Magnetoresistance Ratio Research Articles

Omnidirectionally Stretchable Spin-Valve Sensor Array with Stable Giant Magnetoresistance Performance.

Flexible magnetic sensors, which have advantages such as deformability, vector field sensing, and noncontact detection, are an important branch of flexible electronics and have significant applications in fields such as magnetosensitive electronic skin. Human skin surfaces have complicated deformations, which pose a demand for magnetic sensors that can withstand omnidirectional strain while maintaining stable performance. However, existing flexible magnetic sensor arrays can only withstand stretching along specific directions and are prone to failure under complicated deformations. Here, we demonstrate an omnidirectionally stretchable spin-valve sensor array with high stretchability and excellent performance. By integrating the modulus-distributed structure with liquid metal, the sensor can maintain its performance under complex deformations, enabling the overall system with omnidirectional stretchability. The fabricated spin-valve sensor exhibits a nearly unchanged giant magnetoresistance ratio of 8% and a maximum sensitivity of 0.93%/Oe upon omnidirectional strain up to 86% and can maintain stable performance without fatigue for over 1000 stretching cycles. Furthermore, this spin-valve sensor array is characterized by stable sensing performance for magnetic fields under complicated deformations and can be applied as a magnetosensitive electronic skin. Our results provide insights into the development of next-generation stretchable and wearable magnetoelectronics.

Spin transfer torque switching in double magnetic tunnel junctions based on dual MgO layers

We report fabrication and characterization of double magnetic tunnel junction (DMTJ) magneto-resistive random access memory cells that exhibit characteristic about 2X reduction of switching current compared to single reference layer junctions, but maintain high tunneling magnetoresistance ratio exceeding 120 %, high coercive fields of the free layer of more than 2 kOe for 65 nm cells, and magnetically stable reference layers with pinning fields above 6 kOe. Switching analysis performed for two different relative magnetization orientations of the reference layers shows that the net switching current is the result of combined spin transfer torque effects of the individual reference layers, with tunneling and spin-valve-like contributions adding constructively. Our work shows that efficient reduction of switching current can be achieved in double magnetic tunnel junctions with dual MgO layers where one of the layers has significantly lower resistance-area product to enable high magnetoresistance ratio.

Alloying two-dimensional VSi2N4 to realize an ideal half-metal towards spintronic applications.

Modulating the electronic properties of VSi2N4 with high Curie temperature to realize an ideal half-metal is appealing towards spintronic applications. Here, by using first-principles calculations, we propose alloying the VSi2N4 monolayer via substitutive doping of transition metal atoms (Sc-Ni, Y-Mo) at the V site. We find that the transition metal atom (except the Ni atom) doped VSi2N4 systems have dynamical and thermal stability. The doping of transition metal atoms can modulate the electronic structure of VSi2N4. Especially, the doping of the Sc/Y atom transforms VSi2N4 into an ideal half-metal, while the doping of the Ti/Zr atom leads to a half-semiconductor. For the half-metallic Sc- and Y-doped VSi2N4 devices, the magnetoresistance ratios up to 1010% and 108% are achieved, respectively. When the magnetization direction is parallel, the spin filtering efficiency of both devices reaches up to 100% at a low bias voltage, independent of the bias direction. When the magnetization direction is antiparallel, both show a dual spin filtering effect. Our findings offer a theoretical reference for modulating the electronic properties of two-dimensional materials towards spintronic applications.

Reconfigurable diode effect and giant tunnel magnetoresistance ratio in magnetic tunnel junctions based on spin gapless semiconductor and half metallic Heusler alloy

Reconfigurable diode effect and giant tunnel magnetoresistance ratio in magnetic tunnel junctions based on spin gapless semiconductor and half metallic Heusler alloy

Enhanced giant magnetoresistance in Heusler alloy (Co2FeSi/Ag)N multilayers for read sensor applications

Abstract We theoretically investigate the spin transport behavior of multilayer [ Co 2 FeSi / Ag ] N structure for the application of next-generation read sensors in hard disk drive. To demonstrate the potential of the Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device, we employ an atomistic model coupled with a spin accumulation model including the effect of a diffuse interface. The dynamics of magnetization is observed in the atomistic model and the calculation of magnetoresistance (MR) and MR ratio of the magnetic structure can be achieved by the spin accumulation model enabling us to investigate the spin transport behavior within the structure. The MR value can be directly calculated from the gradient of spin accumulation and spin current. The effect of injected current density is first investigated. It is found that increasing the current density results in a high MR ratio. Subsequently, to achieve a high performance reader, the number of coupled layers (N) is varied up to 16 to study its effect on the MR ratio. The calculated results indicate that increasing the number of layers N gives rise to the enhancement of the resistance change and MR ratio. At the critical point N = 5, further increasing N does not affect the MR ratio, which remains relatively unchanged. Interestingly, the MR ratio is doubled for N > 5 compared to N = 1. Our results demonstrate the possibility of enhancing the performance of multilayer CPP-GMR devices.

Unraveling the Interplay Between Memristive and Magnetoresistive Behaviors in LaCoO3/SrTiO3 Superlattice‐Based Neural Synaptic Devices

AbstractMemristors and magnetic tunnel junctions are showing great potential in data storage and computing applications. A magnetoelectrically coupled memristor utilizing electron spin and electric field‐induced ion migration can facilitate their operation, uncover new phenomena, and expand applications. In this study, devices consisting of Pt/(LaCoO3/SrTiO3)n/LaCoO3/Nb:SrTiO3 (Pt/(LCO/STO)n/LCO/NSTO) are engineered using pulsed laser deposition to form the LCO/STO superlattice layer, with Pt and NSTO serving as the top and bottom electrodes, respectively. The results show that both memristive and magnetoresistive properties can coexist without any compromise in performance, and the values of ROFF/RON and tunnel magnetoresistance (TMR) ratio are both improved by ≈1000% compared to a single‐period heterostructure. Notably, the Pt/(LCO/STO)5/LCO/NSTO device demonstrates superior multilevel storage performance, characterized by extended endurance, reliable retention, high ROFF/RON ratio, significant TMR ratio, and fundamental synaptic behaviors. Furthermore, density functional theory (DFT) is employed to calculate the changes in oxygen vacancies, affecting the overall energy bands and magnetic moments in the monolayer and multi‐periodic structures. Simulations using the handwritten digit recognition classification achieve the highest accuracy of 94.38%. These attributes suggest that the devices hold considerable promise for application in data storage and neuromorphic computing, offering a platform for high‐density neural circuits in intelligent electronic devices.

Full voltage control of giant magnetoresistance

The aim of voltage control of magnetism is to reduce the power consumption of spintronic devices. For a spin valve, the relative magnetic orientation for the two ferromagnetic layers is a key factor determining the giant magnetoresistance (GMR) ratio. However, achieving full voltage manipulation of the magnetization directions between parallel and antiparallel states is a significant challenge. Here, we demonstrate that by utilizing two exchange-biased Co/IrMn bilayers with opposite pinning directions and with ferromagnetic interlayer coupling between the two Co layers, the magnetization alignment of the two Co layers of a spin valve can be switched between antiparallel and nearly parallel states by voltage-induced strain, leading to a full voltage control of GMR in a repeatable manner. The magnetization rotating processes for the two Co layers under different voltages can be clearly demonstrated by simulations based on the Landau–Lifshitz–Gilbert equation. This work provides valuable references for the development of full voltage-controlled spintronic devices with low energy consumption.

Tunneling magnetoresistance and spin-orbit torque magnetization switching in ferrimagnetic Gd-Fe-Co based magnetic tunnel junction

Abstract Spin-orbit torque magnetization switching is studied in three terminal magnetic tunnel junctions with a ferrimagnetic Gd-Fe-Co free layer. Pt is used as a spin current generation layer and a Co-Fe-B synthetic antiferromagnet is used as the reference layer. A thin Fe-B layer is inserted between the Gd-Fe-Co free layer and the MgO barrier. The thickness of the Fe-B layer is varied from 4 to 12 Å. We find the tunnel magnetoresistance ratio increases with increasing Fe-B layer thickness until it saturates at ~14%, while the current density needed to reverse the magnetization of the Gd-Fe-Co/Fe-B layer via spin-orbit torque remains almost unchanged. The results highlight the effectiveness of the thin Fe-B layer to obtain sizable tunneling magnetoresistance and efficient spin-orbit-torque switching.

First principles electron transport in magnetoelectric SrRuO3/BaTiO3/SrTiO3/SrRuO3interfaces.

Recently, all-oxide ferroelectric tunnel junctions, with single or composite potential barriers based on SrRuO3/BaTiO3/SrTiO3(SRO/BTO/STO) perovskites, have drawn a particular interest for high density low power applications, due to their highly tunable transport properties and device scaling down possibility to atomic size. Here, using first principles calculations and the NEGFs formalism, we explore the electronic structure and tunneling transport properties in magnetoelectric SRO/BTO/mSTO/SRO interfaces, (m= 0, 2, or 4 unit cells), considering both the RuO6octahedra tilts and magnetic SRO electrodes. Our main results may be summarized as follows: i) The band alignment schemes predict that polarization direction may determine both Schottky barrier or Ohmic contacts form(STO)=0, but only Schottky contacts form(STO)=2 and 4 junctions; ii) The tunnel electroresistance and tunnel magnetoresistance ratios are evaluated at 0 and 300 K; iii) The most magnetoelectric responsive interfaces are obtained for them(STO)=2 heterostructure, this system also showing co-existent giant tunnel electroresistance and tunnel magnetoresistance effects; iv) The interfacial magnetoelectric coupling is not strong enough to control the tunnel magnetoresistance by polarization switching, in spite of significant SRO ferromagnetism.

Impact of Co doping on the magnetic and transport properties of FeRh

FeRh undergoes a first-order phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) state at ∼370 K, which is highly sensitive to strain and compositional changes. In this study, we investigate the magnetic and electronic properties of Co-doped FeRh films fabricated using a co-sputtering technique, to address how the magnetic transition behavior is influenced by the doping in FeRh films. By adjusting Co sputtering gun currents (=0, 5, 8, and 10 mA), we achieve Co doping levels from 1 to 2 at. %, where initial Co atoms (for 5 and 8 mA) substitute Rh sites, while doped Co levels (for 10 mA) begin to occupy Fe sites with unchanged Co doping level of 2 at. %. We find that Co substitution significantly lowers the transition temperature, attributed to an enhancement of the FM phase due to the contribution of magnetic Co doping. Furthermore, the Co doping leads to a remarkable increment in the magnetoresistance ratio during the transition, reaching up to 190% for only 2 at. % Co doping, while keeping the magnetization change. The Hall effect measurements indicate a slight reduction in carrier density with Co doping, maintaining changes in carrier type across the phase transition. These results highlight the tunable magnetic phase transition and resistance changes in Co-doped FeRh films. This study provides valuable insights into the complex physics underlying the Co doping in FeRh films, emphasizing their scientific value in understanding the mechanism of the AFM–FM transitions in achieving high magnetoresistance.

Analysis of the effect of the Fermi surface matching at Co–Fe and Cu interface on giant magnetoresistance effect using a combinatorial technique

Interfacial electronic band-matching (EBM) plays a crucial role in determining the spin-dependent transport properties and performance of spintronic devices. The final goal of this study is to establish a method to search for new material combinations that exhibit favorable EBM at the interfaces to achieve a superior performance in various spintronic devices using the machine learning technique combined with the first-principles calculations. As a first step, we investigate the effect of interfacial EBM on magnetoresistance (MR) by fabricating the current-in-plane giant magnetoresistive devices with compositionally graded Co1−βFeβ layers and Cu spacer. The MR ratio varies significantly across β = 0.11–1.0, with the highest MR of 17.5% observed at β ≈ 0.46, followed by a sharp decrease beyond β = 0.6. To analyze the β dependence of MR in terms of EBM with low computational cost, we calculate the simple Fermi surfaces of bcc Co1−βFeβ and Cu and evaluate the wave number (k) distance between their Fermi surfaces. The closest (furthest) Fermi surface match occurs at β ≈ 0.4 (1.0), which tends to be in good agreement with the observed MR trend. This suggests that a simple Fermi surface similarity analysis, when integrated with a machine learning technique, can be an effective method for efficiently identifying new material combinations with high EBM.

Spin photo detector by using a CoFeB magnetic tunnel junction

Abstract Ultra-fast photoelectric conversion devices are a crucial element in photonics applications and are the subject of intense research and development. In conventional high-speed photo detectors, photoelectric charge generation in semiconductors is rooted in a mechanism that directly outputs current. Owing to the dilemma of the amount of generated charge and high-speed output, it is being faced with fundamental difficult to achieve a higher response. Spin order, rather than charge generation, also exists as a phenomenon that enables ultrafast photoresponses, and magnetic tunnel junction (MTJ) are well-known high-speed electrical detection elements for magnetic states. In this study, we experimentally confirmed the magnetic switching of photoresponsive MTJ using a practical single CoFeB free layer with a high MR ratio of 80% by irradiation with laser light. Furthermore, we experimentally confirmed the operation of the reversible photo detector, and its rise time reached an ultrafast speed of 20 ps. We named it spin photo detector and it has huge potential applications that require ultrafast photo detection.

Achieving Significant Multilevel Modulation in Superior-quality Organic Spin Valve.

Organic semiconductors, characterized by their exceptionally long spin relaxation times (≈ms) and unique spinterface effects, are considered game-changers in spintronics. However, achieving high-performance and wide-range tunable magnetoresistance (MR) in organic spintronic devices remains challenging, severely limiting the development of organic spintronics. This work combines straintronic multiferroic heterostructures with organic spin valve (OSV) to develop a three-terminal OSV device with a gate structure. The device exhibits a record-high MR ratio of 281% which 10 times higher than the average in polymer systems. More importantly, this work can perform multilevel writing operations on the device using gate voltages and create at least 10 stable spin-dependent working states within a single device. Both experiments and theoretical calculations confirm such an extraordinary tunability range originates from the synergistic effects of strain and charge accumulation that amplified by the spinterface. This study demonstrates the potential of OSV systems for efficient spin manipulation and highlights the spinterface as an ideal platform for amplifying spin effects for next-generation spintronic devices.

Double-barrier magnetic tunnel junctions with enhanced tunnel magnetoresistance

Tunnel magnetoresistance (TMR) ratio is a key parameter characterizing the performance of a magnetic tunnel junction (MTJ), and a large TMR ratio is essential for the practical application of it. Generally, the traditional solutions to increasing the TMR ratio are to choose different material combinations as the ferromagnetic (FM) leads and nonmagnetic tunnel barrier. In this work, we study an architecture of MTJs of “FM/barrier/FM/barrier/FM” with double barriers, in contrast to the traditional single barrier structure “FM/barrier/FM.” We first analytically show that double barrier MTJ will generally have much higher TMR ratio than the single barrier MTJ and then substantiate it with the well-known example of “Fe/MgO/Fe” MTJ. Based on density functional calculations combined with nonequilibrium Green's function technique for quantum transport study, in the single barrier “Fe/MgO/Fe” MTJ, the TMR ratio is obtained as 122%, while in the double barrier “Fe/MgO/Fe/MgO/Fe” MTJ, it is greatly increased to 802%, suggesting that double barrier design can greatly enhance the TMR and can be taken into consideration in the design of MTJs.

High Electrical Conductance in Magnetic Emission Junction of Fe3GeTe2/ZnO/Ni Heterostructure via Selective Spin Emission through ZnO Ohmic Barrier.

The insulator is essential for magnetic tunneling junction (MTJ) that increases magnetoresistance (MR) by decoupling magnetization directions between two ferromagnets. However, wide bandgap tunnel barrier blocks the thermionic emission of electrons, significantly reducing electrical conductance through MTJ. Here, a magnetic emission junction (MEJ) is demonstrated for the first time using an Fe3GeTe2 (FGT)/ZnO/Ni heterostructure with very high electrical conductance. The conduction band of ZnO (electron affinity 4.6eV) aligns with Fermi levels (EF) of FGT (4.47eV) and Ni (4.58eV) ferromagnets and forms an Ohmic barrier, enabling free spin-electron emission through ZnO barrier and high electrical conductance. In contrast to the typical positive MR in MTJ by majority spin tunneling, negative MR is observed in FGT/ZnO/Ni MEJ. The minority spin electrons of Ni, with maximum states near the EF, are dominantly emitted to FGT over the ZnO barrier, while majority spin electrons of Ni, with maximum states below the EF, are blocked by it. In the FGT/FGT/ZnO/Ni heterostructure, the MR ratio is further increased by combining positive and negative MR at the MTJ (FGT/FGT) and MEJ (FGT/ZnO/Ni), respectively. As a result, FGT-MEJ exhibits 10-1000 orders higher conductance than other 2D-MTJs, while MR ratio remains similar to other 2D-MTJs.

Field‐Free Perpendicular Magnetic Memory Driven by Out‐of‐Plane Spin‐Orbit Torques

AbstractMagnetic memory based on spin‐orbit torque (SOT) is a promising candidate for the next‐generation storage devices. Materials that generate out‐of‐plane spin polarization (σz) are highly desired and actively pursued as the SOT generator, due to its ability to achieve field‐free SOT switching of perpendicular magnetization. However, integrating σz into perpendicular magnetic tunnel junction for efficient data writing is not realized. Here, utilizing σz from antiferromagnetic spin Hall effect in Mn2Au, σz‐enabled field‐free SOT switching of perpendicular magnetic tunnel junctions is realized demonstrating a magnetic memory with both writing and reading electrically. The tunnel magnetoresistance ratio achieves 66% with a critical current density of 5.6 × 106 A cm−2 at room temperature. Such field‐free fully SOT switching is further directly confirmed by domain imaging via magneto‐optical Kerr effect microscopy. In addition to enabling field‐free switching, σz is proposed to assist ultrafast and more efficient switching of perpendicular magnetization compared with conventional in‐planes ones, based on simulations. This research advances the application of out‐of‐plane SOTs and paves the way for high‐density, high‐speed, and low‐power magnetic memory.

First principle atomistic modelling of magnetic tunnel junction (MTJ) to enhance its tunnel magneto-resistance (TMR) ratio

Abstract This paper investigates the impact of electrode materials on the Tunnel Magneto-Resistance (TMR) ratio of Magnetic Tunnel Junction (MTJ) device. Four different structures of MTJ have been simulated by using cobalt (Co), Nickel (Ni), Iron (Fe) and two alloy materials of nickel-iron (NiFe) and cobalt-iron (CoFe). These materials have been used as ferromagnetic electrodes. Mulliken population and transmission spectrum observed in both parallel and antiparallel configurations of these devices to understand the spin transport properties and Tunnel Magneto-Resistance (TMR) ratio has been estimated. The first principal study was performed based on density function theory (DFT) and Non-equilibrium Green’s Function (NEGF) computational methods using the QuantumATK simulation tool to study properties such as band structure, the density of states (DOS), Spin Transfer Torque (STT), I-V characteristics and TMR. This study explores how different electrode materials affect the Tunnel Magneto-Resistance (TMR) ratio in Magnetic Tunnel Junction (MTJ) devices. With these results, it is observed that cobalt-based MTJ devices (that is Co-MgO-Fe and CoFe-MgO-CoFe) exhibit higher TMR ratio as compared to Nickel- and Iron-based MTJ devices (that is NiFe-MgO-NiFe and Ni-MgO-Fe). As Cobalt has a high spin polarization this property makes it suitable for use in spintronics devices like MTJs, where the manipulation of electron spins is essential for data storage and information processing. These findings can be employed to improve the performance characteristics of the MTJ-based Random Access Memory (MRAM) in the field of spintronics.

Large magnetoresistance and high spin-transfer torque efficiency of Co2MnxFe1−xGe (0 ≤ x ≤ 1) Heusler alloy thin films obtained by high-throughput compositional optimization using combinatorially sputtered composition-gradient film

Half-metallic ferromagnetic Heusler alloys having high spin polarization are promising candidates to realize large magnetoresistance (MR) ratio and high spin-transfer torque (STT) efficiency in next-generation spintronic devices. Since the Heusler alloy properties are sensitive to composition, optimizing the composition is crucial for enhancing device performance. Here, we report the fabrication of high-performance current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices using Co2MnxFe1−xGe (0 ≤ x ≤ 1) Heusler alloy, employing a high-throughput and detailed composition optimization method. The method combined composition-gradient films and local measurements to enable the composition variation from Co2FeGe to Co2MnGe to be efficiently studied on a single library sample with a small composition interval. The CPP-GMR devices fabricated from stacks annealed at 250 °C showed a clear composition dependence of MR with the maximum of MR ratio ∼38% in the Mn-rich region of x = 0.85. By increasing the annealing temperature to 350 °C, the MR ratio increased to ∼45% along with high STT efficiency ∼0.6 in the broad composition range of 0.2 ≤ x ≤ 0.7. The optimal composition for the highest MR changed with annealing temperature because of the stability of the GMR stack being higher in the lower x range. The record high MR for the all-metal CPP-GMR devices, at low annealing temperature of 250 °C was achieved by the detailed composition optimization. These results present the high potential of Co2MnxFe1−xGe and provide a comprehensive guidance on the composition optimization for achieving large MR ratio and high STT efficiency in the CPP-GMR devices.

Magnetic proximity effect and spin transport properties of MnPc/CuPc/MnPc molecular spintronic device

Molecular-scale spintronic devices show great application potential in information storage due to tiny size and rich controllability. Spin transport of molecular devices relies heavily on the magnetic interaction between magnetic metal atom and molecule, which is the core of determining the performance of spintronic devices. In this study, the magnetic proximity effect in MnPc/CuPc/MnPc molecular device and the influence on spin transport were investigated using non-equilibrium Green’s function method in combination with density functional theory. Mn atoms in MnPc molecules not only endow magnetism with system, but also trigger magnetic proximity effect which works in synergy with the spin filtering of phthalocyanine molecules to achieve a spin injection efficiency of 100 % in molecular device, and this efficiency remains stable under bias voltage. The MnPc/CuPc/MnPc molecular device shows a tunneling magnetoresistance ratio of up to 4165 % at 5 mV, indicating potential application in multifunctional spintronic devices. This work elucidates the unique physical properties and excellent performance of MnPc/CuPc/MnPc molecular device, providing valuable insights for spintronic applications.

Temperature dependence of spin transport behavior in Heusler alloy CPP-GMR

In this study, we investigate the effect of temperature on the performance of a read sensor by utilizing an atomistic model coupled with a spin transport model. Specifically, we study the temperature dependence of spin transport behavior and MR outputs in a Co2FeAl0.5Si0.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {Co}_2\ ext {FeAl}_{0.5}\ ext {Si}_{0.5}$$\\end{document} (CFAS)(5nm)/Cu(5nm)/CFAS(5nm) trilayer with diffusive interfaces. Initially, the two-channel model of spin-dependent resistivity is used to calculate the temperature dependence of spin transport parameters which serves as essential input for the spin accumulation model. Our findings demonstrate that as the temperature increases, the spin transport parameters and magnetic properties decrease due to the influence of thermal fluctuation. At a critical temperature, where the ferromagnet transitions to a paramagnetic state, we observe zero spin polarization. Furthermore, at elevated temperatures, the spin accumulation deviates from the equilibrium value, leading to a reduction in the magnitude of spin current and spin transport parameters due to thermal effects. As a consequence, the MR ratio decreases from 65% to 20% with increasing temperature from 0 to 400 K. Our results are consistent with previous experimental measurements. This study allows to deeply understand the physical mechanism in the reader stack which can significantly benefit reader design.