Dependence Of Giant Magnetoresistance Research Articles

Size evolution of nanomagnetic particles and magnetotransport properties of (Co90Fe10)20Ag80 nanogranular films: influence of Cu80Ag15Au5 underlayer

The influence of (Co90Fe10)20Ag80 film thickness and of Cu80Ag15Au5 underlayer on nanomagnetic, magnetotransport and structural properties of (Co90Fe10)20Ag80 nanogranular films prepared by ultra-high vacuum ion beam sputtering technique have been investigated using X-ray diffraction, X-ray reflectivity and vibrating sample magnetometer. Films indicate a superparamagnetic behavior. The evolution of the magnetic particle size in (Co90Fe10)20Ag80 film with different thicknesses was calculated by fit of magnetization curves using Langevin equation. A parallel resistance model has been used to determine particle size distribution. The average (mean) particle sizes range from 1.6 to 2.1 nm. A linear dependence of giant magnetoresistance (GMR) on the particle size has been found. This result is also supported by the observed linear correlation between the square root of the effective magnetization and the particle size. Furthermore, a linear correlation between the square of GMR and the distance between particles has been found. This remains unchanged also in (Co90Fe10)20Ag80 films with Cu80Ag15Au5 underlayer. Using of the underlayer leads to an enhancement of the mean particle size (1.8–2.5 nm) and GMR; however, to a reduction of distances between particles accompanied by the destruction of the 〈111〉 texture in the Ag matrix structure. The reason of the GMR effect in the nanogranular films is discussed by means of the obtained results.

Growth and characterisation on giant magnetoresistance property of metallic multilayers

Metallic multilayers with specific materials configurations have been shown to exhibit giant magnetoresistance effect at room temperature. In this study, microstructural analysis was carried out on magnetron sputtered Co/Cu multilayers using various diffraction and imaging techniques. Dominant characteristic features associated with the multilayers, such as lateral and vertical columnar grain orientations as well as layer undulation and regularity were identified. By deliberately introducing microstructural changes using a buffer layer and via heat treatment, detailed microstructural analysis carried out on the multilayers has provided an insight into the dependence of giant magnetoresistance on the observed microstructures. The present study shows that high giant magnetoresistance effect of the multilayers was associated with highly correlated interfacial profiles, sharp columnar grain boundaries and high degree of lateral coherency in columnar grain growth. While the introduction of iron buffer layer favoured the growth of these structural features that were responsible for large giant magnetoresistance effect, annealing led to deterioration of giant magnetoresistance property of the multilayers.

Thickness Dependence of Giant Magnetoresistance in Spin Valves: Influence of Interface and Bulk Scattering

Using the semiclassical Boltzmann theory, we have investigated the influences of pure interface, nonpure interface, bulk, and interface plus bulk scattering on the giant magnetoresistance (GMR) dependence on layer thickness of the bottom spin valve (BSV), synthetic antiferromagnetic (SAF) spin valve, and dual spin valve (DSV). Our work shows consistency with experiment and theory and may provide some useful guidelines for electrical and structural optimizations of spin valves

Withdrawal: Dependence of giant magnetoresistance on the thicknesses of magnetic and nonmagnetic layers in dual spin valves [phys. stat. sol. (a) 201, 2995 (2004)]

AbstractThe authors withdraw their article published in phys. stat. sol. (a) 201, 2995 (2004). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of giant magnetoresistance on the thicknesses of magnetic and nonmagnetic layers in dual spin valves

Based on a previous semi-classical model, we investigated the giant magnetoresistance (GMR) as functions of the thicknesses of the outer and center ferromagnetic layers and the nonmagnetic layer in dual spin valves. The calculated GMR was found to be consistent with experimental results, indicating that our model is applicable even for complicated dual spin valve multilayers. Moreover, some theoretical predictions are given in this letter that allow us to propose ways to optimize dual spin valve structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Giant magnetoresistance and microstructure of FeCo–Al 2 O 3 nanogranular films

The giant magnetoresistance (GMR) and microstructure of FeCo-Al 2 O 3 films sputtered at various substrate temperatures (T s ) were investigated. The results indicate that the GMR of as-sputtered FeCo(41 vol.%)-Al 2 O 3 granular films reaches the peak value of 6.9%, while for FeCo-Al 2 O 3 granular films sputtered at 473 K, the dependence of GMR on volume fraction (f v ) displays 6% peak value with lower content about 35 vol.% FeCo. Based on the features of GMR of FeCo-Al 2 O 3 granular films sputtered at different f v and T, an optimum factor A(D c /L c ) is introduced to explain qualitatively the influence of spin-dependent interface scattering(D) and tunneling barrier's thickness(L) related to f v and Ts on GMR. The phase separation of hcp α-Co from bcc α-Fe (Co) was revealed by analytical electron microscopy and its effect on GMR for different f v and T s was discussed.

Dependence of giant magnetoresistance of electrodeposited multilayers on the number of layers

Dependence of giant magnetoresistance of electrodeposited multilayers on the number of layers

Giant Magnetoresistance in Co-Cu/Cu Multilayers Prepared by Various Electrodeposition Control Modes

The giant magnetoresistance (GMR) effect was studied on electrodeposited Co-Cu/Cu multilayers of 300 bilayer repeats which were produced in an electrochemical cell with homogeneous current distribution from a bath with two solutes The preparation employed the conventional potentiostatic/potentiostatic and galvanostatic/galvanostatic, as well as an unprecedented galvanostatic/potentiostatic (G/P) control. We find that the specific deposition parameters rather than the deposition mode itself are decisive for the magnitude of the GMR which could be as high as 10% measured at 1 kOe on substrate-free multilayers in optimized G/P conditions. For this new deposition mode, detailed studies on the dependence of GMR on Co and Cu layer thicknesses as well as the bath pH were performed. No oscillatory behavior of the GMR as a function of the Cu layer thickness could be observed. The results suggest the importance of a Co-dissolution and/or a Co vs. Cu exchange reaction after completing the deposition of each magnetic layer. These reactions lead to the formation of a Cu or Cu-rich interface layer prior to the electrochemical deposition of the actual Cu layer during the subsequent pulse in either deposition mode. It turned out that the properties of this interfacial layer (thickness, degree of chemical intermixing) strongly influence the resulting GMR behavior of the multilayer. © 2003 The Electrochemical Society. All rights reserved.

Giant magnetoresistance effect of Co–TbN macroscopic ferrimagnets

A new macroscopic ferrimagnet Co–TbN has TbN precipitates in a Co matrix. The Co–TbN system shows the typical magnetic properties of a macroscopic ferrimagnet which are a magnetic compensation point and negative giant magnetoresistance (GMR). The Co–TbN mixture with 32 mole % TbN exhibits 0.72% GMR in fields up to 8 kOe at room temperature and 9% GMR at 250 K in 40 kOe. In the Co–TbN system, the dependence of GMR with temperature is quite different from that of previously studied GMR materials that have magnetoresistance decreases with increasing temperature. The GMR effect in the Co–TbN system increases with increasing temperature, because of the increase of ferromagnetic alignment of Co and TbN in a field at higher temperature.

Nanocomposite with Non-Spherical Granules – Logarithmic Field Dependence of Giant Magnetoresistance

ABSTRACTMagnetoresistance of the nanocomposite Fex(SiO2)1−x (x≍0.6) at high enough magnetic field is logarithmic function of the magnetic field. Such a dependence does not fall into the known theory of giant magnetoresistance of ferromagnetic nanocomposites. This paper examines the giant magnetoresistance of such a system in terms of a simple model where the non-ordinary quasi-logarithmic magnetic field dependence of nanocomposite magnetoresistance is related to the non-spherical granules' distribution over their shapes.

The study on the giant magnetoresistance in magnetic granular alloys

To study the giant magnetoresistance in magnetic granular alloys, an effective cluster model is extended to include spin-dependent interface scattering and bulk scattering. The dependence of giant magnetoresistance on particle size and volume fraction of magnetic component is discussed, some features of the giant magnetoresistance observed in recent experiments can be explained and the optimal choice of parameters to maximize the giant magnetoresistance can be determined.

Dependence of giant magnetoresistance on the thickness of magnetic and non-magnetic layers in spin-valve sandwiches

We have performed the calculations of giant magnetoresistance (GMR) versus the thickness of ferromagnetic and/or non-magnetic layers in NiFe/Cu/NiFe and/or Co/Cu/Co sandwiched structures in both cases: (1) interfacial spin-dependent scattering only; (2) the presence of both interfacial and bulk spin-dependent scattering. The results show that, in the presence of both interfacial and bulk spin-dependent scattering, the dependence of the calculated GMR on ferromagnetic and/or non-magnetic thickness is consistent with the experimental results. The comparison of the calculated results in both cases demonstrates the importance of bulk spin-dependent scattering in Co/Cu and/or NiFe/Cu systems. Furthermore, the calculations indicate that the ferromagnetic thickness corresponding to the GMR maximum increases with the increase of the thickness of non-magnetic layer in NiFe/Cu/NiFe and/or Co/Cu/Co sandwiches.

EFFECT OF SPIN-FLIP SCATTERING ON CURRENT-IN-PLANE MAGNETO-TRANSPORT IN MAGNETIC MULTILAYERED STRUCTURES WITH ARBITRARY MAGNETIZATION ALIGNMENTS

By a quantization-axis transformation, we derive an extended equation which Green's function satisfies in the presence of spin-flip scattering, and then apply the Kubo formula to study the variation of the giant magnetoresistance (GMR) in magnetic multilayered structures with the angle θ between the magnetizations of succesive magnetic films. It is found that in the presence of spin-flip scattering and spin-dependent potential barriers, the linear dependence of GMR on sin 2(θ/2) can be approximately obtained, which is qualitatively consistent with the experimental result.

Microstructure, magnetic properties and giant magnetoresistance of granular Cu-Co alloy

The microstructure in a granular Cu88Co12 alloy was investigated by means of x-ray diffraction (XRD), a field ion microscope with atom probe (AP-FIM) and a field emission gun-transmission electron microscope (FEG-TEM) with energy dispersive x-ray spectroscopy (EDS). Giant magnetoresistance (GMR) and magnetic properties were studied to clarify the relationship between the GMR, magnetic properties and microstructures. The morphology of nanometre-sized cobalt granules within the grains were directly determined utilizing AP-FIM and FEG-TEM with EDS. Most cobalt granules are spherical and some others are plate-like in shape. GMR was observed in alloys with an average granule size ranging from 1.5 to 6 nm in diameter. TEM investigations showed that larger Co-rich precipitates formed at grain boundaries. The magnetic properties of the granular alloy were interpreted using the microstructure information and the dependence of GMR on magnetization was discussed.

Interfacial roughness and angle dependence of giant magnetoresistance in magnetic superlattices

Using the two-point conductivity formula, we numerically evaluate the giant magnetoresistance (GMR) in magnetic superlattices with currents in the plane of the layers (CIP), from which the effect of the interfacial roughness and magnetization configuration on the GMR is studied. With increasing interfacial roughness, the maximal GMR ratio is found to first increase and then decrease, exhibiting a peak at an optimum strength of interfacial roughness. For systems composed of relatively thick layers, the GMR is approximately proportional to $${\cos ^2}\theta $$ ,where $$2\theta $$ is the angle between the magnetizations in two successive ferromagnetic layers, but noticeable departures from this dependence are found when the layers become sufficiently thin.

Giant magnetoresistance in bulk materials

Employing different types of decomposition the dependence of giant magnetoresistance (GMR) on the interplay between spin-dependent scattering at second phase particle interfaces and their presence as isotropically or anisotropically oriented scattering sites has been studied by comparing: (1) dispersions of Co clusters embedded in Cu, (2) a lamellar eutectic consisting of alternating stacking of Co and Au-rich lamellae and (3) spinodally decomposed and aligned ferromagnetic particles in AlNiCo5 and FeCrCo. In melt-spun Cu100−xCox the Co concentration has been varied from x = 0 up to the three dimensional percolation limit for an fcc lattice. A transition from anisotropic magnetoresistance (AMR) to GMR was observed for x < 2 at.%. GMR behavior dominates for x ≥ 2 at.% with a maximum amplitude of 35% at 10 K and 7% at 293 K. In Au71.6Co28.4 the GMR effect is only 1.4% at 300 K and 2.8% at 10 K, but it is linked to the multilayer like eutectic microstructure. GMR amplitudes in AlNiCo5 at 16 T sizes as much as 6.5% at 10 K and 4.25% at 300 K and depend on the direction of the current with respect to the aligned ferromagnetic particles. The probability of magnetic scattering is two times more likely when the current is applied perpendicular to the direction of the particle elongation. A transition from AMR to GMR is observed for FeCrCo upon annealing.

Angular dependence of giant magnetoresistance in a superlattice.

Most discussions of giant magnetoresistance (GMR) have focused on collinear cases where the magnetizations in adjacent layers are either parallel or antiparallel. To explore the relative importance of the superlattice potential and of the impurity scattering on the angular dependence of GMR, we calculate the electrical resistivity for noncollinear magnetizations. The electronic structure of the superlattice is modeled by a Kronig-Penney potential. When the magnetizations of the adjacent layers are neither parallel nor antiparallel, spinor forms of Bloch states and dispersion relations are derived. Then the conductivity as a function of the angle between magnetization directions of adjacent layers is calculated in the homogeneous limit where the mean free path is much larger than the layer thickness. We find the angular dependence of the resistivity and hence of the GMR for current in the plane of layers and perpendicular to the plane of the layers depends on the spin-dependent superlattice potential, and the details of the scattering potential. \textcopyright{} 1996 The American Physical Society.

Dependence of giant magnetoresistance on microstructures in ion-beam co-sputtered CoxAg1?x granular films

A number of structural analysis methods were employed to investigate the microstructures of ion-beam co-sputtering of CoxAg1−x (0⩽x⩽100 at%) granular films. Forx=22 at%, the sample which has the optimal giant magnetoresistance at room temperature, there exists either crystallized or highly disordered regions shown by high-resolution electron microscopy. At the boundary between cobalt granules and the silver matrix, lattice mismatch was formed, leading to roughness of the interfaces. X-ray diffraction and transmission electron microscopy revealed that the samples had f c c structure at lowx, with (111) texture, and the h c p structure gradually appeared as x>75 at %. Relative lattice expansion was observed asx increased.

Giant Magnetoresistance in Magnetic Nanostructures

This chapter contains a brief review of the giant magnetoresistance (GMR) effect exhibited by magnetic multilayers, granular alloys, and related materials. Subjects covered include a description of the phenomenon, and the related oscillatory interlayer exchange coupling in magnetic multilayers; a simple model of giant magnetoresistance; the inverse GMR effect in spin-engineered magnetic multilayers; structures that display large changes in resistance in small magnetic fields, possibly for use in magnetic field sensors; and the dependence of GMR on various aspects of the magnetic structures.

Dependence of giant magnetoresistance on the number of valence electrons in the ferromagnetic constituent of granular alloys: Precipitates of face-centered cubic Fe–Co, Co–Ni, and Ni–Cu alloys in Ag matrices

The dependence of giant magnetoresistance on the composition of ferromagnetic face-centered cubic precipitates in an Ag matrix grown epitaxially on MgO {100} is described. These compositions were chosen from the alloy ranges Ni0.6Cu0.4→Ni→NixCo1−x→ Co→Fe0.2Co0.8 to give a number of valence electrons per atom, n=n3d+n4s, in the ferromagnetic precipitates that ranged from 8.8 to 10.4. This corresponds to a decrease of the saturation magnetization from ∼1500 emu/cm3 to approximately zero. To reduce the influence of other variables the concentration of the precipitates was kept constant (at 23.5 vol %) and their size approximately so. Corrections are applied to adjust for some remaining variation in precipitate size. With other factors held constant, there is a steady increase in both the magnetoresistance ratio and the magnetic-field-dependent resistivity with increase in the saturation magnetization of the alloys, i.e., with increase in the spontaneous magnetization of the single-domain precipitates.