Giant Magnetoresistance Materials Research Articles

Research and Application on GMR Current Sensing Technology

With the development of smart grid, and ever-increasing kinds of electrical loads, the power system requires current measurement technology with wider measurement range, this thesis designs a new type of current sensor based on Giant magnetoresistance (GMR) material. Firstly, this thesis introduces principles and characteristic of GMR current sensor. For the shortcomings of low sensitivity and poor linearity of GMR chip, this thesis presents a structure of open-loop current sensor using GMR chip as magnetic probe, which improves the sensitivity of sensor effectively. Based on the open-loop GMR current sensor structure, a closed-loop GMR current sensor design is proposed. This design compensates the magnetic field through the feedback circuit and improves the accuracy and dynamic measurement range of GMR current sensor. Finally, we tested the GMR sensor system we developed, include DC characteristic test and AC characteristic test, it shows the current sensor has the capability of high dynamic current measurement.

GIANT MAGNETORESISTANCE (GMR): SPINNING FROM RESEARCH TO ADVANCED TECHNOLOGY

In this paper, we aim to examine the research and development of materials demonstrating the giant magnetoresistance (GMR) property, a novel material property that has revolutionalised the advances of magnetic sensor and mass-memory technology today. A comprehensive outline for the fundamental materials aspects as well as the physics of the underlying mechanisms behind the GMR property is given. Recent development of GMR materials in data storage industry and other potential technological applications exploiting the GMR property are also discussed.

Laser ablation synthesis of C–Si–H-doped Co1–xO with novel (hkl)-specific paracrystal, Co interlayer and lattice shuffling

C–Si–H-doped Co1–xO particulates/nanocondensates of rocksalt-derived types were formed by pulsed laser ablation of metallic Co plate in tetraethyl orthosilicate and characterized by X-ray/electron diffraction and vibrational/optical spectroscopy. Such crystals were found to contain (001) paracrystal plate having defect cluster periodicity ca. 2.5 times that of the host lattice, and 1D 3x and 5x{111} commensurate superstructures along with (111) (Co/CoO) n multilayer. The (Co/CoO) n multilayer by (111)-specific faulting and oxygen diffusion is of interest to the synthesis of cermet, in particular giant magnetoresistance material, whereas the overall substances with characteristic vibration modes, binding energy and UV–visible absorptions (3.1 and 3.7 eV) may have potential optocatalytic applications.

Giant magnetoresistance in the cluster glass regime of Co-Ga alloys

A detailed study of low temperature electrical transport properties of CoxGa100−x (x = 54, 55.5, 57) alloy has been carried out. The origin of the resistivity anomalies and correlation between magnetic and electrical transport properties are identified through an elaborate analysis. The weak localization and enhanced electron-electron interaction effects partially support the electrical transport properties of the system. Further, the observed magnetoresistance can be well represented by localized model along with quantum corrections. The low temperature magnetoresistance value near critical composition is comparable to that reported in giant magnetoresistance materials.

Development of Giant Magnetoresistance Material Based on Cobalt Ferrite

Development of Giant Magnetoresistance Material Based on Cobalt Ferrite

Construction and validation of simple magnetic nanoparticle detector based on giant magnetoresistive effect

The finding of giant magnetoresistive(GMR) effect develops a new field for the sensing application with magnetic nanoparticles(MNPs) labeling. A convenient GMR sensor was built with a permanent magnet to excite the MNPs in this work. The sensing element contained a Wheatstone bridge with the GMR material as one of its branches. The magnetic field from MNPs unbalanced the Wheatstone bridge. After being amplified, the output signals were recorded. The construction and optimization of the magnetoresistive sensing platform were discussed in detail. The detection of three kinds of MNPs validated the performance of the proposed GMR sensor. The sensor showed a fast response to the addition or removal of MNPs. Because of its simplicity, this kind of GMR sensor can be developed in a routine laboratory. The finding of this new GMR sensor will promote the development of the method of probing biomolecules and the study on the biomolecular interaction after being labeled magnetically.

Thin Film of Giant Magnetoresistance (GMR) Material Prepared by Sputtering Method

In recent decades, a new magnetic sensor based on magnetoresistance effect is highly researched and developed intensively. GMR material has great potential as next generation magnetic field sensing devices. It has also good magnetic and electric properties, and high potential to be developed into various applications of electronic devices such as: magnetic field sensor, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory. GMR material can be developed to be solid state magnetic sensors that are widely used in low field magnetic sensing applications. A solid state magnetic sensor can directly convert magnetic field into resistance, which can be easily detected by applying a sense current or voltage. Generally, there are many sensors for measuring the low magnetic field, such as: fluxgate sensor, Hall sensor, induction coil, GMR sensor, and SQUID sensor. Compared to other low magnetic field sensing techniques, solid state sensors have demonstrated many advantages, such as: small size (<0.1mm2), low power, high sensitivity (~0.1Oe) and good compatibility with CMOS technology. The thin film of GMR is usually prepared using: sputtering, electro deposition or molecular beam epitaxy (MBE) techniques. But so far, not many researchers reported the manufacture of thin film of GMR by dc-Opposed Target Magnetron Sputtering (dc-OTMS). In this paper, we inform the development of GMR thin film with sandwich and spin valve structures using dc-OTMS method. We have also developed organic GMR with Alq3 as a spacer layer.

A Feedback Spin-Valve Memristive System

We propose theoretically a generalized memristive system based on controlled spin polarizations in giant magnetoresistive material using a feedback loop with classical Hall Effect. The dynamics can exhibit a memristive pinched hysteretic loop while it possesses a self-crossing knot not located at the origin. Additionally, a single-looped orbit can also be observed in the system. We provide a sufficient condition for the stability based on an estimation of the Floquet exponent. The analysis shows that the non-origin-crossing dynamics is generally permitted in a class of passive memory systems that are not subject to Ohm's Law. We further develope the prevailing homogeneous definition to a broadened concept of generalized heterogeneous memristive systems, permitting the self-crossing knot not located at the origin, and ultimately to the concept of compound memory electronic systems.

Study of Optical Band Gap of CuO Using Fermi's Golden Rule

Quantum size effect where the electronic and optical properties of solids are altered due to changes in the band structures, enhanced the surface/volume ratio in nano dimensions forces more than 33% of the atoms to be on the surface (for 10nm dot 35), which drastically altering the physical properties such as having lower melting temperature and lower sintering temperature, and higher diffusion force at elevated temperatures. Consequently, its Fermi's golden rule analysis becomes crucial. Cupric oxide (CuO) is an important transition metal oxide with the basis of several high temperature superconductors and giant magnetoresistance materials. In present investigation, optical Band Gap from UV data using Fermi's golden rule for single step chemically synthesized CuO was computed.

Development of Sensors Based on Giant Magnetoresistance Material

In this review we discuss development of sensors based on giant magnetoresistance (GMR) material.The GMR material has high magnetic and electrical properties, therefore it has great potential as next generation magnetic field sensing devices. During the last decade, intensive research efforts have been expended to develop sensors based on giant magnetoresistance (GMR) material, both based on inorganic materials and organic materials. Many application of GMR sensor, such as: current sensor, linear and rotational position sensor, head recording, and biosensor, are reviewed.

GMR Sensors: Technologies and Medical Applications

Giant Magnetoresistance (GMR) is a quantum mechanical effect found in thin film materials that are composed of alternating nano-size ferromagnetic and non magnetic layers. When a GMR material is in the presence of a magnetic field a change in electrical resistance is observed. The GMR effect has been used to produce magnetic sensors that can be used in a variety of applications. Although there are some sensors that have greater sensitivity and lower magnetic detection limits, GMR sensors have more commercial potential due to their small size, low power use, low fabrication cost, and their reproducible operation in very narrow magnetic ranges. The medical field is rapidly adopting the use of GMR magnetic sensors for many medical applications; this is leading to an increase in the number of patents that include GMR sensors. Two of the most promising medical application areas for GMR sensors are medical diagnostics and implant communication. This article reviews the GMR mechanism, measurement, fabrication techniques, and discusses a variety of medical applications and patents that incorporate GMR sensors. Keywords: GMR Sensors, Bioassays, Biosensors, Giant Magnetoresistance, Implant Communication, Magnetic Immunoassays, Magnetic Labeling, Magnetic Relaxation, Magnetic Sensor, Magnetic Sorting, Magnetic Switching, Magnetic Thin Films, Nanowires, Near Field Communication, Multilayer Nanowires

Magnetic and Electrical Transport Properties of Double Perovskite Sr2FeMoO6 Prepared by Sol‐Gel Method

With activated carbon for reducing agent, the sol‐gel method was used to prepare the giant magnetoresistance materials Sr2FeMoO6, which is the double Perovskite oxide. The structure, morphology, magnetic and electrical transport properties were investigated respectively by x‐ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The as‐synthesized sample is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group and unit cell parameter is a = 5.580Å, c = 7.882Å. The primary particles are spherical in shape and the grain size is below 100 nm. The curie temperature is above room temperature and the saturation magnetization is 13.321 A·m2/kg under 1.0 T at room temperature. The sample exhibit typical semiconductor behavior and the conductive mechanism can be described by small polaron variable range hopping model. The room temperature magnetoresistance of the sample under 1.0 T field is up to ‐10.02%. Moreover, it is found the dosage of citric acid and the amount of reducing agent has great effect on the phase structure and magnetic properties of the samples.

Biosensor Based on Giant Magnetoresistance Material

In recent years, giant magnetoresistance (GMR) sensors have shown a great potential as sensing elements for biomolecule detection. The resistance of a GMR sensor changes with the magnetic field applied to the sensor, so that a magnetically labeled biomolecule can induce a signal. Compared with the traditional optical detection that is widely used in biomedicine, GMR sensors are more sensitive, portable, and give a fully electronic readout. In addition, GMR sensors are inexpensive and the fabrication is compatible with the current VLSI (Very Large Scale Integration) technology. In this regard, GMR sensors can be easily integrated with electronics and microfluidics to detect many different analytes on a single chip. In this article, the authors demonstrate a comprehensive review on a novel approach in biosensors based on GMR material.

Dependence of Magnetization on Temperature, Magnetoresistance Effect and Magnetic Phase Diagram for the Layered Gd5Ge4 Compound

The dependence of dc magnetization and electrical transport on temperature were systemically studied for the layered Gd5Ge4 compound. A complex coexistence behavior of ferromagnetism (FM) with antiferromagnetism (AFM) phase and significant magnetoresistance effect were found under the inducement by the applied magnetic field. The results show an unusual magnetoresistance (MR) effect with opposite behavior at the high and low temperatures, which is positive at high temperature region and negative at low temperature region for the layered Gd5Ge4 alloy. And its MR maximum is close to 50%, which can be a very large numerical value e.g. for giant magnetoresistance (GMR) materials. From the magnetization loop under different temperatures, also a magnetization step behavior was found below ∼6.2 K. The results proved an existence of reentrance AFM phase at low temperature. From experimental data, also the magnetic phase diagram is obtained. This kind of complex magnetization is analyzed and discussed in the frame of phase separation. The experimental results opened also the possibility of application of the layered Gd5Ge4 compound in the fields of information record and sensor technique.

Giant magnetoresistance in composites of organic polymers with manganese acetylacetonate and lanthanum-praseodymium chlorides exhibiting ionic conductivity

We present a new giant magnetoresistance (GMR) material composed of polyaniline, polystyrene, sulfur, manganese acetylacetonate, lanthanum, and praseodymium chlorides. These compounds were mixed and processed mechanochemically to obtain thin films. External magnetic field of 6000 Oe increases conductivity of films by more than 300%. Analysis of transient current kinetics after application of constant voltage (10 V) to samples showed the existence of three types of charge carriers, which we identified as e−, H+, and Cl−. Contribution of functional groups of polyaniline and elemental sulfur S in the formation of the above charge carriers in this new GMR composite material is discussed.

Modelling the sensitivity of infrared emissivity of magnetic thin films to giant magnetoresistance

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.

Large anisotropy of spin polarization in Heusler alloy Ni2MnGa induced by martensitic transformation

Spin polarization both in the cubic austenitic and tetragonal martensitic phases of the Ni2MnGa alloy has been investigated using first-principles calculations combined with classical Bloch–Boltzmann transport theory. It is shown that the degree of spin polarization, while decreasing from 42% in the ⟨001⟩ directions of the austenitic phase to 30% in the [100] direction of the martensitic phase, rises to 75% in the [001] direction of the martensitic phase, resulting from a preferential reconstruction of the spin-down Fermi surfaces upon martensitic transformation. With this finding, various recent intriguing electrical measurements upon Ni2MnGa across the martensitic transformation can find an explanation. This also opens a way of searching for giant magnetoresistance materials.

Substitution induced B-cation ordering in solid oxide fuel cell ceramics: (La 0.8Sr 0.2)(M 0.9Ni 0.1)O 3 (M = Mn, Cr)

Perovskites are important materials in a number of important technological applications, including solid oxide fuel cells, catalysis, and giant magneto-resistance materials. For many of these purposes, a mixture of B-cations can be used to tune the desired properties, e.g., oxygen reduction, ionic conductivity. For a solid oxide fuel cell, two particular ceramic components are of critical importance and have been extensively studied, the cathode (La 0.8Sr 0.2)MnO 3− x and the interconnect material (La 0.8Sr 0.2)CrO 3. In this study, we examined the mixed B-cation perovskites (La 0.8Sr 0.2)(M 0.9Ni 0.1)O 3 (M = Mn, Cr). All materials were synthesized using the glycine-nitrate method, followed by air annealing. The structures were determined using powder neutron diffraction methods. Refinement of the data showed that even at this low concentration, the compounds have monoclinic symmetry ( P2 1/ n) and that the nickel had a strong preference for the smaller of the two octahedral sites. This small amount of nickel substituted on the B-site resulted in a symmetry reduction when compared to the unsubstituted (LaSr)MnO 3 or (LaSr)CrO 3 materials. Although this structural type has been seen previously in heavily substituted perovskites, these materials show that even at this low level of substitution a segregation of the metals in a manner similar to the double perovskites A 2BB′O 6− x can be detected. This may have implications involving material stresses on cycling that may result as the temperature is raised or lowered through this crystallographic transition.

Theoretical and experimental investigation on giant magnetoresistive materials with amorphous ferromagnetic layer

Pseudo-spin-valve (PSV) sandwiches using amorphous CoNbZr alloy as soft magnetic layer were fabricated by magnetron sputtering. The giant magnetoresistance (GMR) and its dependence on the thickness of magnetic layer were investigated. Anti-parallel magnetization alignments were observed in the samples with very thin CoNbZr thickness (2–4 nm) and a maximum GMR ratio of 6.5% was obtained. The Camley-Barnas semiclassical model was extended for amorphous layer based magnetic sandwiches by considering that the mixed layers exist between the ferromagnetic and nonmagnetic layer. The calculated results agree with the experimental results very well, indicating that the new model gives a more realistic picture of the physical processes that take place in the magnetic sandwiches. Moreover, the calculated results for amorphous sandwiches also clarify that the occurrence of maximum GMR at very small thickness of amorphous layer is ascribed to the short mean-free-path in amorphous materials.

Design and Development of Magnetic Sensors Based on Giant Magnetoresistance (GMR) Materials

This paper describes magnetic sensors that have been developed in the last three years. GMR thin film materials have been successfully developed using unpinned CoFe/Cu/CoFe sandwiches on Si(100) substrate using a home built dc-opposed-target magnetron sputtering (OTMS). The magnetization of the sandwich is measured using hysteresis loop instrument, the Vibrating Sample Magnetometer (VSM). It was found that the phase of GMR was formed, with the MR ratio 15.76%.