayer (SAM).
In addition, three different types of magnetic labels have been tested. 2 μm diameter magnetic carriers (7.68 pg ferrite/particle) have shown the best response and they have induced a shift in the magnetoresistive hysteresis loops up to 9% at 175 Oe.
Keywords: BioMEMS; GMR; Magnetic particles; SAM

GMR biosensor arrays: Correction techniques for reproducibility and enhanced sensitivity
Biosensors and Bioelectronics, Volume 25, Issue 9, 15 May 2010, Pages 2177-2181
D.A. Hall, R.S. Gaster, S.J. Osterfeld, B. Murmann, S.X. Wang
Giant magnetoresistive biosensors possess great potential in biomedical applications for quantitatively detecting magnetically tagged biomolecules. Magnetic sensing does not suffer from the high background levels found in optical sensing modalities such as the enzyme linked immunosorbent assay translating into a technology with higher sensitivity. However, to reveal the full potential of these sensors and compensate for non-idealities such as temperature dependence, digital correction and calibration techniques are not only useful but imperative. Using these calibration techniques to correct for process variations and dynamic changes in the sensing environment (such as temperature and magnetic field), we are able to obtain extremely sensitive and, more importantly, reproducible results for quantifiable biomolecular reorganization. The reproducibility of the system was improved by over 3× using digital correction techniques and the sensors are made temperature independent by using a novel background correction technique.
Keywords: GMR correction algorithms; Temperature correction; Biosensors; Adaptive filter

GMR biosensor arrays: A system perspective Original Research Article
Biosensors and Bioelectronics, Volume 25, Issue 9, 15 May 2010, Pages 2051-2057
D.A. Hall, R.S. Gaster, T. Lin, S.J. Osterfeld, S. Han, B. Murmann, S.X. Wang
Giant magnetoresistive biosensors are becoming more prevalent for sensitive, quantifiable biomolecular detection. However, in order for magnetic biosensing to become competitive with current optical protein microarray technology, there is a need to increase the number of sensors while maintaining the high sensitivity and fast readout time characteristic of smaller arrays (1–8 sensors). In this paper, we present a circuit architecture scalable for larger sensor arrays (64 individually addressable sensors) while maintaining a high readout rate (scanning the entire array in less than 4 s). The system utilizes both time domain multiplexing and frequency domain multiplexing in order to achieve this scan rate. For the implementation, we propose a new circuit architecture that does not use a classical Wheatstone bridge to measure the small change in resistance of the sensor. Instead, an architecture designed around a transimpedance amplifier is employed. A detailed analysis of this architecture including the noise, distortion, and potential sources of errors is presented, followed by a global optimization strategy for the entire system comprising the magnetic tags, sensors, and interface electronics. To demonstrate the sensitivity, quantifiable detection of two blindly spiked samples of unknown concentrations has been performed at concentrations below the limit of detection for the enzyme-linked immunosorbent assay. Lastly, the multiplexing capability and reproducibility of the system was demonstrated by simultaneously monitoring sensors functionalized with three unique proteins at different concentrations in real-time.
Keywords: Magnetic biosensor; GMR biosensor; Spin-valve biosensor; Multiplexing spin-valves

Electrodeposited multilayer films with giant magnetoresistance (GMR): Progress and problems Review Article
Progress in Materials Science, Volume 55, Issue 3, March 2010, Pages 107-245
I. Bakonyi, L. Péter
The giant magnetoresistance (GMR) effect was discovered in 1988 in nanoscale metallic ferromagnetic/non-magnetic (FM/NM) multilayers. By now, devices based on this phenomenon have been widely commercialized which use multilayered structures manufactured via physical deposition (PD) methods, mainly sputtering. It was shown in the early 1990s that electrodeposition (ED) is also capable of producing multilayered magnetic nanostructures exhibiting a significant GMR effect. These layered structures include multilayer films similar to those prepared by PD methods on macroscopic substrates and multilayered nanowires deposited into nanosized template pores, the latter ones being unique to the ED technique. Whereas ED multilayered nanowires can exhibit a GMR effect comparable to the values obtained on PD multilayer films, the GMR values achieved on ED multilayer films still remain inferior to them and, quite often, require high magnetic fields for saturation. Therefore, in spite of the relative simplicity and cost-effectiveness of the ED method, the GMR characteristics of ED multilayer films are still not competitive with the corresponding parameters of their PD counterparts. The main purpose of the present review is to give a summary of the progress achieved over the last one and a half decades on ED multilayer films with GMR effect and to critically evaluate the GMR results reported for various element combinations accessible to the ED technique for the preparation of FM/NM multilayer films (ED multilayered nanowires will be treated very briefly only). In order to promote an understanding of the inferior behavior of ED multilayer films, a detailed discussion of the magnetoresistance effects occurring in bulk homogeneous ferromagnets as well as in magnetic nanostructures (FM/NM multilayers and granular alloys) will be provided. Particular attention will be paid to the case of non-ideal magnetic nanostructures which contain both FM and superparamagnetic (SPM) regions. This is an essential ingredient in explaining the high saturation field of GMR commonly observed in ED multilayer films. In addition to the GMR magnitude, this is another characteristic decisively influencing the magnetic field sensitivity, a key feature concerning applications in sensor devices. The controversial results reported for the spacer layer thickness dependence of GMR in ED multilayer films will also be discussed. It is pointed out that the still inferior GMR characteristics of ED multilayer films can be to a large extent ascribed to microstructural features leading to the appearance of SPM regions, pinholes in the spacer layers and probably not sufficiently perfect interfaces between the FM and NM layers. The origin of the latter deficiency is not yet well understood although it is clearly one of the main causes of a weak interlayer coupling (if there is any coupling at all) and, thus, a small degree of antiparallel alignment leading to a reduced GMR effect. Works will also be described in which attempts were made to produce ED multilayer films with view on possible applications in GMR sensor devices. Finally, problems will be identified which should still be solved in order to make the properties of ED multilayer films attractive for GMR applications.

Detection and characterization of defects using GMR probes and artificial neural networks Original Research Article
Computer Standards & Interfaces, Volume 33, Issue 2, February 2011, Pages 191-200
O. Postolache, H. Geirinhas Ramos, A. Lopes Ribeiro
This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing device. Non-destructive tests in aluminum plates are applied in order to extract information about possible defects: cracks, holes and other mechanical damages. Eddy-current testing (ECT) presents major benefits such as low cost, high checking speed, robustness and high sensitivity to large classes of defects. Coil based architecture probes or coil-magnetoresistive probes are usually used in ECT. In our application the GMR sensor is used to detect a magnetic field component parallel to a plate surface, when an excitation field perpendicular to the plate is imposed. A neural network processing architecture, including a multilayer perceptron and a competitive neural network, is used to classify defects using the output amplitude of the eddy-current probe (ECP) and its operation frequency. The crack detection, classification and estimation of the geometrical characteristics, for different classes of defects, are described in the paper.
Keywords: Non-destructive testing; Eddy currents; Magnetoresistive sensor; Neural network classifier

New numerical modelling of the mechanical long-term behaviour of the GMR gallery in ANDRA’s Underground Research Laboratory Original Research Article
Physics and Chemistry of the Earth, Parts A/B/C, In Press, Corrected Proof, Available online 3 August 2011
Laura Blanco Martín, Faouzi Hadj-Hassen, Michel Tijani, Gilles Armand
This paper deals with a new macroscopic numerical modelling of the mechanical long-term behaviour of ANDRA’s Underground Research Laboratory. The study focuses on the GMR gallery, oriented along the minor horizontal principal stress and located at the main level 490 m deep. The simulations are made using the finite element method (FEM).
Convergence measurements in this gallery exhibit an important dissymmetry between the vertical and horizontal directions, as well as a significant time effect in the vertical trend. In attempts to both understand the phenomena that lie beneath such dissymmetry and reproduce the experimental data, a modification to Lemaître’s creep law has been proposed. The new viscoplastic law takes into account the following aspects: rock transverse isotropy, creep behaviour and rock expansion. The excavation history of the GMR gallery has also been considered in the numerical modelling.
The numerical results are very satisfactory for the GMR drift. However, the mechanisms of anisotropic shear and expansion on which the new law is based do not lead to an accurate reproduction of the data measured in the galleries oriented in the perpendicular direction. Therefore, a thorough insight into the mechanical behaviour of the rock mass and into the proposed new law is needed before the latter can be applied to the Callovo-Oxfordian layer.

Electrodeposition and characterization of Cu/Co multilayers: Effect of individual Co and Cu layers on GMR magnitude and behavior Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 8, April 2009, Pages 974-978
D.K. Pandya, Priyanka Gupta, Subhash C. Kashyap, S. Chaudhary
The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12–14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.
Keywords: Magnetic multilayer; Magnetoresistance; Electrodeposition

Unconventional GMR angular dependence using a compensated ferrimagnet Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 322, Issues 9-12, May-June 2010, Pages 1428-1430
N.T. Nam, L. Ranno
We have designed a GdCo/Cu/NiFe giant magnetoresistance (GMR) trilayer, the magnetoresistance of which does not always depend on the angle between the magnetisations of the electrodes. Using a GdCo ferrimagnetic alloy close to compensation, it was possible to experimentally reach the spin flop field Bsf of the ferrimagnetic layer. Below Bsf, the ferrimagnetic layer behaves as a ferromagnetic layer, however above Bsf, the ferrimagnetic sublattice magnetisations are no longer antiparallel and rotate 90∘ away from the GdCo layer total magnetisation, i.e. 90∘ away from the applied field. The GMR responds to the angle between Co and NiFe magnetisations and not to the angle between GdCo and NiFe magnetisations. Such a structure allows to study the change of sign of the GdCo spin polarisation as a function of temperature, and details of the GdCo magnetisation when usual magnetometry is difficult. FeNi can be seen as a sensor for the in-plane component of Co sublattice magnetisation, whereas extraordinary Hall effect measurements give a complementary image of the perpendicular component of the Co magnetisation.
Keywords: Ferrimagnetism; Giant magnetoresistance; Compensation temperature

Development of new positive-selection RIVET tools: Detection of induced promoters by the excision-based transcriptional activation of an aacCI (GmR)–gfp fusion Original Research Article
Journal of Biotechnology, Volume 155, Issue 2, 10 September 2011, Pages 147-155
M.J. Lozano, M.E. Salas, M.A. Giusti, W.O. Draghi, G.A. Torres Tejerizo, M.C. Martini, M.F. Del Papa, M. Pistorio, A. Lagares
RIVET (Recombination Based in vivo Expression Technology) is a powerful genetic tool originally conceived for the identification of genes induced in complex biological niches where conventional transcriptomics is difficult to use. With a broader application, genetic recombination-based technologies have also been used, in combination with regulatory proteins and specific transcriptional regulators, for the development of highly sensitive biosensor systems. RIVET systems generally comprise two modules: a promoter-trap cassette generating genomic transcriptional fusions to the tnpR gene encoding the Tn-γδ TnpR resolvase, and a reporter cassette carrying res-flanked selection markers that are excised upon expression of tnpR to produce an irreversible, inheritable phenotypic change.
We report here the construction and validation of a new set of positive-selection RIVET systems that, upon induction of the promoter-trap module, generate the transcriptional activation of an antibiotic-resistant and a green-fluorescent phenotype. Two classes of promoter-trap tools were constructed to generate transcriptional fusions to tnpR: one based on the use of a narrow-host-range plasmid (pRIVET-I), integrative in several Gram-negative bacteria, and the other based on the use of a broad-host-range plasmid (pRIVET-R). The system was evaluated in the model soil bacterium Sinorhizobium meliloti, where a clear-cut phenotypic transition from NmR-GmS-GFP− to NmS-GmR-GFP+ occurred upon expression of tnpR. A S. meliloti integrative RIVET library was constructed in pRIVET-I and, as expected, changes in the extracellular conditions (e.g., salt stress) triggered a significant increase in the appearance of GmR-GFP+ (excised) clones. The sacB-independent positive-selection RIVET systems here described provide suitable basic tools both for the construction of new recombination-based biosensors and for the search of bacterial markers induced when microorganisms colonize and invade complex environments and eukaryotic hosts.
Keywords: RIVET; IVET; Positive-selection; Bacteria–host interaction; Sinorhizobium meliloti; Biosensor

Formation of a nanobarrel structure in CPP-GMR spin-valve films Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 322, Issues 9-12, May-June 2010, Pages 1449-1451
Yoshihiko Fuji, Hiromi Yuasa, Hideaki Fukuzawa
As a new approach for current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) spin-valve films, we have proposed a new nanostructure to cause mesoscopic phenomena. For this purpose, we have successfully formed a nanobarrel structure composed of Cu granular-like shape surrounded by Al2O3 insulator in which Cu nanoconducting channel punches through the Al2O3 insulator both at the top and at the bottom. This nanobarrel structure was confirmed by high-resolution transmission electron microscope (HR-TEM) analysis. Both the resistance–voltage characteristics and the resistance–temperature characteristics showed the metallic conductance property, which is in good agreement with the nanostructure identified by HR-TEM analysis. The nanobarrel structure offers features compatible with both nano-ordered electron-confined structure by insulator and low resistance with metallic conductance.
Keywords: Current-perpendicular-to-plane giant magneto-resistance; Spin-valve; Nanobarrel; Nano-oxide layer; Current-confined-path

Microstructure formation in electrodeposited Co–Cu/Cu multilayers with GMR effect: Influence of current density during magnetic layer deposition Original Research Article
Acta Materialia, Volume 59, Issue 8, May 2011, Pages 2992-3001
D. Rafaja, C. Schimpf, T. Schucknecht, V. Klemm, L. Péter, I. Bakonyi
The influence of the current density applied during deposition of magnetic layers on the microstructure formation in electrodeposited Co–Cu/Cu multilayers and on their giant magnetoresistance was investigated using a combination of magnetoresistance measurements, wide-angle and small-angle X-ray scattering, high-resolution transmission electron microscopy, atomic force microscopy and X-ray spectroscopy. The magnetoresistance measurements revealed that a reduction in the current density stimulates a transition from the formation of the magnetic layers with predominantly ferromagnetic character to the formation of superparamagnetic regions. As based on electrochemical considerations, it was supposed that such a change in the magnetic properties can be caused by an increased amount of Cu codeposited with Co at low current densities. It turned out from the structural studies that a pronounced segregation of Co and Cu occurs at low current densities. In accordance with their very low mutual solubility at room temperature, no atomic scale intermixing of Co and Cu could be detected. The segregation of Cu and Co was related to the fragmentation of the magnetic layers, to the enhancement of the local lattice strains, to the increase in the interface corrugations, to the partial loss of the multilayer periodicity and, finally, to the formation of Co precipitates in the Cu matrix.
Keywords: Electrochemistry; Multilayers; Giant magnetoresistance; X-ray scattering; Transmission electron microscopy

Tunneling vs. giant magnetoresistance in organic spin valve Original Research Article
Synthetic Metals, Volume 160, Issues 3-4, February 2010, Pages 216-222
Jung-Woo Yoo, H.W. Jang, V.N. Prigodin, C. Kao, C.B. Eom, A.J. Epstein
We studied magnetoresistance (MR) in La2/3Sr1/3MnO3 (LSMO)/organic semiconductor (OSC)/Fe heterojunction devices using rubrene (C42H28) as an organic semiconductor. Efficient spin polarized tunneling using a hybrid barrier (oxide (1.2 nm)/rubrene (5 nm)) was observed. Devices with a thin layer of rubrene as the barrier may have magnetic clusters and/or pinholes in the barrier, which could explain significant variations of MR among devices. As the thickness of the rubrene layer is increased, device current becomes strongly limited by carrier injection resulting in strong temperature and bias dependent device resistance. The carrier injection in these devices can be described with thermionic field emission at the metal/OSC interface and is analyzed with both empirical and theoretical models. The effect of carrier transport through the spacer on the magnetoresistance for organic-based spin valve is discussed. The observed giant magnetoresistance (GMR) in 20 nm rubrene device demonstrates the spin polarized carrier injection and transport through the rubrene OSC layer.
Keywords: Organic spin valve; Tunneling magnetoresistance; Giant magnetoresistance; Spin injection; Thermionic field emission

Preparation and giant magnetoresistance of electrodeposited Co–Ag/Ag multilayers Original Research Article
Thin Solid Films, Volume 517, Issue 21, 1 September 2009, Pages 6081-6090
J. García-Torres, L. Péter, Á. Révész, L. Pogány, I. Bakonyi
Electrodeposition of Co–Ag/Ag multilayers along with their giant magnetoresistance (GMR) was investigated. The electrodeposition process was optimized for both minimizing the dissolution of the Co layer and achieving a high magnetoresistance. Structural analysis of Co–Ag/Ag deposits revealed that silver has an fcc structure, whereas cobalt crystallizes in the hcp structure. No solid solution of Co and Ag was detected. The X-ray diffraction study did not show any satellite reflection. A GMR of the order of 0.5% and 2% could be observed at room temperature and at 20 K, respectively, with both superparamagnetic and ferromagnetic GMR contributions throughout the temperature range studied.
Keywords: Multilayer; Cobalt; Silver; Electrodeposition; Giant magnetoresistance (GMR)

Giant Magnetoresistance and Coercivity of electrodeposited multilayered FeCoNi/Cu and CrFeCoNi/Cu Original Research Article
Journal of Magnetism and Magnetic Materials, In Press, Corrected Proof, Available
online 26 August 2011
P. Shakya, B. Cox, D. Davis
The effect of Cr addition on electrodeposited multilayered nanowires CrFeCoNi/Cu was investigated from a magnetic property perspective: current perpendicular to the plane-Giant Magnetoresistance (CPP-GMR) and Coercivity (BH loops). The magnetic behavior of multilayered nanowires of CrFeNiCo/Cu was also affected by the alloy deposition potential, alloy pulsing time (layer thickness) and number of bilayers. Furthermore, the addition of Cr influenced both the nanowires GMR and Coercivity. Cr addition to the ferromagnetic FeCoNi layer induced a reduction in the room temperature GMR from 10.64% to 5.62%; however, the magnetic saturation field decreased from 0.45 to 0.27 T. The increase in the number of bilayers, from 1000 to 2500, resulted in a higher GMR value, 14.56% with 0.35 T magnetic saturation field. Addition of Cr to the ferromagnetic layer decreased the coercivity from 0.015 to 0.0054 T. Low saturation field CPP-GMR nanowires showing low coercivity at room temperature opens a new door for magnetic sensing devices. To the best of our knowledge, this is the first study on electrodeposited CrFeCoNi/Cu multilayered nanowires.
Keywords: Giant magnetoresistance; GMR; Coercivity; Electrodeposition; Multilayer; Nanowire; CrFeCoNi/Cu; Read head

Giant magnetoresistance in a two-dimensional electron gas modulated by periodically repeated magnetic barriers
Solid State Communications, Volume 150, Issues 41-42, November 2010, Pages 2023-2027
G. Papp, S. Borza
The giant magnetoresistance effect is investigated in a two-dimensional electron gas modulated by periodically repeated magnetic barriers, which can be realized by depositing parallel ferromagnets on the top and the bottom of a heterostructure. It is found that the magnetoresistance ratio (MRR) of the present system shows a strong dependence on the number of ferromagnetic unit cells. The modified MRR (MMRR) shows oscillations, where the number of peaks is determined by the number of units, and our study indicates that for experimentally accessible parameters for a GaAs heterostructure the value of the MMRR can be as high as 55% for a realistic electron density.
Keywords: A. Two-dimensional electron gas; A. Ferromagnetic strips; D. Giant magnetoresistance

Modelling the sensitivity of infrared emissivity of magnetic thin films to giant magnetoresistance Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 5, March 2009, Pages 354-360
S.M. Stirk, S.M. Thompson, J.A.D. Matthew
The correlation between emissivity and giant magnetoresistance (GMR) in magnetic thin films is investigated at infrared (IR) wavelengths using a thin-film model of emissivity. The sensitivity of emissivity to GMR is shown to depend upon film thickness, and agrees excellently with bulk-material results for films thicker than the material skin depth. However, for films thinner than the skin depth the sensitivity to GMR is shown to weaken. In addition, at mid-to-far IR wavelengths the spectral dependence of the correlation is investigated using a modified Drude-type expression for the refractive index combined with the thin-film model. This is applied to a multilayered GMR material, and the sensitivity of emissivity to GMR is shown to have a similar spectral dependence to that of the magnetorefractive effect. An analytical interpretation in terms of skin depth is also developed at long wavelengths, and shown to agree excellently with thin-film simulations.
Keywords: Emissivity; Infrared; Giant magnetoresistance; Remote sensing; Magnetorefractive effect

Behavior of giant magnetoresistance in Co–Cu–Co pseudo spin-valves after magnetic annealing Original Research Article
Thin Solid Films, In Press, Corrected Proof, Available online 24 August 2011
M. Jergel, Y. Halahovets, P. Šiffalovič, K. Végsö, R. Senderák, E. Majková, Š. Luby
The Co/Cu/Co pseudo spin-valves were e-beam evaporated onto silicon substrates covered with thermal oxide. The X-ray diffraction and X-ray reflectivity showed polycrystalline layer structure and conformal interface roughness, respectively, giving rise to the Néel coupling. The longitudinal magneto-optical Kerr effect measurements revealed a deposition induced in-plane magnetic anisotropy in the thicker (magnetically hard) Co layer. The maximum giant magnetoresistance (GMR) ratio for magnetization along the hard axis was found to be by 30% higher than that for magnetization along the easy axis. A series of successive 1 hour thermal annealings from 100 °C to 350 °C in a saturation magnetic field applied along the easy axis lead gradually up to a 20% relative enhancement and reduction of GMR for magnetization along the hard and easy axes, respectively. This annealing behavior may be explained by a faster magnetic anisotropy growth in the thicker Co layer than in the thinner one due to the deposition induced anisotropy and better developed starting polycrystalline structure as expected for larger thickness. An annealing induced 0.8 kA/m reduction of the Néel coupling derived from modified interface parameters and annealing out of defects play a secondary role in GMR modification.
Keywords: Spin valve; Giant magnetoresistance; Néel coupling; X-ray reflectivity; Grazing-incidence small-angle X-ray scattering; Magneto-optical Kerr effect

Giant magnetoresistance of Co/ITO multilayers
Solid State Communications, Volume 149, Issues 47-48, December 2009, Pages 2254-2256
Ling Lü, Gang Lü, Zhaogang Zhang, Chunhong Gao, Tian Yu, Peng Chen
The electrical and magnetic properties of Co/ITO multilayers with various ITO layer thickness are studied. Negative giant magnetoresistance with a maximum of −1.9% at room temperature and −2.57% at 15 K are observed. The magnitudes of GMR oscillate with a period of about 1 nm when varying the thickness of ITO layer.
Keywords: A. Ferromagnetic metal–semiconductor; A. Indium tin oxide; A. Multilayers; D. Giant magnetoresistance

Giant room-temperature magnetoresistance in La0.8Tb0.2MnO3 under the low magnetic fields Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 9, May 2009, Pages 1199-1201
Ying-Tang Zhang, Zi-Yu Chen, Chun-Chang Wang, Qiu Jie, Hui-Bin Lü
Polycrystalline perovskite La0.8Tb0.2MnO3 (LTMO) with an orthorhombic phase was synthesized by conventional solid-state reaction. The magnetic and electric properties of La0.8Tb0.2MnO3 were examined. The striking finding is that the material exhibits giant magnetoresistance at room temperature as high as −31.8% and −35.7% under the low magnetic fields of 100 and 1000 Oe, respectively. This result suggests that La0.8Tb0.2MnO3 has a promising potential in future device developments.
Keywords: Perovskite; La0.8Tb0.2MnO3; X-ray diffraction (XRD); Giant magnetoresistance (GMR)

Magnetic/structural phase diagram and enhanced giant magnetoresistance in Zn-doped antiperovskite compound Ga1−xZnxCMn3 Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 323, Issue 17, September 2011, Pages 2233-2237
C.C. Li, B.S. Wang, S. Lin, J.C. Lin, P. Tong, W.J. Lu, Y.P. Sun
The structural, magnetic and electrical transport properties of Zn-doped antiperovskite compounds Ga1−xZnxCMn3 (0≤x≤0.30) have been investigated. After partial substitution of Zn for Ga, the Curie temperature increases monotonously and the ground antiferromagnetic (AFM)-ferromagnetic intermediate (FI) phase transition is gradually suppressed. With increasing the doping level x, the saturated magnetizations decreases gradually firstly for x≤0.20, then increases with increasing x. The electrical transport properties of Ga1−xZnxCMn3 are studied at different magnetic fields. Enhanced giant magnetoresistance (GMR) was observed around the AFM-FI transition. With increasing x, the maximal values and peak widths of GMR increase. Particularly, for x=0.20, GMR reaches a maximum value of 75%, spanning a temperature range of 80 K at 50 kOe and displays the behavior of strongly depending on the magnetization history. The possible origins are discussed.
Keywords: Antiperovskite; Magnetic properties; Giant magnetoresistance; GaCMn3

Effect of nano-oxide layers on giant magnetoresistance in pseudo-spin-valves using Co2FeAl electrodes Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 323, Issue 5, March 2011, Pages 631-634
D.L. Zhang, X.G. Xu, Y. Wu, J. Miao, Y. Jiang
We studied the pseudo-spin-valves (PSVs) with a structure of Ta/Co2FeAl/NOL1/Co2FeAl/Cu/Co2FeAl/NOL2/Ta, where NOL represents the nano-oxide layer. Compared with the normal Co2FeAl (CFA) PSV with a structure of Ta/Co2FeAl/Cu/Co2FeAl/Ta, which shows only a current-in-plane (CIP) giant magnetoresistance (GMR) of 0.03%, the CFA PSV with NOLs shows a large CIP-GMR of 5.84%. The enhanced GMR by the NOLs inserted in the CFA PSV is due to the large specular reflection caused by [(CoO)(Fe2O3)(Al2O3)] in NOL1 and [(Fe2O3)(Al2O3)(Ta2O5)] in NOL2. Another reason is that the roughness of the interface between Ta and CFA is improved by the oxidation procedure.
Keywords: Nano-oxide layers; Heusler alloy; Giant magnetoresistance

Giant magnetoresistance of Fe/In/Fe trilayers Original Research Article
Journal of Alloys and Compounds, Volume 486, Issues 1-2, 3 November 2009, Pages 18-21
Liangmin Wang, Ke Chen, Zhaogang Zhang, Shenfen Hao, Peng Chen
Giant magnetoresistance (GMR) and magnetic properties in Fe/In/Fe trilayers with various In thickness were studied. Negative GMR 0.38% was observed in sample with In thickness 1.05 nm at 20 K. The magnitudes of GMR were found to oscillate with a period about 1.1 nm when varying the thickness of In layers. The GMR of trilayers was near constant at low temperature and decreased linearly with increasing temperature at high temperature.
Keywords: Magnetic films and multilayers; Nanofabrications; Magnetic measurements; Giant magnetoresistance; Antiferromagnetically coupled

Giant magnetoresistance in electrodeposited Co–Ag granular films
Materials Letters, Volume 65, Issue 12, 30 June 2011, Pages 1865-1867
Jose Garcia-Torres, Elisa Vallés, Elvira Gómez
We report on the electrodeposition of Co–Ag granular films with GMR from a chloride-based electrolyte. Two different electrochemical techniques (chronoamperometry and pulse plating) were used to prepare the films. Both electrochemical and TEM analysis have revealed the heterogeneity of the as-deposited samples. GMR values up to 7% at room temperature were measured. The longitudinal (LMR) and transverse (TMR) magnetoresistance were practically indistinguishable indicative of real granular systems. An appropriate numerical analysis of the magnetoresistance curves showed high superparamagnetic contribution to the total MR.
Keywords: Electrodeposition; Giant magnetoresistance; Cobalt–silver; Granular system

Co-existence of giant magnetoresistance and large magnetocaloric effect near room temperature in nanocrystalline La0.7Te0.3MnO3 Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 322, Issue 17, September 2010, Pages 2537-2540
Rabindra Nath Mahato, K. Sethupathi, V. Sankaranarayanan, R. Nirmala
Sol–gel prepared nanocrystalline La0.7Te0.3MnO3 has rhombohedral crystal structure (space group R3¯C) at room temperature and orders ferromagnetically at ∼280 K (TC). A large magnetic entropy change of ∼12.5 J kg−1 K−1 is obtained near TC for a field change of 50 kOe. This magnetocaloric effect could be explained in terms of Landau theory. The temperature dependence of electrical resistivity shows metal–insulator transition at TC and a giant magnetoresistance of ∼52% in 50 kOe. The co-existence of giant magnetoresistance and large magnetocaloric effect near room temperature makes nanocrystalline La0.7Te0.3MnO3 a promising material for magnetic refrigeration and spintronic device applications.
Keywords: Oxide; Magnetoresistance; Magnetocaloric effect

Giant magnetoresistance due to electron-hole pair mechanism in poly(N-vinylcarbazole) Original Research Article
Synthetic Metals, Volume 160, Issues 3-4, February 2010, Pages 285-290
Tadaaki Ikoma, Toshinari Ogiwara, Yutaka Takahashi, Kimio Akiyama, Shozo Tero-Kubota, Yuka Takahashi, Tomohiro Suzuki, Yusuke Wakikawa
An amorphous molecular semiconductor, poly(N-vinylcarbazole) (PVCz), exhibits negative giant magnetoresistance (MR) under ambient conditions. The application of a weak magnetic field of 10 mT to PVCz films doped with lumichrome, in which light excitation immediately creates triplet electron-hole (e-h) pairs that are precursors of photocarriers, causes a steep decrease in resistivity by more than 20% at ambient temperature. Further, the resistivity of the doped film gradually reduces by approximately one-half under a field of 1 T, equivalent to an MR ratio of −55%. In addition, anomalous spikes are also detected at 0.07, 0.30, and 9.0 T, indicative of an exponential dependence with a decay distance of 0.1 nm in the exchange interaction of the e-h pair. A quantum mechanical calculation based on the density operator formalism clarifies that the observed MR effect can be comprehensively understood by the spin-selective charge dynamics and the coherent and incoherent spin dynamics of the e-h pair in a quasi-one-dimensional lattice for photocarrier generation. Model calculations also indicate the importance of the spin-lattice relaxation for the giant MR effect in organic molecular semiconductors.
Keywords: Magnetoresistance; Electron-hole pair; Spin-selective recombination; Spin relaxation; Photoconduction

Sign-changeable spin-filter efficiency and giant magnetoresistance in seamless graphene nanoribbon junctions Original Research Article
Computational Materials Science, Volume 50, Issue 10, August-September 2011, Pages 2886-2890
Chengyong Xu, Linze Li, Hong Li, Rui Qin, Jiaxin Zheng, Guangfu Luo, Qihang Liu, Xin Yan, Lili Yu, Jing Lu, Zhengxiang Gao
Sign-changeable spin-filter efficiency is predicted in both the ferromagnetic and antiferromagnetic configurations of a zigzag graphene nanoribbon bridging two half-planar graphene electrodes from ab initio quantum transport calculations. By changing edge spin-polarization configuration, we obtain giant room-temperature magnetoresistance, which is one order of magnitude larger than the maximum experimental results.
Keywords: Graphene nanoribbon; Spin-filter efficiency; Magnetoresistance; Quantum transport calculation

Effects of bulk and interface scattering on giant magnetoresistance in the Co/Cu multilayer systems
Computational Materials Science, Volume 50, Issue 2, December 2010, Pages 800-804
B. Elsafi, F. Trigui, Z. Fakhfakh
The evolution of the giant magnetoresistance (GMR) effect in thin film multilayers based on (Co/Cu)n has been investigated by using semi-classical approach of the two spin channel currents developed by Hood, Falicov and Penn. The in plane MR of Co/Cu multilayers is calculated for correlated quasiperiodic interfaces. The numerical results show important influence of interface roughness on the behaviour of MR. The variation of MR with phenomenological parameters S↑ and S↓ for two directions of spin and relaxation time is reported. This interface roughness has been successfully included in our GMR simulation using a semi-classical description to analyse the experimental results giving the variation of MR with the thickness of the copper interlayer.
Keywords: Magnetoresistance; Multilayers; Interface; Roughness

Superparamagnetism and giant magnetoresistance in sputtered FeCuAg granular films Original Research Article
Physica B: Condensed Matter, Volume 405, Issue 1, 1 January 2010, Pages 345-351
S. Rout, M. Senthil Kumar, D.K. Aswal, S.K. Gupta
Magnetization and magnetoresistance studies were carried out on the granular FexCuyAgz films prepared by dc magnetron sputtering. In this series of samples, we have substituted Ag in the parent Fe–Cu system such that the Ag concentration increases from zero while that of the Cu decreases to zero when we go from one sample to another. The blocking temperatures of the films lie in the range 20–50 K. By using a model, the room temperature magnetization data have been analyzed by determining the contributions from the smaller superparamagnetic particles and larger ferromagnetic particles. Size distributions of the superparamagnetic particles are obtained. The magnetoresistance and (M/Ms)2 data do not agree for most of the samples investigated. This discrepancy is due to the fact that the (M/Ms)2 behavior is valid for purely superparamagnetic particles of only one size whereas there are both superparamagnetic and ferromagnetic particles in our samples. When we analyzed the magnetoresistance data using a superparamagnetic model, a good agreement between the experimental data and the simulated data were obtained for some samples. Significant discrepancy observed for other samples may be due to the spin dependent scattering of the electrons traveling from superparamagnetic to ferromagnetic particles or vice versa.
Keywords: Magnetoresistance; Magnetic thin film; Hysteresis; Superparamagnetism; Particle size distribution

Magnetorelaxometry using Improved Giant MagnetoResistance Magnetometer Original Research Article
Sensors and Actuators A: Physical, Volume 159, Issue 2, May 2010, Pages 184-188
M. Denoual, S. Saez, F. Kauffman, C. Dolabdjian
Magnetorelaxometry measurements on immobilized superparamagnetic magnetite (Fe3O4) nanoparticles in freeze-dried samples using a low-cost Improved Giant MagnetoResistance Magnetometer (IGMRM) are presented. Fits to relaxation phenomenological model based on Moment Superposition Model (MSM) are used to extract the characteristic values. Concentrations of iron down to 3.85 μmol are identified in a 150 μl volume from experimental measurements. Also, the extracted amplitude characteristic value confidence intervals associated to measurements and detection performances are given.

Effect of interface number on giant magnetoresistance Original Research Article
Journal of Physics and Chemistry of Solids, Volume 71, Issue 3, March 2010, Pages 309-313
S.M.S.I. Dulal, E.A. Charles
Ni(Cu)/Cu, Co(Cu)/Cu, and Ni–Co(Cu)/Cu multilayers with a varied number of interfaces (i.e. bi-layers) were electrodeposited on gold coated quartz discs in a flow channel cell by a potentiostatic dual-pulse plating method. It was found that the giant magnetoresistance of these multilayers increased almost linearly with increase in the number of interfaces. This result confirms that the interfaces play a dominating role in giant magnetoresistance. Comparable samples of these three types of multilayers were prepared under identical electrochemical conditions from appropriate baths. The result showed that Ni–Co(Cu)/Cu multilayers exhibited much higher giant magnetoresistance than Ni(Cu)/Cu, and Co(Cu)/Cu multilayers, which was possibly due to the structural differences between the multilayers.
Keywords: A. Multilayers; D. Magnetic properties; D. Superlattices

Giant magnetoresistance in melt spun Cu85Co10Ni5 Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 321, Issue 3, February 2009, Pages 131-136
Stefano Curiotto, Erik Johnson, Federica Celegato, Marco Coisson, Nini Pryds
CuCoNi rapidly solidified alloys are interesting because they display giant magnetoresistance (GMR). In the present work a Cu85Co10Ni5 alloy has been synthesized by melt spinning and analysed for GMR. The ribbons obtained have been annealed at different temperatures and the evolution of the crystal structure with annealing has been studied by X-ray diffraction. The fine microstructure has been observed by TEM and related to the magnetic properties, investigated in a vibrating sample magnetometer. In the studied composition the magnetoresistance was found to be lower than in binary CuCo alloys without Ni addition.
Keywords: Cu alloy; Rapid solidification; GMR; Magnetic property

Giant magnetoresistance effect in a magnetic barrier nanostructure Original Research Article
Superlattices and Microstructures, Volume 49, Issue 2, February 2011, Pages 144-150
Jian-Duo Lu
The giant magnetoresistance (MR) effect is theoretically studied in a magnetically modulated two-dimensional electron gas. We find that the significant transmission difference for electron tunneling through parallel and antiparallel magnetization configurations results in a considerable MR effect. We also find that the MR ratio strongly depends on the magnetic strength and the distance between the left edges of two ferromagnetic strips as well as the temperature.
Keywords: Magnetic nanostructure; MR effect; MR ratio

Giant magnetoimpedance and colossal ac magnetoresistance of a Cu coil wound on La0.67Sr0.33MnO3
Solid State Communications, Volume 151, Issue 1, January 2011, Pages 47-50
Jifan Hu, Yifei Wang, Juan Chen, Hongwei Qin, Bo Li
We observed the giant magnetoimpedance and colossal ac magnetoresistance for a Cu coil wound on La0.67Sr0.33MnO3 under low dc magnetic fields. Even though the dc magnetoresistance for La0.67Sr0.33MnO3 plate is only −2.4% under H=12 kOe, a Cu coil wound on La0.67Sr0.33MnO3 plate exhibits a colossal ac magnetoresistance of −93% at 10 MHz and a giant magnetoimpedance of −59% in a wide frequency range of 500 kHz–10 MHz under a longitudinal field . The transverse magnetoimpedance is weaker than the longitudinal one. The giant magnetoimpedance and colossal ac magnetoresistance for a Cu coil wound on La0.67Sr0.33MnO3 are connected with the variation of permeability induced by dc magnetic field.
Keywords: A. Magnetically ordered materials; D. Electronic transport

Co-contributions of the magnetostriction and magnetoresistance to the giant room temperature magnetodielectric response in multiferroic composite thin films
Solid State Communications, Volume 151, Issues 14-15, July-August 2011, Pages 982-984
Shuai Zhang, Xianlin Dong, Ying Chen, Genshui Wang, Junyu Zhu, Xiaodong Tang
The magnetodielectric properties of BSPT/LSMO multiferroic composite thin films were investigated through the measurement of the frequency dependence of the dielectric constant under different magnetic fields at room temperature. The magnetodielectric (MD) response showed strong frequency dependence: at 100 Hz, the MD response remained negative and the maximum value of −1.1% was obtained; at 52 kHz, the dielectric constant first decreased and then rose linearly with the magnetic field until the giant room temperature positive MD effect of 9.5% was derived under 7 T. The observed unique MD effects for BSPT/LSMO were attributed to the co-contributions of the magnetostriction and magnetoresistance.
Keywords: A. Thin films; D. Dielectric response

X-ray absorption spectroscopy and magnetic circular dichroism in codeposited C60–Co films with giant tunnel magnetoresistance Original Research Article
Chemical Physics Letters, Volume 470, Issues 4-6, 5 March 2009, Pages 244-248
Yoshihiro Matsumoto, Seiji Sakai, Yasumasa Takagi, Takeshi Nakagawa, Toshihiko Yokoyama, Toshihiro Shimada, Seiji Mitani, Hiroshi Naramoto, Yoshihito Maeda
Electronic and spin states of the codeposited C60–Co films with large tunnel magnetoresistance (TMR) effect were investigated with the X-ray absorption and magnetic circular dichroism (MCD) spectroscopies. It is revealed that a C60–Co compound generated in the C60–Co films shows the clear MCD signal attributed to the spin-polarized Co 3d states hybridized with C60 π orbitals. The magnetic response of these Co 3d-derived states agrees well with temperature dependence of the observed MR ratios of the granular C60–Co films. This suggests the incorporation of the spin-polarized Co 3d-derived states of the C60–Co compound into the observed TMR effect.

Temperature dependence of the giant magnetoresistance in Fe–Cr multilayers—Intralayer and interlayer exchange energies Original Research Article
Journal of Magnetism and Magnetic Materials, Volume 323, Issue 5, March 2011, Pages 646-649
R.S. Patel, A.K. Majumdar
We present field and temperature dependence data on giant magnetoresistive (GMR) ion-beam sputtered Fe–Cr multilayers of varying Cr thickness. We show that the decrease in GMR with temperature is related to the decrease in sublattice magnetization due to thermal excitation of magnons in the antiferromagnetic configuration. The intralayer and the interlayer exchange energies thus obtained vary systematically as the Cr thickness increases. The corresponding decrease in the measured saturation field further supports our interpretation leading to a better understanding of the physics of GMR.
Keywords: GMR; Fe-Cr multilayers; Exchange energies

Erratum to ‘X-ray absorption spectroscopy and magnetic circular dichroism in codeposited C60–Co films with giant tunnel magnetoresistance’ [Chem. Phys. Lett. 470 (2009) 244]
Chemical Physics Letters, Volume 474, Issues 1-3, 25 May 2009, Page 238
Yoshihiro Matsumoto, Seiji Sakai, Yasumasa Takagi, Takeshi Nakagawa, Toshihiko Yokoyama, Toshihiro Shimada, Seiji Mitani, Koki Takanashi, Hiroshi Naramoto, Yoshihito Maeda
Refers to: X-ray absorption spectroscopy and magnetic circular dichroism in codeposited C60–Co films with giant tunnel magnetoresistance
Chemical Physics Letters, Volume 470, Issues 4-6, 5 March 2009, Pages 244-248,
Yoshihiro Matsumoto, Seiji Sakai, Yasumasa Takagi, Takeshi Nakagawa, Toshihiko Yokoyama, Toshihiro Shimada, Seiji Mitani, Hiroshi Naramoto, Yoshihito Maeda

Magnetic instability of giant magnetoresistance spin-valves due to electromigration-induced inter-diffusion Original Research Article
Thin Solid Films, Volume 517, Issue 18, 31 July 2009, Pages 5557-5562
Jing Jiang, Seongtae Bae, Hojun Ryu
Electromigration-induced magnetic failures in NiFe/(Co)/Cu/(Co)/NiFe spin-valve (SV) multilayers have been investigated. Electrically stressed NiFe/Cu/NiFe SV multilayers showed a dramatic reduction of magnetic moment up to 41%, and a shift of interlayer coupling characteristics, while no obvious magnetic degradation was observed in the NiFe/Co/Cu/Co/NiFe SV multilayers. It was experimentally confirmed that the magnetic degradation of the NiFe/Cu/NiFe SV multilayers is primarily due to the formation of Ni–Cu intermixing caused by the electromigration-induced Cu spacer inter-diffusion. Furthermore, it was demonstrated that an ultra thin Co diffusion barrier at the NiFe/Cu interface is promisingly effective to improve the magnetic stability of NiFe/(Co)/Cu/(Co)/NiFe SV multilayers against electromigration.
Keywords: Magnetic instability; GMR spin-valve multi-layers; Electromigration-induced failures; Cu spacer inter-diffusion

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