Giant Magnetoresistance Properties Research Articles

The effect of NiFeCr seed layer composition on the giant magnetoresistance properties of [FeCoNi/Cu] multilayers

We present a systematic study on the giant magnetoresistance (GMR) and interlayer exchange couplings (IEC) in polycrystalline [Fe16Co66Ni18/Cu]5/Fe16Co66Ni18 multilayer films deposited on NiFeCr seed layers with various compositions. We observed that the GMR ratio (ΔR/R) depends on bilinear and biquadratic IEC coefficients, J1 and J2, and varies linearly with their ratio, J1/J2. The maximum ΔR/R of 35 ± 2.5% and strong antiparallel IEC (J1/J2 > 1) were observed for the seed layers with a particular Ni:Fe ratio of (Ni0.55Cr0.45)100-yFey with 0 ≤ y ≤ 47 at. %. Structural studies confirm that the high ΔR/R and J1/J2 for these NiFeCr compositions are related to a strong fcc [111] crystallographic texture and a coarse grain size of the FeCoNi/Cu mutilayers. In addition, we observed that the film deposited on a Ni32Fe33Cr35 seed layer showed a stronger [111] texture, but a lower ΔR/R (17%) than those deposited on a Ni36Fe51Cr13 seed layer (ΔR/R = 28%). Detailed microstructural analysis indicated an increased arithmetic average roughness (Ra) of the interfaces between FeCoNi and Cu layers for the films with the Ni32Fe33Cr35 seed layer. We argue that the lower ΔR/R in the film despite the relatively strong [111] texture is due to its higher Ra which causes a reduction in antiparallel IEC. This indicates that two conditions of (i) a strong [111] crystallographic texture and (ii) small interface roughness must be satisfied in the FeCoNi/Cu multilayer to achieve a strong antiparallel IEC and thus large ΔR/R.

Effects of interfacial roughness on the GMR of Ta/Co/Ta multilayers studied by neutron reflectometer

To study the effects of the roughness of magnetic nano-multilayer films on the giant magnetoresistance (GMR) performance, we used magnetron sputtering to prepare Ta/Co/Ta films with different Co thicknesses on a silicon substrate. The surface and interfacial roughness of the multilayer films were investigated using atomic force microscopy (AFM) and neutron reflectometry. The AFM results with a range of 10 μm indicated that the surface undulation increased with the increment of the Co thickness and the root-mean-square (RMS) roughness increased from 0.48 to 2.26 nm. The neutron reflectometry results proved that the thicker the Co layer, the rougher the interface in the multilayer film, with an increase from 1 to 2.7 nm. The four probe method was used to study the GMR properties of the films. It indicated that the GMR effect was enhanced and the GMR value shifted from − 0.04% to − 1.13% with increasing Co thickness from 6.5 to 20 nm. The enhancement in the GMR effect originated from the thicker Co layer, which led to increasing interfacial roughness, thereby enhancing the spin-dependent scattering of the interface and increasing the absolute value of the GMR. Nevertheless, when the Co thickness increased to 42 nm, the GMR absolute value decreased from 1.13 to 0.8% and the GMR effect was destroyed. This behavior originated from the increased shunt of the ferromagnetic layer and the rougher Ta capping layer increasing the spin-independent scattering center, thereby eventually undermining the GMR effect. Diffusion between the multilayer films was observed using a polarized neutron reflection experiment, further illustrating that the GMR effect could be adjusted by the interfacial roughness.

Two-Phase Co–Cu Thin Films with Size Distribution of Ferromagnetic Nanostructures Optimum for Giant Magneto Resistance

New thin-film microstructure, with a homogeneous distribution of a crystalized one phase Co-rich magnetic nanoparticles, embedded in a Cu-rich continuous paramagnetic matrix was obtained. This structure has many of the characteristics deemed optimal for Giant Magneto Resistance (GMR). These characteristics are; mean free path of the electrons in the matrix, granules/matrix interface roughness, the ferromagnetic concentration of the magnetic granules, and most importantly, the size distribution of the granules. This microstructure was created in Co-93at%Cu thin film, through spinodal decomposition after a short time of aging that reached equilibrium by a growth and coarsening process. Main goal of the present work was the enhancement of the microstructure in order to pinpoint the optimum microstructural and magnetic feature that improves the GMR sensitivity and stability in granular materials. Accordingly, Structural evolution of the thin films was controlled by the annealing time and temperature. Four-probe-technique was utilized to measure the GMR properties. GMR curve for a sample annealed at 150 °C was found to be stable and saturated even at low magnetic field (<5 kOe). Microstructural evolution and compositional analysis of the thin film was investigated using in-situ transmission electron microscopy (TEM) and the energy dispersive X-ray spectrometer (EDXS).

Thickness dependence of degree of B2 order of polycrystalline Co2(Mn0.6Fe0.4)Ge Heusler alloy films measured by anomalous X-ray diffraction and its impacts on current-perpendicular-to-plane giant magnetoresistance properties

We investigated the degree of B2 order (SB2) of 4-10 nm-thick polycrystalline Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy films using anomalous X-ray diffraction (AXRD) and its correlation to the magnitude of current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) effect. We found that SB2 of the CMFG films is degraded for the film thickness below 6 nm, which is an issue for practical applications of CPP-GMR devices such as read head sensors of hard disk drives. Since SB2 has a thickness-dependence, the bulk spin polarization (β) of the CMFG layers is also expected to vary depending on the thickness; thus, the deduction of β using the Valet-Fert model, where β is assumed to be thickness-independent, is not valid for these CPP-GMR devices.

Heterogeneous magnetism and kinetic arrest in antiperovskite Mn3−xNixGaC compounds with Ni2MnGa Heusler insertions

Mn-based antiperovskite compounds in the form ${\mathrm{Mn}}_{3}AX$, where $A$ is a main group element and $X$ is C or N, undergo magnetostructural transitions with which these materials acquire magnetocaloric, giant magnetoresistance, and spin-transport properties, which can be modified or tailored by manipulating the compositions of numerous compounds. This enables closer investigations and better understandings of the underlying principles governing these properties. ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Ni}}_{x}\mathrm{GaC}$, which is a derivative of the prototype ${\mathrm{Mn}}_{3}\mathrm{GaC}$ antiperovskite, would normally be expected to form a cubic structure with a homogeneous composition. Contrary to this, we find that the addition of Ni leads to a heterogenous compound consisting of an antiperovskite part and a ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ Heusler insertions. The system shows kinetic arrest features, which we study as a function of Ni composition using the techniques of x-ray diffraction, magnetization, and neutron diffraction under a magnetic field.

Magnetoelectric P(VDF-HFP)-CoFe2O4 films and their giant magnetoresistance properties

Abstract Magnetoelectric (ME) nanocomposite flexible films composed of electroactive poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) and ferromagnetic cobalt ferrite (CoFe2O4) are fabricated. Single-phase nano CoFe2O4 with cubic spinel structure, synthesized by sol-gel auto combustion technique, is reinforced in different weight percentages to fabricate P(VDF-HFP)-CoFe2O4 films through spin coating technique. Effect of CoFe2O4 on structural, morphological, magnetic, ferroelectric, magnetoelectric properties, and giant magnetoresistance (GMR) behavior has been investigated. It is observed that the reinforcement of CoFe2O4 in P(VDF-HFP) matrix has strongly influenced the formation of β-phase conformation and the degree of structural order. The co-existence of ferroelectric and ferromagnetic orderings in the films has been demonstrated by the P-E and M-H plots. The variations in the polarization effects in the presence of a magnetic field provide the evidence for magnetoelectric cross-coupling in P(VDF-HFP)-CoFe2O4. The films exhibit a GMR effect from 7% to 100%. In order to demonstrate the use of ME induced GMR in magnetic field sensing, P(VDF-HFP)-CoFe2O4 film (10 wt%) is used in a prototype sensor circuit. A good sensing ability and linear response obtained prove that the prepared film can be used as field sensor.

Characteristic features of the magnetoresistance in the ferrimagnetic (Sr2FeMoO6-δ) – dielectric (SrMoO4) nanocomposite

Magnetic metal-oxide compounds with high values of magnetoresistance (MR) have attracted huge interest for spintronic applications, among which Sr2FeMoO6-δ (SFMO) has been relatively less known compared to the cobaltites and manganites, despite 100% electrons spin-polarization degree and a high Curie temperature. Here, stable fabrication and systematic analysis of nanocomposites based on SFMO with SrMoO4 dielectric sheaths are presented. SFMO-SrMoO4 nanocomposites were fabricated as follows: synthesis of the SFMO single-phase nanopowders by the modified citrate-gel technique; compaction under high pressure; thermal treatment for sheaths formation around grains. The nanocomposite is observed to exhibit a transitional behavior of conductivity from metallic, which is characteristic for the SFMO to semiconductor one in the temperature range 4 – 300K under magnetic fields up to 10T. A negative MR is observed due to the spin-polarized charge carriers tunneling through dielectric sheaths. MR value reaches 43% under 8T at 10κ. The dielectric sheaths thickness was determined to be about 10 nm by electric breakdown voltage value at current-voltage characteristics curves. The breakdown is found to be a reversible process determined by collisional ionization of dielectric atoms in strong electric field depending on knocked-out electrons from the SrMoO4. It was found that MR changes sign in electric breakdown region, revealing the giant magnetoresistive properties.

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.

Effect of chemical composition and Co-core size on the magnetic and magneto-transport properties of CoyAg100−y core–shell nanocrystallites

ABSTRACTThis paper describes the applicability of a modified polyol process in conjunction with a transmetallation reaction in synthesis of CoyAg100−y nanocrystallites of a core–shell structure. The substitution Co → Ag is varied as 20 ≤ y ≤ 95 by tuning the microstructure with functional magnetic and giant magneto resistance properties. The existence of core–shell structures was confirmed through transmission electron microscope and the size of Co-core increased from 8 to 50 nm with decrease in Ag-content of the sample. The magnetic behaviour of the sample changed from a pseudo-superparamagnetic nature to ferromagnetic with increase in Co-core size. Normalised saturation magnetisation values increased from 89.5 to 128.6 emu/g with increase in size of Co-core; however, none of the ferromagnetic samples exhibited any magneto resistance (MR). A value of 2.0% MR was observed in case of Co20.6Ag79.4 which increased to a maximum of 3.6% MR for Co36.6Ag63.4 sample when measured at 5 K.

Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses

The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3nm to 10nm using electrodeposition. By now, the thinnest Cu (0.5nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current–time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of −0.3 and −1.5V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600kA/m from 3 to 8nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8nm of the CoFe layer thickness. It is seen that the thin Cu layer (fixed at 0.5nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance (GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices.

Perpendicular Giant Magnetoresistance and Magnetic Properties of Co/Cu Nanowire Arrays Affected by Period Number and Copper Layer Thickness

One-dimensional magnetic nanowires have attracted much attention in the last decades due to their unique physical properties and potential applications in magnetic recording and spintronics. In this work, ordered arrays of Co/Cu multilayered nanowires which can be exploited to develop magnetoresistive sensors were successfully prepared using porous anodic alumina (PAA) templates. The structure and morphology of the multilayered nanowire arrays were characterized by transmission electron microscopy and scanning electron microscopy. The nanowire arrays are highly ordered and the average diameter is about 50 nm, which is controlled by the pore diameter of the PAA templates. The influences of period number and Cu layer thickness on the magnetic and the giant magnetoresistance (GMR) properties were investigated. The coercivity and remanence ratio increase first and then gradually tend to be stable with the increase of period number and the Cu layer thickness, while the GMR ratio increases first and then decreases with the increase of the period number accompanied by an oscillatory behavior of GMR as the Cu layer thickness changes, which are ascribed to the spin dependence electron scattering in the multilayers. The optimum GMR of −13% appears at Co (50 nm)/Cu (5 nm) with 200 deposition cycles in our experimental conditions.

Effect of sub-layer thickness on magnetic and giant magnetoresistance properties of Ni–Fe/Cu/Co/Cu multilayered nanowire arrays

Ni–Fe/Cu/Co/Cu multilayered nanowire arrays were electrodeposited into anodic aluminum oxide template by using dual-bath method at room temperature. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology and structure of the multilayered nanowire arrays. Vibrating sample magnetometer and physical property measurement system were used to measure their magnetic and giant magnetoresistance (GMR) properties. The effect of sub-layer thickness on the magnetic and GMR properties was investigated. The results indicate that magnetic properties of electrodeposited nanowires are not affected obviously by Cu layer thickness, while magnetic layers (Ni–Fe and Co layers) have significant influence. In addition, GMR ratio presents an oscillatory behavior as Cu layer thickness changes. The magnetic and GMR properties of the multilayered nanowire arrays are optimum at room temperature for the material structure of Ni–Fe (25nm)/Cu (15nm)/Co (25nm)/Cu (15nm) with 30 deposition cycles.

Combinatorial Fe–Co thin film magnetic structures obtained by thermionic vacuum arc method

Magnetoresistive Fe–Co based thin film structures were produced using thermionic vacuum arc method. The purpose of this work was to obtain significant magnetic response on different granular combinatorial structures. The Giant Magnetoresistive (GMR) and combination between GMR and Tunneling Magnetoresistive (TMR) properties of the thin film structures were the aim of the work. The proposed method in order to obtain the desired granular structures is based on electron beam emitted by an externally heated cathode, accelerated by a high anodic potential.The work consisted in preparing two sets of samples, first being a combination between Fe–Co as magnetic materials embedded in a Cu matrix, with a total thickness of 200nm. The second structure was a combination between Fe–Co (50%–50%) alloy, embedded in a matrix of Cu combined with MgO with a thickness of 200nm. Both sets of samples were obtained by three simultaneous types of discharges. Because of the substrate positioning in respect with the three anode–cathode systems, different material concentrations were obtained, confirmed by Energy Dispersive Spectroscopy (EDS) measurement results. Structural and morphological properties were investigated using Scanning Electron Microscopy; Atomic Force Microscopy and EDS. Electrical properties of the obtained samples were studied using the 4 point measurement method. The magnetic properties were first studied using a non-destructive optical method called MOKE (Magneto-Optical Kerr Effect). Electrical resistance behavior of the granular type structures was studied for different values of the magnetic field, up to 0.3T, at different values of the sample temperature. The magnetoresistive effect obtained for the two sets of samples varied from 1.5% to 81% in respect with the substrate positioning and sample temperature for a constant magnetic field.

Extensive study of giant magnetoresistance properties in half-metallic Co2(Fe,Mn)Si-based devices

Fully epitaxial Co2FexMn1−xSi(CFMS)/Ag/Co2FexMn1−xSi current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses tCFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and tCFMS = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives.

Giant Magnetoresistance in Electrodeposited Films: Current Status and the Influence of Parameters

Electrodeposition of some alloys and multilayer which exhibits the giant magneto resistance (GMR) effect, have been the subject of numerous studies. They have great potential for technological applications, such as magneto resistive sensors and magnetic recording devices. GMR effect is more usually seen in multilayer and alloys structure, when two magnetic layers are closely separated by a thin non-magnetic spacer layer. This paper deals with the review of literature available on electrodeposition of alloys and multilayer for GMR application. The effect of thickness of magnetic, non-magnetic layers, number of bi-layers, electrolyte pH, electrolyte temperature, additives and annealing process on GMR properties will be discussed.

Microstructure, magnetic and transport properties of magnetoresistive Cu80Fe x Ni20−x (x = 5, 10 and 15 at.%) ribbons

Microstructure, magnetic and transport properties of magnetoresistive Cu80FexNi20−x (x = 5, 10 and 15 at.%) melt-spun ribbons were studied for the as-spun and annealed for 2 h at 400 to 600 °C samples. The microstructure was characterised by means of X-ray diffraction, transmission electron microscopy, energy filtered transmission electron microscopy and Mossbauer spectrometry (MS). Magnetic and transport measurements such as magnetization, zero field cooled/field cooled and giant magnetoresistance (GMR) measurements at 5 and 300 K were performed. The aim of this work is to study the influence of the microstructure of as-spun and annealed ribbons on magnetic and transport properties at 5 and 300 K. We have precisely determined the nature of precipitation of nanoparticles, the relative proportion and the magnetic properties of each phase in such a system using MS at both temperatures. We report the conclusive observation of the magnetic behaviour of each phase which was correlated to the structural data to explain the GMR properties that are observed. The influence of magnetic interactions between nanoparticles on magnetic and magnetoresistive properties of these ribbons was determined. We have clearly shown the existence and the nature of the magnetic interactions that reduce the GMR.

Giant Magnetoresistance in (Ni&lt;sub&gt;60&lt;/sub&gt;Co&lt;sub&gt;30&lt;/sub&gt;Fe&lt;sub&gt;10&lt;/sub&gt;/Cu) Trilayer Growth by Opposed Target Magnetron Sputtering

The giant magnetoresistance thin film of (Ni60Co30Fe10/Cu) trilayer were grown onto Si (100) substrate by dc-opposed target magnetron sputtering (dc-OTMS) technique. The growth parameters are: temperature of 100 0C, applied voltage of 600 volt, flow rate of Ar gas of 100 sccm, and growth pressure of 5.2 x10-1 Torr. The effects of Cu layer thickness and NiCoFe layer thickness on giant magnetoresistance (GMR) property of (Ni60Co30Fe10/Cu) trilayer were studied. We have found that the giant magnetoresistance (GMR) ratio of the sample was varied depend on the non-magnetic (Cu) layer thickness. The variation of Cu layer thickness presents an oscillatory behavior of GMR ratio. This oscillation reflects the exchange coupling oscillations between ferromagnetic and antiferromagnetic states, which are caused by an oscillation in the sign of the interlayer exchange coupling between ferromagnetic layers. The GMR ratio is change with increasing of NiCoFe layer thickness and presents GMR ratio of 70.0 % at tNiCoFe = 62.5 nm.

Giant magnetoresistance (GMR) and ferromagnetic properties of DC and pulse electrodeposited Cu–Co alloys

Cu–Co ferromagnetic alloys occurring as granular films and exhibiting giant magnetoresistance (GMR) property have been synthesized using both DC and pulse electrodeposition techniques. The growth process of these electrodeposits comprising multiple granules of disparate morphology, magnetic features exhibits critical dependence on electrodeposition conditions. Using ferromagnetic resonance and magnetic hysteresis data, we have attempted a correlation between evolution of these electrodeposits and their ferromagnetic properties with special emphasis on GMR property.

Correlation between structural and giant magnetoresistance properties of Fe–Ag nanogranular films

Fe x Ag1−x granular thin-films, with the atomic Fe concentration, x, ranging from 0 up to 0.5, were deposited by dc magnetron co-sputtering. The giant magnetoresistance (GMR) intensity is maximum at x I = 0.32, while the maximum of GMR efficiency, γ, i.e., the change of GMR intensity for a unit change of reduced squared magnetization, is observed at x γ = 0.26. Owing to the spin-dependent scattering features, the GMR intensity and γ depend on both the concentration and the arrangement of the magnetic material. Therefore, to explain the difference between x I and x γ and to understand how the structural properties affect the magnetoresistive behaviour, we performed magnetization, Mossbauer and X-ray diffraction measurements as a function of x. X-ray data indicate that the granular films exhibit three different regimes: for x 0.32, a Fe–Ag saturated solid solution is detected, containing bcc Fe clusters whose size is about 10 nm. Differently, for all the concentrations, magnetization data show the presence of Fe precipitates, whose size increases with x, and the Mossbauer investigation confirms this picture. We find that the samples grown at x = x γ display the finest Fe dispersion within the Ag matrix, as the Fe–Ag solid solution is nearly at saturation and the Fe cluster size is of the order of a few nanometers; this arrangement possibly maximizes the magnetic/non-magnetic interface extension thus enhancing the GMR efficiency. If x is slightly increased, the increase in total Fe content compensates the GMR efficiency reduction, so the GMR intensity maximum is observed.

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 ribbons

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 (at. %) melt-spun and annealed ribbons was studied. The microstructure was characterized by means of energy filtered transmission electron microscopy, small angle neutron scattering and atom probe tomography. Giant magnetoresistance (GMR) measurements were made at low temperature. The samples were annealed for 2 h at different temperatures from 400 °C to 600 °C in order to modify their microstructure and thus their GMR properties. The magnetic behavior was correlated to the structural data to explain the GMR properties that are observed. A precise structural characterization, using atom probe tomography, small angle neutron scattering and energy filtered transmission electron microscopy, is presented. It reveals that no precipitates or clusters are present into the core grains of the as spun state; thus the sample is a solid solution. The magnetic properties measurements indicate that the ribbon exhibits a superparamagnetic behavior and presents relatively high GMR properties. These results imply that GMR can be obtained from a solid solution. Therefore, interface scattering is not the only precursor for GMR. The presence of diluted magnetic atoms leads to the formation of magnetic clusters that behave like superparamagnetic particles which are interacting and creating GMR.