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Replacing the ferromagnet with ferrimagnet (FiM) in the magnetic tunnel junction (MTJ) allows faster magnetization switching in picoseconds. The operation of a memory cell that consists of the MTJ and a transistor requires reversable magnetization switching. When a constant voltage is applied, we find that the spin-transfer torque can only switch the FiM-MTJ from parallel to antiparallel state. This stems from the small switching window of FiM and the dynamic resistance variation during the magnetization switching. We find the resulting current variation can be suppressed by reducing the magnetoresistance ratio. Furthermore, we demonstrate that the switching window can be expanded by adjusting the amount of Gd in FiM. We predict that the polarity of both switching current (J c,switch) and oscillation current (J c,osc) reverses at the angular momentum compensation point but not the magnetization compensation point. This anomalous dynamic behavior is attributed to the different physical nature of magnetization switching and oscillation in FiM, which must be considered when designing FiM-based MRAM. [ABSTRACT FROM AUTHOR]

• FeMn electrodes were used to create molecular spintronics devices with MTJs as test beds. • SMM molecules showed different responses near room temp and below Neel temp on 10,000 MTJs. • KPAFM revealed changes in surface potential after spin channels were established in MTJs. • MTJMSD enabled integration of molecular channels with various stable metal electrodes. The integration of single-molecule magnets (SMMs) into magnetic tunnel junctions (MTJs) offers significant potential for advancing molecular spintronics, particularly for next-generation memory devices, quantum computing, and energy storage technologies such as solar cells. In this study, we present the first demonstration of SMM-induced spin-dependent properties in an antiferromagnet-based MTJ molecular spintronic device (MTJMSD). We engineered cross-junction-shaped devices comprising FeMn/AlO x /NiFe MTJs. The AlO x barrier thickness where the exposed junction edges meet was comparable to the SMM length, facilitating the incorporation of SMM molecules as spin channels for spin-dependent transport. The SMM channels enabled long-range magnetic moment ordering around molecular junctions, which were precisely engineered via fabrication processes. The SMM, composed of a [Mn 6 (μ 3 -O) 2 (H 2 N-sao) 6 (6-atha) 2 (EtOH) 6 ] (H 2 N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate) complex, featured thioester groups at the ends that upon hydrolysis they form bonds with the magnetic electrodes. SMM-treated junctions demonstrated a significant current enhancement, reaching up to 7 μA at an input voltage of 60 mV. Furthermore, SMM-doped junctions exhibited current stabilization in the μA range at lower temperatures, whereas the bare electrodes showed current suppression to the picoampere range. Magnetization measurements conducted at 55 K and 300 K on pillar-shaped devices revealed a reduction in magnetic moment at low temperatures. Additionally, Kelvin probe atomic force microscopy (KPAFM) measurements confirmed that SMM integration transformed the electronic properties over long ranges.These findings are attributed to the spin channels formed between magnetic metal electrodes, which enhance spin polarization at each magnetic electrode. Our research highlights the potential of using antiferromagnetic materials, characterized by minimal stray fields and zero net magnetization, to transform MTJMSD devices. [ABSTRACT FROM AUTHOR]

• Discovery of new half-metal nanoribbons. • The spintronic devices exhibit a perfect spin-filtering phenomenon. • The spintronic devices exhibit extremely high TMR. Since the successful synthesis of α-phosphorus carbide (α-CP) using carbon doping technology, α-CP has exhibited excellent carrier mobility and anisotropy at room temperature, underscoring its potential for spintronic applications. The application of CP in spintronic devices is limited due to its lack of magnetism. Effective magnetic injection in non-magnetic semiconductors can typically be achieved by doping with magnetic atoms. In this study, we calculated the electromagnetic properties of transition metal (TM) atoms adsorbed at different positions on α-CP using first principles. Notably, we found that α-CP nanoribbons adsorbed with Fe and Mn atoms of a specific width exhibit stable half-metallicity. We discovered that α-CP nanoribbons adsorbed with Fe and Mn atoms of a specific width exhibit stable half-metal properties and design magnetic tunnel junctions with half-metallic Fe_H12 and Mn_H12 adsorption structures. The results show that Mn_H12 and Fe_H12 devices exhibit a highly efficient spin filtering effect, with a TMR as high as 5521%. These findings provide theoretical guidance for the application of CP-based spintronic devices. [ABSTRACT FROM AUTHOR]

• Utilizing telegraphic switching signal of MTJ for stochastic computing. • Roberts Cross operator designed by stochastic computing. • Roberts cross operator realized by simple logic using MTJ. • Edge detection results differ based on generated bit-stream length. A hardware method for image edge detection is proposed by using stochastic behavior of magnetic tunnel junction. Telegraphic switching property of magnetic tunnel junction is employed for obtaining random bits which allows constructing a circuitry of a probabilistic bit-stream generator for stochastic computing. By applying the Roberts cross operator, we develop a stochastic way for edge detection with approximation of image gradient, which successfully conducts the role of image edge detection. Different edge detection results for different bit-stream lengths are shown in order to suggest the optimal bit-stream length for operation. [ABSTRACT FROM AUTHOR]

• Electronic and atomic interactions inside the molecule impacted two ferromagnetic electrodes connected to the molecule. • Interaction of the electron with the nearest atom and neighboring electrons within the molecule Impacted the devices. • Biquadratic coupling between the neighboring atoms inside the molecule significantly impacted the spintronic device. Molecular spintronics devices (MSD) offer significant potential for next-generation computing and memory applications. In our prior experimental studies, we have utilized cubic Octametallic Molecular cluster composed of iron and Ni atoms without understanding different spin states the molecule can attain when covalently bonded with the two ferromagnetic electrodes. This study investigates the behavior of normalized molecular spin (S m) alongside three key variables: total system magnetization (M), molecular magnetization (M m), and free electron magnetization (F m), which represents the free electron component of local molecular magnetization, under various thermal energies. Using Monte Carlo simulations (MCS), we analyze these parameters within the framework of a magnetic tunnel junction-based molecular spintronics device (MTJMSD) composed of a cubic molecule. The focus is on the dependence of these four variables on biquadratic coupling strength (b m) and exchange couplings between localized atomic spin and nearest free electron spin (J e 0 m) , localized spin and free electron in the vicinity of nearest neighboring atom (J e 1 m) , two nearest free electrons (J eem). All the exchange couplings impact were studied at different thermal energies (kT). Our findings reveal complex interdependencies between these variables. For lower thermal energies (k T ≤ 0.1) , molecular spin decreased sharply with increasing bm , indicating molecular spin settling in low state. At higher thermal energies (k T = 0.5) , a non-monotonic relationship emerges with Sm peaking at intermediate bm values. Additionally, we observe that M increases more significantly with negative exchange couplings between local spin and free electron spin in the vicinity of nearest neighboring local spin at lower kT ; whereas positive magnitude of the same exchange coupling tends to stabilize the lower magnitude of M. Furthermore, the free electron spin (F m) increases with positive Jeem values, plateauing at higher coupling strengths and exhibiting a more gradual increase at higher temperatures. These results highlight the intricate balance between molecular coupling, exchange interactions, and thermal effects, providing critical insights for optimizing the performance and stability of molecular spintronic devices across different thermal energy regimes. [ABSTRACT FROM AUTHOR]

• Graphether is a semiconductor material that exhibits favorable characteristics for doping processes. • Stable P-type and N-type semiconductors were successfully synthesized through the process of doping. • A spin switch was devised based on the principle of electron tunneling spin filtering. • The resultant magnetic tunnel junction represents a high-efficiency single-channel spin switch. Spin switches are a fundamental component in the majority of spintronic devices, and have found extensive application in data storage, logical data manipulation, and signal processing. An essential aspect of constructing a spin switch is determining a stable two-dimensional material, which is easy to control and produce. Theoretical studies have shown that graphether is particularly promising due to its exceptionally high melting point and outstanding air stability. The band structure can be modified by doping, making it an important material for spin switch applications. In this paper, we have calculated the electromagnetic properties of doped graphether by first principles. Then we select a modified graphether with P-type and N-type doping configurations to construct magnetic tunnel junctions (MTJ). The results show that the MTJ exhibits perfect highly efficient spin switch as a result of spin reversal induced by spin-transfer torque (STT). In addition, our designed MTJ shows a remarkable rectification effect and spin filtering effect (SFE). According to our calculations, the modified graphether materials also show promise as two-dimensional spintronics materials. [ABSTRACT FROM AUTHOR]

• In this work, we studied MTJs based on thin film and complete Heusler alloy as electrodes and WSe 2 2D material as tunneling barrier. • The proposed MTJ exhibits advantages over conventional materials like transition metals (Fe, Co, Ni) with metal oxides (MgO, Al 2 O 3). • The obtained TMR values of the proposed MTJ with a single layer of WSe 2 is as high as 1.75 lakh %, which is a very high value (order of 5). This paper presents a Magnetic Tunnel Junction (MTJ) based on Co 2 FeAl Heusler alloy and 2D material WSe 2 with an enhanced tunnelling magneto-resistance (TMR). Our study is inspired by recent investigations of 2D materials and Heusler alloys. By employing static Density Functional Theory (DFT) simulations coupled with Non-Equilibrium Green's Function (NEGF) transport models, we evaluate conductance properties in Co 2 FeAl/WSe 2 /Co 2 FeAl MTJ. The half metallicity of Co 2 FeAl and quantum confinement properties of WSe 2 are compatible, which enhances the TMR of MTJ. [ABSTRACT FROM AUTHOR]

The tunneling magnetoresistance (TMR) magnetic sensor offers numerous advantages, including high response speed, strong anti-interference capability, high reliability, and ease of integration. Despite the challenges associated with generating high-frequency alternating magnetic fields, we have investigated the frequency response characteristics of a self-developed TMR magnetic sensor (TMR-MS) with highly sensitive properties of approximately 430mV/V/Oe and a detection limit of 340 pT/Hz 1 2 . Through experimental testing for frequency response, our TMR-MSs demonstrate exceptional fast response capabilities across temperatures ranging from -30 °C to 50 °C. These experimental results highlight the significant potential of TMR-MS with highly sensitive properties for industrial applications. • TMR-MS has numerous advantages: Fast, reliable, anti-interference, easy integration. • Highly sensitive: 430 mV/V/Oe. Detection capability: 340 pT/Hz 1 / 2. • Robust performance: TMR-MS maintains fast response (-30 °C to 50 °C). • Industrial potential: Highly sensitive TMR-MS suits demanding environments. [ABSTRACT FROM AUTHOR]

• High B2 ordering parameter was observed in Co 2 FeAl x Si 1– x thin films. • Magneto-crystalline anisotropy constant K 1 changed as Al component x increased in Co 2 FeAl x Si 1– x thin films. • Magneto-crystalline anisotropy constant K 1 crossed K 1 = 0 line at around x = 0.33. A tunnel magnetoresistance (TMR) sensor is a highly sensitive magnetic sensor workable at room temperature. To achieve smaller magnetic field detection, both a high TMR ratio and small magnetic anisotropy of the free layer are required. In this study, we developed single crystalline Co-based Heusler alloy Co 2 FeAl x Si 1- x films as the free layer of TMR sensors and systematically investigated their crystalline and magnetic properties. The magnetic tunnel junction (MTJ) with these alloys is a promising device for highly sensitive TMR sensors due to their half-metallicity. We evaluated the B2 and L2 1 ordering parameters S B2 and S L21. S B2 was above 80 % for all the samples and S L21 was 48 % at a maximum, which indicates that all the samples exhibit half-metallicity. In addition, we evaluated their first magneto-crystalline anisotropy constant K 1 from magnetization curves. K 1 changed from positive to negative as Al component x increases and K 1 was about 1200 erg/cc at x = 0.33. These results indicate that Co 2 FeAl x Si 1- x films around x = 0.33 have a good candidate for the free layer of TMR sensors because of their half-metallicity and small magnetic anisotropy. [ABSTRACT FROM AUTHOR]

• Thermoelectric effects of resonant-tunneling MTJs (RTMTJs) are investigated theoretically. • There are β-Ga 2 O 3 , ZnO and a non-magnetic metal as quantum well between the MgO barriers. • Improvements in the thermoelectric features are achieved in the RTMTJs based on β-Ga 2 O 3. A study was conducted to investigate thermoelectric effects (TEEs) in resonant-tunneling magnetic tunnel junctions (RTMTJs) featuring wide-bandgap semiconductors such as ZnO and β-Ga2O3, along with a non-magnetic metal spacer. The transmission function was determined using the non-equilibrium Green's function method within a tight-binding model. Significant enhancements in TEEs were observed for the β-Ga2O3 semiconductor compared to other materials, indicating its potential applicability in the emerging field of β-Ga2O3 spincaloritronics. [ABSTRACT FROM AUTHOR]

• The operation stability of PMA structures with different HMs were investigated. • The appropriate HM and structure can enhance the thermal stability of PMA. • The thermally robust PMA was obtained in the Co-rich CoFeB composition. For magnetic sensor and magnetic random access memory, the thermally tolerant need to be improved at a relatively high operation temperature. In this work, the correlations between the thermal stability and perpendicular magnetic anisotropy films with different heavy metal layers, structures and CoFeB compositions were investigated in details. It was found that the thin films adopting W or Mo heavy metal layer in the bottom structure, and the thin films adopting Mo heavy metal layer in the top structure exhibit a relatively good operation stability, no matter what the CoFeB composition is. Moreover, the thermally robust perpendicular magnetic anisotropy was obtained in the CoFeB with a relatively large Co atomic composition. According to the element distribution states analysis and oxidation conditions at CoFeB/MgO interface, the reasons are attributed to the structural- and composition-dependent Fe-O bonding. This research helps to design and optimize the ultra-low-power and thermally stable magnetic devices based on the suitable heavy metal layers, structures, and CoFeB compositions. [ABSTRACT FROM AUTHOR]

• A strategy to realize nonvolatile magnetization reversal is proposed based on electric field control of interlayer coupling. • The dependence of interlayer coupling energy on electric field strength follows a continuous odd function in mathematics, guaranteeing the nonvolatility. • The feasibility of this strategy is demonstrated by a MnBi 2 Te 4 / h -BN/Fe 3 GaTe 2 / h -BN/MnBi 2 Te 4 junction. Achieving electric field control of nonvolatile magnetization reversal in van der Waals magnetic tunnel junctions (vdW MTJs) is of paramount importance for nanoscale spintronic devices with ultralow-power consumption and high-density storage. Here, a new and universal design strategy is proposed to realize nonvolatile magnetization reversal, which is based on electric field control of interlayer coupling. The nonvolatility benefits from the proposed special principle of vdW MTJ, in which the dependence of interlayer coupling energy on electric field strength follows a continuous odd function in mathematics. The feasibility of proposed strategy is proved by the MnBi 2 Te 4 / h -BN/Fe 3 GaTe 2 / h -BN/MnBi 2 Te 4 junction. The magnetization state of Fe 3 GaTe 2 can be reversed 180° by changing electric field directions. Moreover, the magnetization states can be preserved after removing electric field, demonstrating the nonvolatile magnetization reversal. Therefore, the present strategy provides an alternative approach to realize electric control of nonvolatile magnetization reversal in vdW MTJs for next-generation spintronic devices. [ABSTRACT FROM AUTHOR]

• This article proposes new logic gates based on four-channel magnetic cell (mcell) with new magnetic logic (mlogic) called multilevel cell gate (MLC Gate). • In order to design the proposed gate circuit, MLC Gate is used magnetic gate (MGate) basic structure to reduce heat losses, Spin Based Electronic Gate (SBEG) structure to reduce the number of mcells and create a neural network, and finally the multi-level property of voltage-controlled spin orbit torque-memory (MV-SOTM) cells to reduce energy consumption. • mcell with mlogic proposed in this article has only four bases. The two writing paths of the mcell are composed of two layers with constant magnetization, which are made in two opposite directions to align the direction of the electric current with the direction of the domain wall field. The two reading paths of the mcell are made of two MTJ magnetic cells in series. So that the variable ferromagnetic layer of these two MTJ cells is isolated under the influence of the domain wall field by an insulating layer of Mgo. • One of the advantages of multi leveling mcell is increasing the working frequency to an acceptable value and in this article, the use of the voltage controlled magnetic anisotropy (VCMA) method is well stated to describe the reduction of the critical switching current. Spintronics is an emerging technology for designing logic circuits. The non-volatile logic based on the magnetic tunnel junction (MTJ) cell is a suitable solution to overcome the leakage power problem, which has become a major obstacle for CMOS technology. Here, we introduce a new style of magnetic gate (mGate) logic, which is built by a four-terminal cell. This cell operated by motion of domain wall that is based on spin transfer torque (STT) in a multi-level cell (MLC) structure. To reduce the complexity, a static circuit with a resistive load in ratioed logic style has been used. The use of MLC Gate logic in the static ratioed logic circuit is a suitable solution to reduce the complexity level of structure and power consumption in logic circuits in the field of spintronics. The performance of different magnetic logic gates have been investigated by simulations. The simulation results show that the MLC Gates offer a smaller area and lower power consumption and lower energy in comparison with the previous mGate and magnetic computing in memory. [ABSTRACT FROM AUTHOR]

• The pristine bilayer NiBr 2 is an A-type antiferromagnetic semiconductor, which becomes a ferromagnetic half-metal under electron doping. • Li intercalation also can induce a similar magnetic transition along with a electron transition from the semiconductor to half-metal. • We design a magnetic tunnel junction based on bilayer NiBr 2 , showing a giant tunnel magnetoresistance up to 1.7 × 1011 100%. Two-dimensional bilayer materials, such as twisted bilayer graphene, are promising for device applications due to their tunable and controllable electronic properties. Here, we propose to modify the magnetic properties of the bilayer NiBr 2 with electron doping using first-principles calculations. Our results show that the pristine bilayer NiBr 2 is an A-type antiferromagnetic (AFM) semiconductor, which becomes a ferromagnetic (FM) half-metal under electron doping. Such transition is caused by lower electronic state occupation at the band edge. Instead of electrostatic doping, the intercalation of the alkali metal lithium can induce the same magnetic phase transition. Finally, a magnetic tunnel junction based on bilayer NiBr 2 is designed, showing giant tunnel magnetoresistance up to 1.7 × 1011 %. These results offer fresh perspectives on the application of antiferromagnetic bilayer materials for spintronic devices. [ABSTRACT FROM AUTHOR]

• A novel magnetic sensor with sub-10 nm thickness and GHz operation is proposed. • Lateral spin valve terminates in a magnetic tunnel junction with a SAF free layer. • Interaction of interlayer dipole & exchange couplings with STT switching examined. • SNR above 20 dB has been achieved with current density of 107 A/cm2 or less. We present a new magnetic sensor design using a lateral spin valve (LSV) structure that features a sensing end less than 10 nm thick, making it suitable for integration with nanoscale devices. Shot noise reduction and signal-to-noise ratio (SNR) improvement under gigahertz operation are expected for our design. The spin detection part of the LSV forms a magnetic tunnel junction (MTJ) beneath the aluminum channel. We propose to replace the single layer ferromagnet in the spin detection part of the LSV with a synthetic antiferromagnetic structure: this facilitates spin-transfer torque (STT) induced magnetization switching. Macrospin simulation shows that interlayer magnetic dipole coupling helps STT switching while interlayer exchange coupling hurts, owing to their different precession symmetries in the out-of-plane direction. It also shows that SNR > 20 dB can be achieved for a pseudorandom binary sequence with a minimum bit length 0.5 ns. [ABSTRACT FROM AUTHOR]

• Mo capped pMTJs show high TMR and thermal stability. • Above ∼35 nm H c is size-independent. • The VCMA effect is present even at 20 nm diameters. Co 20 Fe 60 B 20 /MgO/Co 20 Fe 60 B 20 perpendicular magnetic tunnel junctions with Mo seed and capping layers were patterned into sub-100 nm diameter devices. The resulting devices were imaged in plan view by scanning electron microscopy and in cross-section by scanning transmission electron microscopy. The tunnel magnetoresistance was ∼125%. The coercivity dropped off below 35 nm, and the stray field increased with decreasing diameter. The voltage controlled magnetic anisotropy effect was observed for all sizes, though it was convoluted with thermal and stray field effects for the smaller diameters. [ABSTRACT FROM AUTHOR]

Highlights • We study annealing effect on memory states stability in CoFeB/MgO/CoFeB based perpendicular MTJs. • Our study indicates a ferromagnetic coupling between the storage and reference layers. • Enhance pMTJs stability by playing perpendicular magnetic anisotropy and interlayer coupling. Abstract Perpendicular magnetic tunnel junctions (p-MTJs) attract great interest because of their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). The annealing process is critical to achieve the required structural and magnetic properties, therefore obtaining high perpendicular tunneling magnetoresistance (p-TMR) and lower switching current. In this work, the CoFeB/MgO/CoFeB-based p-TMR stack was prepared and a high p-TMR value of 155.9% was obtained from CIPT. The p-MTJs were patterned with pillar sizes ranging from 50 nm to 1000 nm and were annealed upon different annealing temperatures (T A) of 300 and 340 °C. The resistance at parallel (R P) and antiparallel (R AP) state in p-MTJs was obtained upon the application of a ±30 mT perpendicular magnetic field, where the angle of magnetization between storage and reference layer at memory state, θ P and θ AP , were derived from the P and AP resistance ratios with and without magnetic field. The condition θ P = θ AP of about 63.5° was found in as-deposited samples, indicating a ferromagnetic interlayer coupling between storage and reference layers, where θ P = 0° and θ AP = 180° at T A = 300 °C and 340 °C demonstrate a stable memory state. The stability of the resistance state was modeled by considering the evolution of effective perpendicular magnetic anisotropy (K eff) and interlayer coupling constant (J), showing a method to evaluate the ratio of K eff / J via the memory state resistance characterization, where the K eff / J of about −1.26 was obtained in our as-deposited samples. Our study assesses the effect of T A on the θ P and θ AP and supplies the method to enhance the stability through the optimization of perpendicular magnetic anisotropy and interlayer coupling, so to better control the performance of p-MTJ-based STT-MRAMs. [ABSTRACT FROM AUTHOR]

Highlights • A Ni/Gr/h-BN/Gr/Ni nanostructure was constructed and its spin-dependent transmission properties were simulated. • This device combines the spin filtering of Gr/FM interface and the resonant tunneling of Gr/h-BN/Gr heterostructure. • An effective approach was demonstrated to control spin current based on the bias tunability of the resonance tunneling. • Spin resonance results in a large magnetoresistance and negative differential resistance in the device. Abstract Future development of spintronic devices urgently requires an advanced control method of spin current. Combining graphene with other various characteristic two-dimensional crystals in different ways can produce a new class of functional materials, which offers a unique platform for spintronics. A specific van der Waals heterostructure consisting of graphene and hexagonal boron nitride (h-BN) as the barrier layer in magnetic tunnel junctions (MTJs) is proposed in this paper. This heterostructure device combines the strong spin filtering effect of graphene/ferromagnet interface and the resonant tunneling effect of graphene/h-BN/graphene van der Waals heterostructure. We demonstrate an effective approach to control spin current based on the bias tunability of the spin resonance tunneling transport. Theoretical research unambiguously reveals that spin resonance appears when the electronic spectra of spin electron in two graphene layers are aligned, which results in a large magnetoresistance and negative differential resistance in the device. The efficient bias controllability of spin current, combined with the excellent magnetoresistance behavior, can be the key building blocks in future spin-based magnetic detection and high-frequency logic devices. [ABSTRACT FROM AUTHOR]

The thermal spin-transfer torque (TSTT) and Seebeck coefficients (SECs) are investigated for diverse superlattice magnetic tunnel junctions (DS-MTJs) including linear, Gaussian, Lorentzian, and Pöscl-Teller profiles. The present study is done in the linear response theory. The higher TSTT and SECs are found for the DS-MTJs in comparison with those for the regular types. The results can be utilized to improve in the fields of spintronics and spincaloritronics. [ABSTRACT FROM AUTHOR]

Recently there is considerable interest to realize efficient and low-cost true random number generators (RNGs) for practical applications. One important way is through the use of bistable magnetic tunnel junctions (MTJs). Here we study the magnetization dynamics of an MTJ, with a focus to realize efficient random bit generation under the assumption that the orientation dependence of the energy of the nanomagnet is described by two perpendicular in-plane anisotropies. We find that a high rate of random bit generation is achievable away from the pure easy-axis situation by tuning a single parameter H z so that it is either (a) toward a barrierless-like single easy plane situation when H z reduces to zero, or (b) toward a stronger easy plane situation when H z becomes increasingly negative where transitions between low energy states are confined in the stronger easy plane that contains the saddle points. We find that the MTJs maintain their fast magnetization dynamical characteristics even in the presence of a magnetic field. Our findings provide a valuable guide to achieving efficient generation of probabilistic bits for applications in probabilistic computing. • The switching dynamics of a nanomagnet for probabilistic computing is studied. • We interpret an energy expression that controls the switching dynamics. • We employ the Fokker-Planck equation to study the dynamics of the system. • The parameter H_z is tuned to achieve the fastest switching dynamics. • An ultrafast random switching is demonstrated for probabilistic computing. [ABSTRACT FROM AUTHOR]

In our JunPy package, we have combined the first-principles calculated self-consistent Hamiltonian with divide-and-conquer technique to successfully determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction (MTJ). We propose a comprehensive analytical derivation to clarify the crucial roles of spin–orbit coupling that mediates the exchange and spin–orbit components of spin torque, and the kinetic and spin–orbit components of spin current accumulation. The angular dependence of cumulative spin–orbit torque (SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of magnetic moments of the free Fe layers. Different from the conventional MA energy calculation and the phenomenological theory for a whole MTJ, our results provide insight into the orbital-resolved SOT for atomistic spin dynamics simulation in emergency complex magnetic heterojunctions. • Theory of spin torque and spin current for first-principles calculations is derived. • Exchange spin torque is clarified by spin–orbit torque and spin current accumulation. • Current-driven spin-transfer torque in magnetic tunnel junction is studied. • Interfacial spin–orbit torque could determine magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Highlights • Magnetic tunnel junction comprised of free Heusler alloy and pinned CoFe • Finite open-circuit voltage develops on the order of several 10 μ V in the anti-parallel state • Reversal of magnetic dipolar field generates an electromotive force of order 10 μ V Abstract We investigate the tunneling magnetoresistance (TMR) of the magnetic tunnel junction (MTJ) comprised of the Heusler alloy ( Co 2 MnSi) and the pinned CoFe to probe the spin polarization of Co 2 MnSi. From the TMR value thus obtained, we estimate 40 % polarization of Co 2 MnSi , much less than 100 % expected for the suspected half metal. Remarkably, upon applying the weak switching magnetic field to the MTJ in the parallel state, our system exhibits a finite open-circuit voltage on the order of several 10 μ V in the anti-parallel state. We have demonstrated that the reversal of magnetic dipolar field induced by the Heusler alloy as a free layer can generate an electromotive force of the same order and can clearly explain the observed polarity and sample size dependence of the voltage offset at zero bias current. [ABSTRACT FROM AUTHOR]

Highlights • Thermoelectric (TE) of double-barrier MTJs (DBMTJs) are studied in linear response regime. • There is a semiconductor (InP) as a quantum well between MgO insulators. • The TE effects of the DBMTJs enhance compared to those of the single-barrier MTJs. • Spin-dependent TE effects is also investigated in the DBMTJs. • Effects of different contacts and Rashba spin-orbit coupling are studied too. Abstract Thermoelectric effects of CoFeB/MgO/InP/MgO/CoFeB double-barrier magnetic tunnel junctions (DBMTJs) are presented in the linear response regime. The nonequilibrium Green’s function (NEGF) formalism is used within the effective mass approximation. There are descriptions of temperature and angular dependence for thermoelectric properties. The results show an enhancement in the DBMTJs thermoelectric compared to single-barrier MTJs due to the resonant tunneling effect through the DBMTJs. It is also found that the Seebeck coefficients may be increase in asymmetric DBMTJs. Effects of the temperature and magnetization alignments on the spin-dependent Seebeck coefficients are also described. Finally, the Seebeck coefficients are investigated considering the Rashba spin-orbit coupling at the insulator/semiconductor interfaces. [ABSTRACT FROM AUTHOR]

Fe 3 O 4 nanoparticles have been made by a co-precipitation method with an average size of 13 nm. Raman measurements show that there is also a small fraction of maghemite that is not seen in the XRD data. The saturation magnetization is high for this preparation method and the coercive field is low at 300 K. The high field magnetic moment cannot be fitted to a Bloch temperature dependence over the full temperature range, which is likely due to the effect of the Verwey transition at 120 K. Pressed powders shows a magnetoresistance of up to −6.5% at 8 T and 300 K. The magnetoresistance can be fitted to a model where there is a spin-dependent tunnelling between nanoparticles with a spin-disordered shell. The temperature dependence of the resistivity can be attributed to nanoparticle electrostatic charging effects. [ABSTRACT FROM AUTHOR]

The optical, magnetooptical, electrical, and magnetic properties of La 0.67 Ba 0.33 MnO 3 films grown on the SrTiO 3 and ZrO 2 (Y 2 O 3 ) substrates have been studied. The temperature and magnetic field dependences of magnetotransmission of light in the La 0.67 Ba 0.33 MnO 3 /ZrO 2 (Y 2 O 3 ) film with a variant structure exhibit features which can be attributed to an optical response to tunnel magnetoresistance – tunnel magnetotransmission. Unlike the optical response to colossal magnetoresistance, existing near the Curie temperature only, the tunnel magnetotransmission increases at T  → 0 K, has a complex hysteresis behavior with the change of sign of the effect, and saturates in magnetic fields above 1 kOe. The observed tunnel magnetotransmission has been interpreted within the magnetorefractive effect theory developed for granular films. [ABSTRACT FROM AUTHOR]

In conventional magnetic devices such as magnetic tunnel junctions, a steady oscillation of a soft layer magnetization could find its application in various electronic systems. However, these devices suffer from their low output signal and large spectral linewidth. A more elegant scheme based on domain wall oscillation could be a solution to these issues if DW dynamics could be controlled precisely in space and time. In fact, in DW devices, the magnetic configuration of domain wall and its position are strongly dependent on the device geometry and material properties. Here we show that in a constricted device with judiciously adjusted dimensions, a DW can be trapped within the central part and keep oscillating with a single frequency f . For 200 nm by 40 nm nanowire, f was found to vary from 2 GHz to 3 GHz for a current density between 4.8 × 10 12  A/m 2 and 5.6 × 10 12  A/m 2 . More interestingly, the device fabrication is simply based on two long nanowires connected by adjusting the offset in both x and y directions. This new type of devices enables the conversion of dc-current to an ac-voltage in a controllable manner opening thus the possibility of a new nano-oscillators with better performance. [ABSTRACT FROM AUTHOR]

Due to the theoretical prediction of large tunneling magnetoresistance (TMR), graphene-based magnetic tunneling junction (MTJ) has become an important branch of high-performance spintronics device. In this paper, the non-collinear spin filtering and transport properties of MTJ with the Ni/tri-layer graphene/Ni structure were studied in detail by utilizing the non-equilibrium Green’s formalism combined with spin polarized density functional theory. The band structure of Ni–C bonding interface shows that Ni–C atomic hybridization facilitates the electronic structure consistency of graphene and nickel, which results in a perfect spin filtering effect for tri-layer graphene-based MTJ. Furthermore, our theoretical results show that the value of tunneling resistance changes with the relative magnetization angle of two ferromagnetic layers, displaying the anisotropic tunneling behavior of graphene-based MTJ. This originates from the resonant conduction states which are strongly adjusted by the relative magnetization angles. In addition, the perfect spin filtering effect is demonstrated by fitting the anisotropic conductance with the Julliere’s model. Our work may serve as guidance for researches and applications of graphene-based spintronics device. [ABSTRACT FROM AUTHOR]

Molecular bridges covalently bonded to two ferromagnetic electrodes can transform ferromagnetic materials and produce intriguing spin transport characteristics. This paper discusses the impact of molecule induced strong coupling on the spin transport. To study molecular coupling effect the octametallic molecular cluster (OMC) was bridged between two ferromagnetic electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the exposed side edges. OMCs induced strong inter-ferromagnetic electrode coupling to yield drastic changes in transport properties of the magnetic tunnel junction testbed at the room temperature. These OMCs also transformed the magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic resonance studies provided insightful data to explain transport studies on the magnetic tunnel junction based molecular spintronics devices. [ABSTRACT FROM AUTHOR]

Electric-controlled magnetization precession introduces technologically relevant possibility for developing spin torque nano-oscillators (STNO) with potential applications in microwave emission. Using the perpendicularly magnetized magnetic tunnel junction (MTJ), we show that the magnetization oscillation frequency can be tuned by the co-action of electric field and spin polarized current. The dynamical phase diagram of MTJ-based STNO is analytically predicted through coordinate transformation from the laboratory frame to the rotation frame, by which the nonstationary out-of-plane magnetization precession process is therefore transformed into the stationary process in the rotation frame. Furthermore, using this STNO as a microwave source, we numerically demonstrate that the bit signal can be transmitted by a binary frequency shift keying (BFSK) modulation technique. The BFSK scheme shows good modulation features with no transient state. [ABSTRACT FROM AUTHOR]

This paper presents a steady auto-oscillation in a spin-torque oscillator using MgO-based magnetic tunnel junction (MTJ) with a perpendicular polarizer and a perpendicular free layer. As the injected d.c. current varied from 1.5 to 3.0 mA under a weak magnetic field of 290 Oe, the oscillation frequency decreased from 1.85 to 1.3 GHz, and the integrated power increased from 0.1 to 74 pW. A narrow linewidth down to 7 MHz corresponding to a high Q factor of 220 was achieved at 2.7 mA, which was ascribed to the spatial coherent procession of the free layer magnetization. Moreover, the oscillation frequency was quite sensitive to the applied field, about 3.07 MHz/Oe, indicating the potential applications as a weak magnetic field detector. These results suggested that the MgO-based MTJ with perpendicular magnetic easy axis could be helpful for developing spin-torque oscillators with narrow-linewidth and high sensitive. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optical writing and electrical reading of magnetic states within nanoscale ferromagnetic tunnel junctions. • Downscaling of the perpendicularly magnetized nanodevices while retaining the desired functionalities. • Correlation between the switching probability, magnetic anisotropy, and the diameter of the nanodevices. • Probing the depth-resolved hysteresis and time-resolved magnetization dynamics in a full stack magnetic tunnel junction film. Magnetic tunnel junctions (MTJs) are elementary units of magnetic memory devices. For high-speed and low-power data storage and processing applications, fast reversal of the magnetization by an ultrashort laser pulse is extremely important. We demonstrate single-shot switching of Tb/Co-multilayer based nanoscale MTJs by combining the optical writing and the electrical read-out methods. A 90-fs-long laser pulse switches the magnetization of the storage layer (SL). The change in the tunneling magnetoresistance (TMR) between the SL and a reference layer (RL) is probed electrically across the oxide barrier. Single-shot switching is demonstrated by varying the cell diameter from 300 nm to 20 nm. The anisotropy, magnetostatic coupling, and switching probability exhibit cell-size dependence. By suitable association of laser fluence and magnetic field, successive commutation between high-resistance and low-resistance states is achieved. The nature of the magnetization reversal of both SL and RL in a continuous film is probed with a depth-resolved magneto-optical Kerr effect (MOKE) magnetometry. The ultrafast dynamics in the continuous full-MTJ stack is investigated with the time-resolved pump–probe technique. Our experimental findings provide strong support for the growing interest in ultrafast spintronic devices. [ABSTRACT FROM AUTHOR]

• Researches into the intrinsic MTJ noise are essential to enhance the TMR detectivity. • An equivalent noise model to deal with the experimental output is proposed. • The model demonstrates noise sources and transfer functions in a measurement system. • The model provides an effective way to obtain the intrinsic MTJ noise. The intrinsic noise of magnetic tunneling junctions (MTJs) limits the detectivity of tunneling magnetoresistance (TMR) sensors, as a key factor. Therefore, researches into the intrinsic MTJ noise are essential to enhance the TMR detectivity. However, the noise measurement result of the MTJ elements usually deviates from the intrinsic noise, especially when the MTJ resistance exceeds the range of impedance matching. This deviation results in the difficulty to enhance the TMR detectivity efficiently. In this paper, we propose an equivalent noise model to deal with the deviation between the output and the intrinsic noise. The model demonstrates the noise sources and the corresponding transfer functions in a normal noise measurement system. After calibrating the model parameters, we extract the thermal noise of some metal film resistors based on the model to indicate the model's reliability. Furthermore, we apply the model to extract the intrinsic noise of MTJ elements with different resistances. The result indicates it is realizable to measure the intrinsic MTJ noise without considering the MTJ resistance range. Our work provides an effective way to obtain the intrinsic MTJ noise from the experimental output, which is important for the noise investigation on TMR sensors. [ABSTRACT FROM AUTHOR]

Voltage-controlled magnetoresistive random access memory (VC-MRAM) based on voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a promising ultimate non-volatile memory with ultralow power consumption. However, the dynamic switching in a conventional MTJ is accompanied by a relatively high write error rate (WER), hindering the reliable operation of VC-MRAM. Here, we propose a reliable writing scheme using the in-plane demagnetizing field (IDF) and voltage-induced negative out-of-plane anisotropy field (NOAF). Numerical simulations based on macrospin model demonstrate that the voltage induced NOAF modifies the switching dynamics and increases the torque due to the IDF, thereby reducing the switching time. The IDF and voltage-induced NOAF also reduce the mean energy difference between the magnetization direction at the end of the pulse and the equilibrium direction. As a result, an appropriate combination of the IDF and voltage-induced NOAF reduces the WER by one order of magnitude compared with that of the dynamic switching in a conventional MTJ. • Voltage-controlled MRAM is an emerging ultralow-power non-volatile memory. • We propose a reliable writing scheme. • The scheme uses shape- and voltage-induced uniaxial anisotropy. • Write error rate reduced by one digit compared with the conventional writing scheme. [ABSTRACT FROM AUTHOR]

The interface formation in epitaxial MgO / Co 2 MnSi ( 001 ) films was studied using in-situ X-ray photoelectron spectroscopy (XPS). MgO was deposited on single crystal Co 2 MnSi ( 001 ) layers using e-beam evaporation: a technique which is expected to oxidize the Co 2 MnSi layer somewhat due to the rise in oxygen partial pressure during MgO deposition while leaving the deposited MgO oxygen deficient. Not unexpectedly, we find that e-beam evaporation of MgO raises the oxygen background in the deposition chamber to a level that readily oxidizes the Co 2 MnSi surface, with oxygen bonding preferentially to Mn and Si over Co. Interestingly, this oxidation causes an elemental segregation, with Mn-Si effectively moving toward the surface, resulting in an MgO / Co 2 MnSi interface with a composition significantly differing from the original surface of the unoxidized Co 2 MnSi film. As MgO is deposited on the oxidized Co 2 MnSi , the Mn-oxides are reduced, while the Si oxide remains, and is only somewhat reduced after additional annealing in ultrahigh vacuum. Annealing after the MgO is grown on Co 2 MnSi causes oxygen to move away from the oxidized Co 2 MnSi interface toward the surface and into the MgO. This observation is consistent with an increase in the tunneling magnetoresistance ratio with post-growth annealing measured in fabricated magnetic tunnel junctions (MTJs). The findings are discussed in light of fabrication of MgO/Heusler based MTJs, where the exponential decay of tunneling probability with contact separation exemplifies the importance of the ferromagnet/tunnel barrier interface. [ABSTRACT FROM AUTHOR]

The electronic, magnetic and transport properties of oxygen or magnesium vacancies at the FeRh/MgO/FeRh (0 0 1) magnetic tunnel junction are studied within first principles. Configurations with one O or Mg vacancy per C (2 × 2) surface unit cell, which is located in the MgO interfacial layers, are investigated. We observed that the O and Mg vacancies defect have a very little influence on the magnetic state of the spacer. Very interestingly, the Fe atoms exhibit an enhanced magnetic moment in the case of Mg-vacancy, this latter was found to decrease in the case of O-vacancy. The variations in the spin polarization and magnetic moment values for Fe and Rh atoms at the interface were found to be larger in presence of Mg vacancy. An analysis of the charge densities of our systems was also performed; large variations in the Mg-vacancy system were observed. This affects more the t 2 g states of the interfacial Fe atom. Moreover, we present an ab initio calculated transmission and I-V characteristics for FeRh/MgO/FeRh (0 0 1) magnetic tunnel junction and we compare results to those of O and Mg-vacancy at the interface using the TRANSIESTA code, which combines the DFT electronic structure calculations with the non-equilibrium Green function formalism (NEGF) for transport properties. The results show that the zero-bias minority spin transmission is much larger than the majority spin transmission for all structures. In all systems and for all magnetic configurations, minority spin currents are higher than majority spin ones, this means that transport properties are, mainly, determined by minority spin channel. [ABSTRACT FROM AUTHOR]

We present a study of perpendicular magnetic anisotropy in [Co/Ni( t )/Co/Pt] ×8 multilayers for use as free layers in magnetic tunnel junctions (MTJ) and spin valves. The thickness t of the Ni sub-layer was varied and the resulting magnetic properties were investigated. As determined from magnetic force microscopy and magnetometry measurements, all multilayers exhibited a perpendicular magnetic anisotropy with an increase of saturation magnetization with thickness t . From the temperature dependence of the magnetization, well described by a Bloch law, we find that the spin-wave stiffness constant of the [Co/Ni( t )/Co/Pt] ×8 multilayers is larger compared to (Co/Ni) multilayers. These multilayers could be the basis for spintronic devices where the reduction of total Pt content could help to reduce the damping constant while keeping the magnetic anisotropy energy relatively high. These are conflicting requirements needed for high performance magnetic memory devices. [ABSTRACT FROM AUTHOR]

The transport properties of GaAs nanowire (NW)-based devices are investigated using non-equilibrium Green’s function technique combined with density functional theory (DFT). Two types of NW-based devices are studied, which include the electrodes that are made of half-metallic GaMnAs NWs grown along the [0 0 0 1] direction, and the scattering region that consists of a tunneling structure (GaMnAs/GaAs/GaMnAs) or a conducting structure (GaMnAs/GaAs:Be/GaMnAs), respectively. The proposed nanostructures both exhibit robust transport properties including spin-filtering, negative differential resistance (NDR) and giant magnetoresistance (GMR) effects, which are further analyzed with carrier channels and transmission spectra. These structures imply potential applications for low dimensional semiconductor spintronic devices such as spin valve. [ABSTRACT FROM AUTHOR]

CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ’s) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L1 0 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular Co x Pd alloy-pinned Co 20 Fe 60 B 20 /MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the Co x Pd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied Co x Pd MTJ stacks. The Co x Pd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO 2 /MgO (13)/Co X Pd 100−x (50)/Ta (0.3)/CoFeB (1)/MgO (1.6)/CoFeB (1)/Ta (5)/Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 °C for 5 min. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]

We study the influence of the perpendicular magnetic anisotropy on the voltage-induced ferromagnetic resonance in magnetic tunnel junctions (MTJs). An MTJ response to the applied radio-frequency voltage excitation is investigated using micromagnetic calculations with the free layer oriented both in-plane and out-of-plane. Our model allows for a quantitative description of the magnetic system parameters such as resonance frequency, sensitivity or quality factor and for a distinction between material-dependent internal damping and disorder-dependent effective damping. We find that the sensitivity abruptly increases up to three orders of magnitude near the anisotropy transition regime, while the quality factor declines due to effective damping increase. We attribute the origin of this behaviour to the changes of the exchange energy in the system, which is calculated using micromagnetic approach. [ABSTRACT FROM AUTHOR]

The state diagram of a magnetic tunnel junction with perpendicularly magnetized electrodes in the presence of spin-transfer torques is computed in a macrospin approximation using a power dissipation model. Starting from the macrospin's energy we determine the stability of energy extremum in terms of power received and dissipated, allowing the consideration of non-conservative torques associated with spin transfer and damping. The results are shown to be in agreement with those obtained by direct integration of the Landau-Lifshitz-Gilbert-Slonczewski equation. However, the power dissipation model approach is faster and shows the reason certain magnetic states are stable, such as states that are energy maxima but are stabilized by spin transfer torque. Breaking the axial system, such as by a tilted applied field or tilted anisotropy, is shown to dramatically affect the state diagrams. Finally, the influence of a higher order uniaxial anisotropy that can stabilize a canted magnetization state is considered and the results are compared to experimental data. [ABSTRACT FROM AUTHOR]

• Total ionizing dose effect on the voltage-controlled magnetic anisotropy Hall bar device based on HfZrO/CoFeB hybrid film. • Voltage-controlled magnetic anisotropy effect is enhanced with the accumulation of irradiation dosage. • The proposed mechanism focus on interfacial trapped charges. • HfZrO/CoFeB hybrid film possess potential for radiation-hard memory. We investigate the total ionizing dose (TID) effect on the voltage-controlled magnetic anisotropy (VCMA) Hall bar device based on HfZrO/CoFeB hybrid film. Devices under test are exposed to 1.17 MeV 60Co γ-ray at the dose rate of 50 rad(Si)/s. The Anomalous Hall measurement is performed at several certain irradiation dosages. The results show that the VCMA effect is enhanced with the accumulation of irradiation dosage. We propose a mechanism of interface trapped charges to explain this phenomenon. Thus, our work indicates that the magnetic tunneling junction based on HfZrO/CoFeB hybrid film is a promising building block for radiation-hard VCMA-MRAM (magneto-resistive random-access memory). [ABSTRACT FROM AUTHOR]

Perpendicular magnetic anisotropy (PMA) is a key property of magnetoresistive random access memory (MRAM). To increase areal density of MRAM it is important to find a way to enhance the PMA. Recently a strong enhancement of the PMA by inserting an ultrathin LiF layer at an Fe/MgO interface was reported [T. Nozaki et al., NPG Asia Materials (2022) 14: 5]. To understand the origin of the observed enhancement of the PMA we perform first-principles calculations of magnetocrystalline anisotropy energy (MAE) of the following four kind of multilayer structures: Fe/MgO, Fe/LiF/MgO, Fe/FeO/MgO, and Fe/FeF/LiF/MgO. We find that the MAEs of the Fe/LiF/MgO and the Fe/FeF/LiF/MgO structures are almost the same as that of the Fe/MgO structure, while the MAE of the Fe/FeO/MgO structure is less than a half of that of the Fe/MgO structure. The results show that the major origin of the enhancement of the PMA obtained by inserting an ultrathin LiF layer at an Fe/MgO interface is the suppression of the mixing of Fe and O atoms at the interface. We also find that the in-plane Fe–F coupling gives a positive contribution to the MAE while the in-plane Fe–O coupling gives a negative contribution. The results are useful for designing of high-PMA materials. • Perpendicular magnetic anisotropy (PMA) is a key property of MRAM. • The enhancement of PMA by inserting a LiF layer at an Fe/MgO interface is studied. • The origin of the enhancement is the suppression of mixing of Fe and O atoms. [ABSTRACT FROM AUTHOR]

In this work, we have studied the spin torque based magnetization oscillations and switching in presence of Rashba–Zeeman (RZ), Ruderman–Kittel–Kasuya–Yosida (RKKY) and Dzyaloshinskii–Moriya (DM) interactions in a double-barrier RZ | Heavy Metal (HM) | RZ magnetic tunnel junction (MTJ). The system has stable magnetization oscillations and can work as an oscillator or a switcher for a significant difference in the strength of RKKY and DM interaction under suitable spin transfer torque (STT). For the proposed system with same order of RKKY and DM interaction, a nonlinear characteristic of the magnetization oscillation is observed. However, this nonlinearity of oscillations can be reduced by an external magnetic field or considering a material with suitable RZ interaction. In addition to this, our study reveals the magnetization switching can be tuned by using suitable STT. A dependence of switching time on layer thickness is also observed. Also, the switching speed increases with the thickness for systems having either same order of RKKY and DM interaction or dominated by RKKY interaction. An opposite characteristic is seen when DM interaction dominates over RKKY interaction. • A double interface Rashba–Zeeman Magnetic tunnel junction (MTJ) can work as a magnetization switcher or a spin torque oscillator. • Rashba–Zeeman (RZ), Ruderman–Kittel–Kasuya–Yosida (RKKY) and Dzyaloshinskii–Moriya (DM) interactions play a significant role in spin torque based magnetization dynamics. • Signature of nonlinear magnetization oscillation are observed for the proposed system with same order of RKKY and DM interaction. • The magnetization switching can be tuned by using suitable STT. • Switching speed depends on thickness of RZ-layers. It increases with the increase in thickness for systems having either same order of RKKY and DM interaction or strong RKKY interaction. [ABSTRACT FROM AUTHOR]

We have studied the tunnel magneto-Seebeck (TMS) effect in magnetic tunnel junctions with a single-crystal barrier using an extending spintronic theory developed previously by us. The theory is founded on optical methods, and thus, compared to the conventional theories, it can better take into account the periodicity of the single-crystal barrier and the coherence of the tunneling process. The results show that, the Seebeck coefficients can oscillate with the barrier thickness. Physically, the oscillations come from the diffraction of the tunneling electrons by the periodic potential of the single-crystal barrier. Owing to the oscillations, there appear a series of peaks of the TMS ratio for some barrier thicknesses which correspond to the zero points of the Seebeck coefficients. In particular, the magnitudes of the calculated Seebeck coefficients are in accordance with the experimental values of the intrinsic Joule heating. Furthermore, the influences of the ferromagnetic electrodes and barrier on the oscillations are investigated. It is found that, the ferromagnetic electrodes only have a remarkable influence on the amplitudes of the oscillations, whereas the barrier has significant influences on both the amplitudes and periods. • The Seebeck coefficients can oscillate with the barrier thickness. • The diffraction of the electrons by the barrier accounts for the oscillations. • The calculated Seebeck coefficients are in accordance with the experiments. [ABSTRACT FROM AUTHOR]

We present an approach for minimizing the critical current for the magnetization switching in magnetic tunnel junctions by optimizing the spatial distribution of the current density. We show that such a minimization is possible because critical current is determined by the condition of making one of the magnetization eigenstates grow in time. The excitation of the eigenstates is enhanced when the spatial distributions of the eigenstates and current density overlap. Critical current can be viewed as a functional of the current density spatial distribution and it can be minimized by optimizing this distribution. Such an optimization results in a major reduction of the critical current and increase of the switching efficiency, viz. the ratio between the energy barrier and critical current. The minimized critical current increases approximately linearly with the magnetic tunnel junction size, which is much slower than critical current for the case of a uniform current density. The optimized efficiency can be approximately a constant with respect to the magnetic tunnel junction size, which is much higher than the efficiency for the uniform current density. Additional optimization can be achieved by spatially modulating the material parameters, e.g., the saturation magnetization. The presented approach and obtained scaling of the critical current and efficiency offers opportunities for the magnetic tunnel junction optimization. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junction (MTJ) research has been focused on MgO-based crystalline structures due to high tunnel magnetoresistance (TMR), despite requiring a more severe process control than previous generations of MTJ stacks based on amorphous barriers (e.g. AlOx). In this work, we study the electrical transport properties in AlOx barriers in MTJ sensors fabricated using Ion beam sputtering and remote plasma oxidation. Amorphous barriers were prepared from oxidation of thin Al films, deposited in single step barrier (SSB-Al 1 nm/oxidation) or double step barrier (DSB-Al 0.5 nm/oxidation/Al 0.5 nm/oxidation) structures. We show tunable resistance-area products (RxA) ranging from ≈ 10 Ω μ m 2 (suited for nano devices) up to ≈ 100 k Ω μ m 2 (suited for large area sensors) with TMR above 30%. For all geometries studied, the structures have a coercivity free linear response and require none or one annealing step. This makes them very competitive for all industrial applications where the TMR level is not the dominant specification to meet. [ABSTRACT FROM AUTHOR]

We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching. [ABSTRACT FROM AUTHOR]

Within the framework of the free-electron model, the tunneling magnetoresistance (TMR) in FM/I/SF/NM quasi-magnetic tunnel junctions (QMTJ) is investigated. FM, NM, I and SF represent the ferromagnetic metal, nonmagnetic metal, insulator and spin-filter barrier, respectively. Our results show that due to the spin-filtering effect in SF potential barriers, the FM/I/SF/NM can obtain relatively stabilized TMR in higher bias region when it has higher potential height and thicker SF barrier. And, for obtaining large TMR, the total thickness of the barrier region would be carefully selected as the influence of the supplementary I layer. [ABSTRACT FROM AUTHOR]

We present experimental data of the precessional dynamics of the free layer of CoFeB/MgO/CoFeB based magnetic tunnel junctions (MTJ) in the presence of thermal gradients across the MTJ. The free layer precession is investigated by noise spectroscopy. Thermal gradients of the order of tens of mK/nm across the MTJ are generated by electrical heating. Without applied thermal gradients we find spin transfer torque modified magnetization precession. With increasing thermal gradients we generally observe a decrease of the precession frequency which could be related to an increasing overall free layer temperature. However an asymmetry of the line width behavior for parallel and antiparallel orientation points towards additional effects beyond thermal activation. This could be a hint for the modification of the precessional dynamics in magnetic tunnel junctions by thermal spin torques. [ABSTRACT FROM AUTHOR]

Frequency modulation is performed on a vortex oscillator at various modulation frequencies and powers. A global analysis of the whole set of data is proposed, so that all experimental curves are described with the same four parameters. Three of these parameters describe the dependence of the instantaneous frequency with modulating current. This dependence appears significantly different from the frequency-current dependence observed in a quasi-static experiment. The discrepancy is ascribed to the different time scales involved, compared to the relaxation time of the vortex oscillator. [ABSTRACT FROM AUTHOR]