Giant Magnetoresistance Ratio Research Articles

Theoretical characterization of the magnetoresistance in magnetic multilayers with antiferromagnetic coupling

Spin-valves (SVs) constitute a significant class of magnetic metal structures with a large range of technological applications. This class of structure offers interesting magnetic properties due to their alternation with the non-magnetic layers. The SVs fortunately have good magnetic properties at room temperature (RT). This study intends to use Boltzmann Approach–BA, to treat the magetotransport properties of Co-based SV. Outer-surface scattering effects on magnetoresistance (MR) performance encountered in these structures are investigated by varying the interfacial chemical composition. Analysis of the results reveals the existence of a significant improvement of magnetic phenomenon for a scattering that is more and more specular of the conduction electrons through outer-surface. A giant MR (GMR) of amplitude 136.9 % is obtained for an interfacial geometric roughness of magnitude 2 Å. The GMR ratio is the result of large asymmetry in the spin-dependent interfacial scattering and a completely specular outer-surface scattering.

High‐Throughput Optimization of Magnetoresistance Materials Based on Lock‐In Thermography

AbstractWith the giant magnetoresistance (GMR) effect serving as a vital component in modern spintronic technologies, researchers are dedicating significant efforts to improve the performance of GMR devices through material exploration and design optimization. However, traditional GMR measurement approaches are inefficient for comprehensive material and device optimization. This study proposes a high‐throughput current‐in‐plane GMR measurement technique based on thermal imaging of Joule heating utilizing lock‐in thermography (LIT). This LIT‐based technique is advantageous for efficiently evaluating films with varying compositions and thickness gradients, which is crucial for ongoing material exploration and design optimization to enhance the GMR ratio. First, it is demonstrated that using CoFe/Cu multilayers, the simple Joule heating measurement based on LIT enables quantitative estimation of the GMR ratio. Then, to confirm the usefulness of the proposed method in high‐throughput material screening, a case study is shown to investigate the GMR of CoCu‐based granular films with a composition gradient. These techniques allow to determine the optimum composition with maximum GMR ratio using the single composition‐gradient film and reveal Co22Cu78 as the optimal composition, yielding the largest GMR ratio among the reported polycrystalline CoCu‐based granular films. This demonstration accelerates the material and structural optimization of GMR devices.

Exchange coupling in (Co/Pt)2/Nb/(Pt/Co)2 multilayers induced by the Yu–Shiba–Rusinov bound states

The Ruderman–Kittel–Kasuya–Yosida (RKKY) theory of oscillatory exchange interaction in synthetic antiferromagnetic multilayers results in the oscillation behavior of giant magnetoresistance ratio. In addition, the formation of Yu–Shiba–Rusinov (YSR) bound states will induce an extra antiferromagnetic interaction, which is expected to mediate stronger exchange coupling than conventional RKKY interaction. However, the YSR bound states have only been studied in some superconducting hosts with magnetic impurities. The narrow range of material systems that are not compatible with the device integration architecture limits the practical application of YSR interaction. Here, we observe the RKKY interaction and provide the evidence for YSR interaction in Pt/(Co/Pt)2/Nb/(Pt/Co)2/Pt synthetic antiferromagnetic multilayers by quantitatively determining the coupling energy via ferromagnetic resonance technique.

Transport properties of Mn-doped/adsorbed zigzag boron nitride nanoribbon based nanodevices

We are conducting research into the spin transport characteristics of models that are built from zigzag Boron Nitride Nanoribbons (ZBNNRs) that have been doped and adsorbed with Mn. These investigations are made possible by using the non-equilibrium Green’s function (NEGF) formalism in conjunction with Density Functional Theory (DFT). We have scrutinized the electronic structures of six different models, and have chosen two for a deeper exploration of its’ transport characteristics. Our computational findings highlight an unusual occurrence where a Mn atom substitutes a B atom in ZBNNRs, resulting in ZB(Mn)NNRs that exhibit significant Giant Magnetoresistance (GMR) and Rectification ratio (RR) - peaking at 106 and 105 respectively, along with the presence of negative differential conductance (NDC) effects. The detected GMR, NDC, and rectification characteristics in ZB(Mn)NNRs offer an optimistic outlook for the conceptualization of future nanodevices.

Deterministic Magnetization Reversal in Synthetic Antiferromagnets using Natural Light.

Traditional current-driven spintronics is limited by localized heating issues and large energy consumption, restricting their data storage density and operation speed. Meanwhile, voltage-driven spintronics with much lower energy dissipation also suffers from charge-induced interfacial corrosion. Thereby finding a novel way of tuning ferromagnetism is crucial for spintronics with energy-saving and good reliability. Here, a visible light tuning of interfacial exchange interaction via photoelectron doping into synthetic antiferromagnetic heterostructure of CoFeB/Cu/CoFeB/PN Si substrate is demonstrated. Then, a complete, reversible magnetism switching between antiferromagnetic (AFM) and ferromagnetic (FM) states with visible light on and off is realized. Moreover, a visible light control of 180° deterministic magnetization switching with a tiny magnetic bias field is achieved. The magnetic optical Kerr effect results further reveal the magnetic domain switching pathway between AFM and FM domains. The first-principle calculations conclude that the photoelectrons fill in the unoccupied band and raise the Fermi energy, which increases the exchange interaction. Lastly, a prototype device with visible light control of two states switching with a 0.35% giant magnetoresistance ratio change (maximal 0.4%), paving the way toward fast, compact, and energy-efficient solar-driven memories is fabricated.

A strain-controlled magnetostrictive pseudo spin valve

Electric-field control of magnetism via an inverse magnetostrictive effect is an alternative path toward improving energy-efficient storage and sensing devices based on a giant magnetoresistance effect. In this Letter, we report on lateral electric-field driven strain-mediated modulation of magnetotransport properties in a Co/Cu/Py pseudo spin valve grown on a ferroelectric 0.7Pb[Mg1/3Nb2/3)]O3–0.3PbTiO3 substrate. We show a decrease in the giant magnetoresistance ratio of the pseudo spin valve with the increase in the electric field, which is attributed to the deviation of the Co layer magnetization from the initial direction due to strain-induced magnetoelastic anisotropy contribution. Additionally, we demonstrate that strain-induced magnetic anisotropy effectively shifts the switching field of the magnetostrictive Co layer, while keeping the switching field of the nearly zero-magnetostrictive Py layer unaffected due to its negligible magnetostriction. We argue that magnetostrictively optimized magnetic films in properly engineered multilayered structures can offer a path to enhancing the selective magnetic switching in spintronic devices.

Huge giant-magnetoresistance of Co/Ru/L11-CoPt multi-layer pseudo-spin valve

Co/Ru/L11-CoPt based thin film as pseudo spin valve prepared by DC magnetron sputtering deposition. The magnetic and magnetoresistance properties with the thickness change of L11-CoPt layer were investigated. The resulting spin valve exhibited well-different out-of-plane and in-plane hysteresis loops. The coercivities changed unpredictably at different thicknesses of L11-CoPt layer. A perpendicular giant magnetoresistance ratio is obtained about 59.70 % and 160 % with current-out-of-plane measurements for the pattern and cross-linking structures of Pt(20 nm)/Co(2.5 nm)/Ru(1.5 nm)/[L11-CoPt]8/Pt(20 nm)/glass substrate, respectively. It was ascribed this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Co free layer and L11-CoPt reference layer through Ru spacer layer, and considered as the ferromagnetic interlayer exchange coupling.

Observation of the giant magneto-Seebeck effect in a metastable Co50Fe50/Cu multilayer

We report the observation of the giant magneto-Seebeck (GMS) effect in an epitaxially grown Co50Fe50/Cu multilayer film with metastable bcc Cu spacers under an in-plane temperature gradient. The magnetization-dependent switching ratio of the Seebeck coefficient, GMS ratio, and switching ratio of the thermoelectric power factor reach approximately −50% and 280% at room temperature, respectively, which are higher than those previously reported in magnetic multilayers with the current-in-plane geometry. By measuring the temperature dependence of both GMS and giant magnetoresistance (GMR) effects, we found that the GMS ratio remains high at high temperatures, while the GMR ratio quickly decreases with increasing temperature, where the spin-dependent electron scattering dominantly affects the large GMS effect in the Co50Fe50/Cu multilayer.

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.

Multifunctional spintronic device based on zigzag SiC nanoribbon heterojunction via edge asymmetric dual-hydrogenation

The authors propose a method to obtain the multifunctional spintronic device by investigating the spin-resolved transport characteristics of zigzag SiC nanoribbon (zSiCNR) heterojunction via edge asymmetric dual-hydrogenation. The spin-resolved band structures show that the dual-hydrogenation on edge C or Si atoms all can change the initial metallicity of the pristine zSiCNR with the edge mono-hydrogenation to semiconductor in the presence of ferromagnetic field. The spin-resolved current-voltage characteristics of the zSiCNR heterojunction can show spin current rectification in the same rectify direction under the parallel magnetic field. The up-spin rectification ratio of our junction can be close to 10 13 at −0.5 V, which is much larger than rectification ratios of the previous junctions induced by the anti-parallel magnetic field. The zSiCNR heterojunction also exhibits a perfect spin filtering behavior with 100% spin filtering efficiency in both positive and negative bias regions under the anti-parallel magnetic field. More interestingly, the magnetoresistance is achieved by manipulating the external magnetic field in our zSiCNR heterojunction with the giant magnetoresistance ratio 5000% at 0.5 V. Therefore, the zSiCNR heterojunction via edge asymmetric dual-hydrogenation can be designed into the multifunctional spintronic devices, which has broad application prospects in the field of future spintronics. • Zigzag silicon carbon nanoribbon has potential in spin devices. • Giant spin current rectification is obtained in the presence of a ferromagnetic field. • Maximum spin current rectification ratios is closing to 10 13 . • Perfect spin filtering and magnetoresistance behaviors are also obtained.

Electronic structure, magnetoresistance and spin filtering in graphene|2 monolayer-CrI33|graphene van der Waals magnetic tunnel junctions.

In the pursuit of designing van der Waals magnetic tunneling junctions (vdW-MTJs) with two-dimensional (2D) intrinsic magnets, as well as to quantitatively reveal the microscopic nature governing the vertical tunneling pathways beyond the phenomenological descriptions on CrI3-based vdW-MTJs, we investigate the structural configuration, electronic structure and spin-polarized quantum transport of graphene|2 monolayer(2ML)-CrI3|graphene heterostructure with Ag(111) layers as the electrode, using density functional theory (DFT) and its combination of non-equilibrium Green's function (DFT-NEGF) methods. The in-plane lattice of CrI3 layers is found to be stretched when placed on the graphene (Gr) layer, and the layer-stacking does not show any site selectivity. The charge transfer between CrI3 and Gr layers make the CrI3 layer lightly electron-doped, and the Gr layer hole-doped. Excitingly, the inter-layer hybridization between graphene and CrI3 layers render the CrI3 layer metallic in the majority spin channel, giving rise to an insulator-to-half-metal transition. Due to the metallic/insulator characteristics of the spin-majority/minority channel of the 2ML-CrI3 barrier in vdW-MTJs, Gr|2ML-CrI3|Gr heterostructures exhibit an almost perfect spin filtering effect (SFE) near the zero bias in parallel magnetization, a giant tunneling magnetoresistance (TMR) ratio up to 2 × 104%, and remarkable negative differential resistance (NDR). Our results not only give an explanation for the observed giant TMR in CrI3-based MTJs but also show the direct implications of 2D magnets in vdW-heterostructures.

Tunable giant magnetoresistance ratio in bilayer CuPc molecular devices.

We investigate the influence of the distance between the buffer layer and the central molecule on the electrical transport, spin-filter transport, magnetoresistance effects and thermoelectric properties of a bilayer CuPc molecular device with V-shaped zigzag-edged graphene nanoribbon (VZGNR) electrodes by combining density functional theory and the non-equilibrium Green's function. The results show that the spin-dependent total conductance and spin filter efficiency of the bilayer CuPc molecular device reach a maximum with a parallel spin configuration (PC) when the carbon atom at the edge of the electrode is in the center of the carbon atom at the edge of the bilayer molecules due to the stronger coupling interaction between the double-layer molecules and the leads. Moreover, the spin polarization of the bilayer CuPc molecular device is reversed at certain distances; there is a minimum spin filter efficiency (SFE) of −99.93448% and a maximum SFE of 97.91% observed in the anti-parallel spin configuration (APC) of the device and there is a minimum SFE of −26.03175% and a maximum SFE of 99.99996% observed with the PC at zero bias. The SFE oscillates with increasing considered bias voltage in the PC and APC when the distances are d = 0 Å and d = −1.06 Å, and a negative differential resistance (NDR) effect was observed. For the PC and APC, there is a giant magnetoresistance (MR) effect and the MR ratio exceeds 5.21 × 107% (99.9996%), and the MR ratio oscillates with increasing considered bias voltage when d = 0 Å. The MR ratio could be reserved by applying a certain bias voltage. These transport behaviors can be well understood by analyzing the transmission spectra, projected density of states and scattering states. There are pure spin Seebeck coefficients and pure charge Seebeck coefficients at certain temperatures when the distances are certain values, which means that the corresponding temperature differences could produce pure spin current and pure charge current, respectively. Our results provide new ideas for designing ultrahigh-performance spintronic molecular devices.

Magnetic and electronic properties of metallic multilayers: monolayer thickness effects

Giant magnetoresistance (GMR) is discussed at RT for the Co(111)/Cu(111) metallic bilayer system. The theoretical approach based on the original model developed by Hood Falicov and Penn has been used and extended in this analysis. We study the effect of the Cu and Co monolayer thickness on the behavior and amplitude of GMR. An identical decreasing behavior in the evolution of GMR is observed by varying the thickness of each monolayer. The resistivitiy of a ferromagnetic configuration (up-up, $$^{{\uparrow \uparrow }})$$ behaves differently. The influence of phenomenological scattering on the variation of GMR as a function of the interlayer thickness is also taken into account. We analyze experimental data giving the bilayer number dependence on the GMR ratio of Co/Cu multilayers at RT.

Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions

Giant tunnel magnetoresistance (TMR) ratios of 417% at room temperature (RT) and 914% at 3 K were demonstrated in epitaxial Fe/MgO/Fe(001) exchange-biased spin-valve magnetic tunnel junctions (MTJs) by tuning growth conditions for each layer, combining sputter deposition for the Fe layers, electron-beam evaporation of the MgO barrier, and barrier interface tuning. Clear TMR oscillation as a function of the MgO thickness with a large peak-to-valley difference of ∼80% was observed when the layers were grown on a highly (001)-oriented Cr buffer layer. Specific features of the observed MTJs are symmetric differential conductance (dI/dV) spectra for the bias polarity and plateau-like deep local minima in dI/dV (parallel configuration) at |V| = 0.2–0.5 V. At 3 K, fine structures with two dips emerge in the plateau-like dI/dV, reflecting highly coherent tunneling through the Fe/MgO/Fe. We also observed a 496% TMR ratio at RT by a 2.24 nm-thick-CoFe insertion at the bottom-Fe/MgO interface.

Spin-resolved transport properties of atomic carbon chain between sawtooth zigzag-edge graphene nanoribbons electrodes

ABSTRACT We investigate the magnetic transport properties for a molecular device model constructed by a carbon atomic chain embedding in two hydrogen-passivated graphene nanoribbons (GNRs) electrodes with sawtooth zigzag edges. The spin-dependent transport simulation is carried out by the first-principles approach based on the density functional theory combing with nonequilibrium Green's function formalism. It is found that the dual spin-filtering effect with the perfect efficiency up to 100, high-performance dual-spin diode effect with the rectification ratio reaches about and obvious negative differential resistance behaviour with a peak-to-valley ratio near are numerically observed in such proposed molecular device. Particularly, a giant magnetoresistance ratio approaching is also observed, which is two orders magnitude higher than the value of a zigzag-edge GNR. These findings suggest that our proposed device has multifunction with highly effective spin-filter, spin-diode, spin-valve performance.

Quenching of an antiferromagnet into high resistivity states using electrical or ultrashort optical pulses

Ultra-fast dynamics, insensitivity to external magnetic fields, or absence of magnetic stray fields are examples of properties that make antiferromagnets of potential use in the development of spintronic devices. Similar to their ferromagnetic counterparts, antiferromagnets can store information in the orientations of the collective magnetic order vector. However, also in analogy to ferromagnets, the readout magnetoresistivity signals in simple antiferromagnetic films have been weak and the extension of the electrical reorientation mechanism to optics has not been achieved. Here we report reversible and reproducible quenching of an antiferromagnetic CuMnAs film by either electrical or ultrashort optical pulses into nano-fragmented domain states. The resulting resistivity changes approach 20\% at room temperature, which is comparable to the giant magnetoresistance ratios in ferromagnetic multilayers. We also obtain a signal readout by optical reflectivity. The analog time-dependent switching and relaxation characteristics of our devices can mimic functionality of spiking neural network components.

Effective Co-rich ternary CoFeNi alloys for spintronics application

The dependence of crystal structure, hysteresis properties and magnetoresistance on composition of ternary CoFeNi alloy has been studied for glass/Ta/(Ni80Fe20)60Cr40/[CoFeNi/Cu(2.2 nm)]n/Ta multilayers. Two series of Co-rich CoFeNi alloys were used. In series (I) the Co content decreases from 90 to 67 at. %, Fe content increases from 10 to 20 at.% and Ni content – from 0 to 13 at.%. Series (II) includes alloys with a fixed Co content: Co70Fe30-xNix (x = 5, 10, 15 and 20). For each type of ternary alloys the multilayer composition was optimized in order to obtain maximum giant magnetoresistance (GMR). The highest GMR ratios of 30–33% at room temperature are revealed in multilayers of series (I) alloys. It has been established that the most effective CoFeNi alloys, using which the GMR multilayers have a high GMR ratio in combination with low coercivity, are located in a narrow region of the ternary diagram near the Co70Fe20Ni10 composition. A deviation of the ternary alloy composition from this optimal one leads either to a decrease in the GMR ratio, or to a significant increase of coercivity.

Giant thermal magnetoresistance driven by graphene magnetoplasmon

In this work, we have predicted a giant thermal magnetoresistance for the thermal photon transport based on the tunable magnetoplasmon of graphene. By applying an external magnetic field, we find that the heat flux can be modulated by approximately three orders of magnitude. Accordingly, both negative and giant relative thermal magnetoresistance ratios are achieved for magnetic fields with a maximum strength of 4 Tesla. This effect is mainly caused by the suppression and enhancement of scattering interactions mediated by a graphene magnetoplasmon. Specifically, it has never been achieved before for nanoparticles, which have no response to magnetic fields. The effect is remarkable at these reasonable strengths of fields and, thus, has considerable significance for real-life applications. It is also expected to enable technological advances for thermal measurement-based magnetic sensors and magnetically thermal management.

Room temperature high Giant Magnetoresistance graphene based spin valve and its application for realization of logic gates

In this study we carried out first principle calculations for spin dependent electronic transport in our proposed spintronic device consisting of graphene nanoribbon as scattering region with cobalt electrodes and magnesium oxide as tunneling barrier. The I–V Characteristics are calculated by using Non-Equilibrium Green's Function formalism in combination with Semi-Empirical (SE) Extended Huckel Theory (EHT) using Atomistic Tool Kit software at room temperature. The high value of GMR (Giant Magnetoresistance) is recommended for spintronic devices. The results reveal that the device shows a very high GMR ratio of 5.16×104%. The device also shows very low off state current, therefore negligible off state power consumption. The investigation of spin dependent non equilibrium transport is done by examining bias dependent transmission coefficients. Furthermore, some basic logic gates, like NOT, AND and NOR have been realized from the modeled device. The device may also find applications in data storage, magnetic field sensors etc.

Giant magnetoresistance ratio in a current-perpendicular-to-plane spin valve based on an inverse Heusler alloy Ti2NiAl.

A Ti2NiAl inverse Heusler alloy based current-perpendicular-to-plane (CPP) spin valve (SV) with various kinds of atomic terminated interfaces has been designed to explore the potential application of Heusler alloys in spintronics devices. By performing first principles calculations combined with the nonequilibrium Green’s function, it is revealed that spin magnetic moments of interfacial atoms suffer a decrease, and the electronic structure shows that the TiNiB-terminated structure possesses the largest interface spin polarization of ≈55%. Our study on spin-transport properties indicates that the total transmission coefficient at the Fermi level mainly comes from the contribution from the spin up electrons, which are regarded as the majority of the spin electrons. When the two electrodes of the CPP-SV device are in parallel magnetization configuration, the interface containing Ti and Ni atoms possesses a higher spin up transmission coefficient than the interface containing Ti and Al atoms. The device with the TiNiB-terminated interface possesses the largest magnetoresistance ratio of 3.28 × 105, and it has great application potential in spintronics devices.