Magnetic Random Access Memory Research Articles

Accurate Torque Evaluation in Elongated Ultra-Scaled STT-MRAM Devices

Emerging spin-transfer torque magnetoresistive random access memory (STT-MRAM) is attractive for stand-alone and embedded applications. STT-MRAM is nonvolatile, operates fast, and possesses excellent endurance. STT-MRAM is compatible with CMOS technology and can be integrated during the back-end-of-line process. This makes STT-MRAM promising for automotive and IoT applications, microcontrollers, frame buffer memory, and last level cache. The core of modern STT-MRAM cells consists of a magnetic tunnel junction (MTJ), which is a sandwich of two ferromagnetic (FM) layers separated by a tunnel barrier (TB). The FM layers are referred to as reference layer (RL) and free layer (FL). The magnetization of the RL is fixed, while the magnetization of the FL can be reversed. The use of MTJs with perpendicular magnetic anisotropy (PMA) permits to obtain better scalability and lower switching currents. When the magnetization vectors of the FL and RL are parallel (P), the electrical resistance is lower than when the vectors are anti-parallel (AP), which provides a way to store binary information. Importantly, the switching between these two stable configurations is achieved by purely electrical means.To reduce the footprint and benefit from shape-induced anisotropy, an ultra-scaled MRAM cell with a composite FL made of several elongated ferromagnetic pieces, separated by multiple MgO barriers, was proposed and demonstrated [1]. In elongated FLs, shown in Fig.1a, domain walls or magnetization textures can be generated during switching. In this case, additional spin torques created by the presence of magnetization gradients inside the ferromagnetic parts must be considered. This type of torque is typically modeled by the Zhang-Li expression [2]. If the spin dephasing length correctly describes the coupled charge and spin transport through the device, the expression for bulk torque must be generalized [3].In MTJs, however, there exists another torque acting on a FL close to the interface with MgO. This torque, predicted by Slonczewski [4] and Berger [5], was utilized to flip the magnetization in traditional MTJs with a FL fabricated as a flat and thin disk. It is due to the spin-polarized current coming across the TB from the RL. Electrons tunneling from the RL become spin-polarized. When entering the FL, the spin polarized electrons interact with the magnetization via the exchange interaction. When the magnetization vectors in the RL and FL are not aligned, the spin current components normal to the FL magnetization are quickly absorbed. Due to conservation of the angular momentum, the absorption of the normal component of the spin current results in a torque acting on the FL magnetization in the opposite sense. If the current is sufficiently strong, the magnetization of the FL can be switched between the two stable P and AP configurations relative to the RL.As the Slonczewski torque is localized at the interface and Zhang-Li (ZL) torque is acting in the bulk, the two torques are usually assumed to be independent. However, this is not correct [5]. Although the spin component normal to the FL magnetization is indeed quickly absorbed, the interface-polarization induced spin current parallel to the magnetization propagates into the FL at a longer distance determined by the spin-flipping length. This length is about 10nm in typical FL materials. As the interface-polarization induced spin current hits the spin texture, it modifies the ZL torque value determined by the spin polarization in the bulk. The FL in ultra-scaled MRAM cells contains a TB on both interfaces. Here, we compare the ZL torque acting on the domain wall (Fig.1b) for the case, when the interface polarization at the second TB is lower than the spin polarization in the bulk (Fig.1c) or higher (Fig.1d). It is demonstrated that the torque acting on the domain wall can be enhanced compared to the ZL value for the case of larger interface polarization than spin polarization in the bulk. B. Jinnai, J. Igarashi, K. Watanabe et al. High-performance shape-anisotropy magnetic tunnel junctions down to 2.3 nm, in Proc. IEDM Conf., 2020, pp. 24.6.1-24.6.4, doi: 10.1109/IEDM13553.2020.9371972S. Zhang and Z. Li. Roles of nonequilibrium conduction electrons on the magnetization dynamics of ferromagnets. Phys. Rev. Lett., vol. 93, 127204, 2004 doi: 10.1103/PhysRevLett.93.127204J. C. Slonczewski. Current-driven excitation of magnetic multilayers, J. Magn.Magn. Mater., vol. 159, no. 1, pp. L1 - L7, 1996, doi: 10.1016/0304-8853(96)00062-5L. Berger. Emission of spin waves by a magnetic multilayer traversed by a current, Phys. Rev. B, vol. 54, pp. 9353-9358, 1996, doi: 10.1103/PhysRevB.54.9353S. Fiorentini, M. Bendra, J. Ender et al. Spin and charge drift-diffusion in ultra-scaled MRAM cells, Sci. Rep., vol. 12, 20958, pp.1-13, 2022, doi: 10.1038/s41598-022-25586-4 Figure 1

A Comprehensive Study of Temperature and Its Effects in SOT-MRAM Devices.

We employ a fully three-dimensional model coupling magnetization, charge, spin, and temperature dynamics to study temperature effects in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). SOTs are included by considering spin currents generated through the spin Hall effect. We scale the magnetization parameters with the temperature. Numerical experiments show several time scales for temperature dynamics. The relatively slow temperature increase, after a rapid initial temperature rise, introduces an incubation time to the switching. Such a behavior cannot be reproduced with a constant temperature model. Furthermore, the critical SOT switching voltage is significantly reduced by the increased temperature. We demonstrate this phenomenon for switching of field-free SOT-MRAM. In addition, with an external-field-assisted switching, the critical SOT voltage shows a parabolic decrease with respect to the voltage applied across the magnetic tunnel junction (MTJ) of the SOT-MRAM cell, in agreement with recent experimental data.

Progress and Application Perspectives of Voltage‐Controlled Magnetic Tunnel Junctions

AbstractThis article discusses the current state of development, open research opportunities, and application perspectives of electric‐field‐controlled magnetic tunnel junctions that use the voltage‐controlled magnetic anisotropy effect to control their magnetization. The integration of embedded magnetic random‐access memory (MRAM) into mainstream semiconductor foundry manufacturing opens new possibilities for the development of energy‐efficient, high‐performance, and intelligent computing systems. The current generation of MRAM, which uses the current‐controlled spin‐transfer torque (STT) effect to write information, has gained traction due to its nonvolatile data retention and lower integration cost compared to embedded Flash. However, scaling MRAM to high bit densities will likely require a transition from current‐controlled to voltage‐controlled operation. In this perspective, an overview of voltage‐controlled magnetic anisotropy (VCMA) as a promising beyond‐STT write mechanism for MRAM devices is provided and recent advancements in developing VCMA‐MRAM devices with perpendicular magnetization are highlighted. Starting from the fundamental mechanisms, the key remaining challenges of VCMA‐MRAM, such as increasing the VCMA coefficient, controlling the write error rate, and achieving field‐free VCMA switching are discussed. Then potential solutions are discussed and open research questions are highlighted. Lastly, prospective applications of voltage‐controlled magnetic tunnel junctions (VC‐MTJs) in security applications, extending beyond their traditional role as memory devices are explored.

High room temperature magnetoresistance in La0.9Sr0.1Mn1-yZnyO3 epitaxial films

Developing large room temperature magnetoresistance materials has been a major hotspot for a few last decades due to its importance in the practical applications in magneto-resistive random access memory, and it remains a challenge. Here, La0.9Sr0.1Mn1-yZnyO3 (LSMZO) films have been grown on SrTiO3 substrates by magnetron sputtering, showing excellent quality of epitaxy. Upon increasing Zn content, the reduction of Curie temperature (TC) and metal-insulator transition temperature (TMI) is observed, accompanied by the increase of coercive field and room-temperature resistivity. Analysis on the fraction of Mn3+ and Mn4+ indicates that Zn2+ substitution at Mn site results in a higher Mn4+ fraction departing from the optimum value and hence a weaker double-exchange interaction by replacing more Mn3+. Besides that, ionic radius mismatch induced internal strain and substrate induced tensile strain also play a part. Most significantly, the enhanced magnetic disorder gives rise to an increase of intrinsic magnetoresistance around room temperature in LSMZO (y = 10%) film, and a large magnetoresistance of 18.4% is obtained under 0.3 T at 280 K in this sample. Our research provides a simple and effective approach to achieve a large room temperature magnetoresistance in Mn site doped manganite epitaxial films.

MRAM Devices to Design Ternary Addressable Physically Unclonable Functions

We introduce a novel approach to constructing ternary addressable physically unclonable functions (TAPUFs) using magnetoresistive random-access memory (MRAM) devices. TAPUFs use three states (1, 0, and X) to track unstable cells. The proposed TAPUF leverages the resistance properties of MRAM cells to produce unique digital fingerprints that can be effectively utilized in cryptographic protocols. We exploit the cell-to-cell variations in resistance values to generate reliable cryptographic keys and true random numbers, which can add protection against certain attacks. To evaluate the performance of the TAPUF, various tests were conducted, including assessments of inter-cell to intra-cell variation, inter-distance, bit error rate (BER), and temperature variation. These experiments were conducted using a low-power client device to replicate practical scenarios. The obtained results demonstrate that the proposed TAPUF exhibits exceptional scalability, energy efficiency, and reliability.

TinyVers: A Tiny Versatile System-on-Chip With State-Retentive eMRAM for ML Inference at the Extreme Edge

Extreme edge devices or Internet-of-Things (IoT) nodes require both ultra-low power (ULP) always-on (AON) processing as well as the ability to do on-demand sampling and processing. Moreover, support for IoT applications, such as voice recognition, machine monitoring, and so on, requires the ability to execute a wide range of machine learning (ML) workloads. This brings challenges in hardware (HW) design to build flexible processors operating in ULP regime. This article presents TinyVers, a tiny versatile ULP ML system-on-chip (SoC) to enable enhanced intelligence at the extreme edge. TinyVers exploits dataflow reconfiguration to enable multi-modal support and aggressive on-chip power management for duty cycling to enable smart sensing applications. The SoC combines an reduced instruction set computer-V (RISC-V) host processor, a 17-tera operations per second per watt (TOPS/W) dataflow reconfigurable ML accelerator, a 1.7- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W deep sleep wake-up controller (WuC), and an embedded magnetoresistive random access memory (eMRAM) for boot code and ML parameter retention. The SoC can perform up to 17.6 giga operations per second (GOPS) while achieving a power consumption range from 1.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W to 20 mW. Multiple ML workloads aimed for diverse applications are mapped on the SoC to showcase its flexibility and efficiency. All the models achieve 1–2 TOPS/W of energy efficiency with a power consumption below 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W in continuous operation. In a duty-cycling use case for machine monitoring, this power is reduced to below 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> W.

Proximity-Induced Tunable Magnetic Order at the Interface of All-van der Waals-Layered Heterostructures.

Spin-orbit coupling (SOC) plays a crucial role in controlling the spin-charge conversion efficiency, spin torque, and complex magnetic spin structures. In this study, we investigate the interplay between SOC and ferromagnetism in heterostructures of large-SOC and magnetic materials. We highlight the importance of the SOC-proximity effect on magnetic ordering in all-van der Waals-layered heterostructures, specifically Fe3GeTe2(FGT)/monolayer W1-xVxSe2 (x = 0 and 0.05). By increasing the SOC strength, we demonstrate various magnetic orderings induced at the interface of the heterostructure, including spin-flop, spin-flip, and inverted magnetization. Moreover, we show a sharp magnetic switching from antiferromagnetic state to ferromagnetic state in FGT/W0.95V0.05Se2, which is characteristic of the synthetic antiferromagnetic structure. This proof-of-concept result offers the possibility of interface-tailoring spintronics, including two-dimensional magnetoresistive random access memory toggle switching. Our findings provide insight into the design and development of next-generation spintronic devices by exploiting the interplay between SOC and magnetic ordering in all-van der Waals-layered heterostructures.

Nocturnal Turbulence at Jezero Crater as Determined From MEDA Measurements and Modeling

AbstractMars 2020 Mars Environmental Dynamics Analyzer (MEDA) instrument data acquired during half of a Martian year (Ls 13°–180°), and modeling efforts with the Mars Regional Atmospheric Modeling System (MRAMS) and the Mars Climate Database (MCD) enable the study of the seasonal evolution and variability of nocturnal atmospheric turbulence at Jezero crater. Nighttime conditions in Mars's Planetary Boundary Layer are highly stable because of strong radiative cooling that efficiently inhibits convection. However, MEDA nighttime observations of simultaneous rapid fluctuations in horizontal wind speed and air temperatures suggest the development of nighttime turbulence in Jezero crater. Mesoscale modeling with MRAMS also shows a similar pattern and enables us to investigate the origins of this turbulence and the mechanisms at play. As opposed to Gale crater, less evidence of turbulence from breaking mountain wave activity was found in Jezero during the period studied with MRAMS. On the contrary, the model suggests that nighttime turbulence at Jezero crater is explained by increasingly strong wind shear produced by the development of an atmospheric bore‐like disturbance at the nocturnal inversion interface. These atmospheric bores are produced by downslope winds from the west rim undercutting a strong low‐level jet aloft from ∼19:00 to 01:00 LTST and from ∼01:00 LTST to dawn when undercutting weak winds aloft. The enhanced wind shear leads to a reduction in the Richardson number and an onset of mechanical turbulence. Once the critical Richardson Number is reached (Ri ∼ &lt;0.25), shear instabilities can mix warmer air aloft down to the surface.

A high-speed and power-efficient gradient-pulse injection method for spin-transfer torque magnetic random-access memory

With the development of modern computer storage technology, the spin-transfer torque magnetic random-access memory (STT-MRAM) has become one of the most promising candidates to replace the static random-access memory and dynamic random-access memory. However, its large power consumption and long relaxation time before the magnetic moments switch are important factors restricting its commercial application. In this work, gradient-current pulses are proposed to replace the conventional constant-current pulses in the injection method. A 70-nm classical CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) with perpendicular magnetic anisotropy was simulated and measured at pulse widths of 20, 30, and 40 ns using the proposed and conventional injection pulses. The comparison results show that adopting gradient pulses can significantly reduce the relaxation time and switching power consumption of the MTJ. A power consumption reduction of 8%–40% is obtained at different pulse amplitudes and widths. Our method paves an avenue for overcoming the issues affecting the STT-MRAM and could help to promote its commercial applications.

Investigations on low temperature magnetic and magnetoelectric properties of multiferroic-NiO nanocomposites

Multiferroic BiFeO3-NiO (BFO-NiO) nanocomposites have been synthesized using sol-gel route and investigated via. the first principle DFT calculations, multiferroic-magnetoelectric response, and extremely low-temperature magnetic analysis. Powder X-ray diffraction (XRD) patterns along with Rietveld refinement data confirmed the phase purity viz. rhombohedral distorted perovskite BiFeO3- rock salt type NiO crystal structure and composite formation. Temperature dependent magnetic measurements confirmed the enhancement in the magnetism and the exchange bias effect due to the antiferromagnetic (AFM) and ferromagnetic (FM) exchange coupling interactions. Zero field cooled (ZFC) and field cooled (FC) magnetic results demonstrate the observation of typical superparamagnetic (SP) behavior for all the samples at room temperature whereas at low temperature a transition is reported from SP to quantum superparamagnetic (QSP) state through quantum tunneling of magnetic moment for all samples. Maximum polarization of 5.7μC/cm2 is observed for BFO-20% NiO composition. The noticeable change in the ferroelectric P vs E loops in the presence of external magnetic field confirm the evidence of multiferroic and magnetoelectric coupling behavior in the BFO-NiO nanocomposites. The DFT calculations have been done using WIEN2k software and found in well agreement with the reported experimental results. Further, the suitable temperature dependent magnetic squareness, evidence of considerable magnetoelectric coupling, exchange bias effect and SP nature make the BFO-NiO nanocomposites considerable suitable for various device applications such as information storage, magnetic random access memory, targeted drug delivery, magnetic resonance imaging (MRI), bio-sensing and tailoring other photocatalytic applications.

Tuning surface spin polarization of CoFeB by boron diffusion detected by spin resolved photoemission

Abstract Investigation on the spin polarization of the magnetic CoFeB thin film is of practical importance in spintronic applications. Here, using a direct characterization technique of spinresolved photoemission spectroscopy, the surface spin polarization of amorphous Co40Fe40B20 thin films with different annealing temperatures from 100 ℃ to 500 ℃ prepared by magnetron sputtering is obtained. After high annealing temperature, a quasi-semiconductor state is gradually formed at the CoFeB surface due to the boron diffusion. While the global magnetization remains almost constant, the secondary electrons’ spin polarization, average valence band spin polarization and the spin polarization at Fermi level from spin-resolved photoemission spectroscopy show a general trend of decreasing with the increasing of the annealing temperature above 100 ℃. These distinct surface properties are attributed to the enhanced Fe-B bonding due to the boron segregation upon surface after annealing as confirmed by x-ray photoelectron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy. Our findings provide insight into the surface spin-resolved electronic structure of the CoFeB thin films, which should be important for the development of high-performance magnetic random-access memory.

Ion-irradiation-induced field-free magnetization switching in synthetic antiferromagnets by spin–orbit torque

The perpendicularly magnetized synthetic antiferromagnets (SAFs) are expected to be ideal materials for magnetic random-access memory (MRAM) due to the low cross-talk noise and the high recording density. Normally, an in-plane magnetic field is required to break the inversion symmetry for deterministic magnetization switching in perpendicular SAFs by SOTs, which is undesirable for applications. In this work, the ion-irradiation method was adopted to engineer the interface of a perpendicularly magnetized Pt/Co/Pt/Ru/Pt/Co/Ta SAF to achieve the filed-free switching of the magnetization via the in-plane magnetization component of top-Co layer, which provides an in-plane effective field to bottom-Co layer and breaks the symmetry. Furthermore, with the increase of ion fluence, the critical switching current density decreases, which is consistent with the increase of spin Hall angle induced by ion-irradiation measured by the harmonic Hall voltage method. These results indicate that ion irradiation is a promising approach for realizing field-free magnetization switching in SAFs driven by SOTs and has potential application in SOT-based spintronic devices.

Neural network detector with sparse codes for spin transfer torque magnetic random access memory

Neural network detector with sparse codes for spin transfer torque magnetic random access memory

RISC-V-Based Evaluation and Strategy Exploration of MRAM Triple-Level Hybrid Cache Systems

Magnetic random access memory (MRAM) is considered one of the most promising memories among nonvolatile memories (NVMs), to replace static random access memory (SRAM) in the computing system to improve its cache performance. In this article, performance evaluation and strategy exploration of three-level hybrid cache systems are conducted under the framework of Reduced InstrucTIon Set Computer-Five (RISC-V) instruction set. First, system-level joint calls of Nvsim, Gem5, McPAT, and other cache emulation architectures are implemented based on the system-level simulator called MAGPIE tool. Based on the performance comparison of spin transfer torque (STT)-MRAM, spin-orbit torque (SOT)-MRAM, and SRAM with varied capacities, a variety of combined CPU three-level hybrid cache architectures are simulated. The performances of the proposed hybrid cache systems and the bus impact of interconnecting are evaluated, with better analysis of the cost of CPU system implementation and interactions among levels of cache. The power consumption of different processors with various instruction sets and cores is also evaluated. It is demonstrated that SOT-MRAM and STT-MRAM show great potential applications as L2 and L3 caches in the RISC-V system. RISC-V shows the potential benefits for future CPU cache. Meanwhile, an adaptive stride prefetching strategy is proposed to address the problem of delay hysteresis and high miss rate of STT-MRAM in the L3 cache. The applicability of this strategy to different storage technologies and the comparison with cutting-edge technologies are also illustrated. Simulation results show that the prefetching strategy can achieve at most 64.12% and 94.55% optimization effects on the miss latency and the miss rate of L3 cache, respectively.

Low Energy and Write-Efficient Spin-Orbit Torque-Based Triple-Level Cell MRAM

Multi-level cell (MLC) is an attractive method to increase the memory storage density and reduce the cost per bit. Write disturb rate (WDR) and large writing step counts are the main challenge to implementing MLCs. In this paper, a three-bit spin-orbit torque magnetic random-access memory (SOT-MRAM) based MLC structure named TLC is proposed. The majority of the bits in TLC require two steps of writing for storage, and the cell exhibits WDR less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> . The performance evaluation of the proposed structure is done on the SPICE framework utilizing a Verilog-A model for the structure. The proposed TLC device is 96% and 92% more energy efficient than spin transfer torque (STT) based TLC and STT/SOT-based TLC structures, respectively. The worst-case write latency of the proposed TLC is 2ns that shows 88% improvement compared to the recently published STT/SOT-based TLC-MRAM. The variability analysis performed using Monte Carlo simulations shows sufficient margins between various writing currents employed for switching the stacked magnetic tunnel junctions (MTJs) that signifies the reliable switching of the different bits in the TLC.

Low-Power and Field-Free Perpendicular Magnetic Memory Driven by Topological Insulators.

Giant spin-orbit torque (SOT) from topological insulators (TIs) has great potential for low-power SOT-driven magnetic random-access memory (SOT-MRAM). In this work, a functional 3-terminal SOT-MRAM device is demonstrated by integrating the TI [(BiSb)2 Te3 ] with perpendicular magnetic tunnel junctions (pMTJs), where the tunneling magnetoresistance is employed for the effective reading method. An ultralow switching current density of 1.5 × 105 Acm-2 is achieved in the TI-pMTJ device at room temperature, which is 1-2 orders of magnitude lower than that in conventional heavy-metals-based systems, due to the high SOT efficiency θSH = 1.16 of (BiSb)2 Te3 . Furthermore, all-electrical field-free writing is realized by the synergistic effect of a small spin-transfer torque current during the SOT. The thermal stability factor (Δ = 66) shows the high retention time (>10 years) of the TI-pMTJ device. This work sheds light to the future low-power, high-density, and high-endurance/retention magnetic memory technology based on quantum materials.

Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control

The demonstration of the charge-to-spin conversion, especially with enhanced spin Hall conductivity, is crucial for the development of energy-efficient spintronic devices such as spin–orbit torque (SOT) based magnetoresistive random access memories. In this work, fully epitaxial Ru/Cu heterostructures were fabricated with interface engineering and nanolayer insertions consisting of Cu (1 nm)/Ru (1 nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξ DL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeable ξ DL of −2.2% and the insertion of Cu/Ru nanolayers at the interface can increase the ξ DL value to −3.7%. The former could be attributed to the interface spin–orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3∼5) × 105 Ω−1 m−1 in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. This work indicates that the interfacial control with hybrid nanolayer structures can extend the SOT-based materials to highly conductive metals, even with weak spin–orbit interactions, toward high stability, low cost, and low energy consumption for spintronic applications.

Atomic scale interface engineering for realizing a perpendicularly magnetized CoFeB-based skyrmion hosting material

Néel-type magnetic skyrmions in perpendicularly magnetized systems have attracted considerable interest due to their potential in fundamental research on topological objects and spintronics applications. Various systems have been explored to study Néel-type magnetic skyrmions, including repeated magnetic multilayers, two-dimensional materials, and single magnetic thin-films. Among these, single magnetic thin-films, especially a CoFeB single layer, offers multiple benefits, such as reduced defect energy, high mobility, and easy integration with existing magnetoresistive random access memory technology. However, optimizing CoFeB-based skyrmion hosting materials remains challenging and requires further systematic and comprehensive investigation. In this study, we examine the effect of atomic-scale interface engineering by inserting a Ta layer between the CoFeB/MgO interface on perpendicular magnetic anisotropy, saturation magnetization, and Dzyaloshinskii–Moriya interaction. Moreover, we provide a guideline for engineering material parameters and demonstrate the validity of atomic-scale interface engineering. Our findings contribute to the development of optimized CoFeB-based skyrmion hosting materials.

Cubic-type Heusler compound Mn2FeGa thin film with strain-induced large perpendicular magnetic anisotropy

This study reports the development of ferrimagnetic cubic Heusler compound ${\mathrm{Mn}}_{2}{\mathrm{Fe}}_{x}\mathrm{Ga}$ (MFG) thin films with large perpendicular magnetic anisotropy (PMA). By growing MFG on a Cr buffer layer, a cubic ${\mathrm{X}}_{\mathrm{a}}$ phase with a tetragonal distortion $c/a\ensuremath{\approx}1.04$ induced by the buffer layer was obtained in the range of $x=1.0--1.3$, leading to large PMA which exceeds $0.75\phantom{\rule{4pt}{0ex}}\mathrm{MJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}3}$ in stoichiometric ${\mathrm{Mn}}_{2}\mathrm{FeGa}$ $(x=1)$. Synchrotron M\"ossbauer spectroscopy revealed that these cubic MFG thin films show good chemical ordering close to the ${\mathrm{X}}_{\mathrm{a}}$-ordered state. First-principles calculations demonstrated that, in ${\mathrm{X}}_{\mathrm{a}}$-ordered cubic MFG, the characteristic electronic structure of Fe around the Fermi level causes a large uniaxial magnetocrystalline anisotropy under the tetragonal strain consistent with experiment. The half-metallic-like band structure of cubic MFG was also shown to be preserved under the strain. Cubic ${\mathrm{Mn}}_{2}\mathrm{FeGa}$ with its small saturation magnetization, large PMA, and possibility of being highly spin polarized make this material an ideal candidate for the development of magnetic random-access memory and other spintronic devices.

Annealing effect on the magneto-electric properties of SOT-MTJs from micro to nano-sized dimensions

Spin–orbit torque magnetic random-access memory exhibits great potential for next-generation memory. Annealing is an essential process for SOT magnetic tunnel junctions (SOT-MTJs) thin films. To optimize the SOT-MTJ thin films, studying the different dimensions from micro-size to nano-size is very necessary. Here, we investigate the annealing effect on magneto-electric properties of micro-scaled and nano-scaled SOT-MTJs. The tunnel magnetoresistance (TMR) and critical current density (J c) increase after annealing, attributing to the improved crystallization of CoFeB layers and perpendicular magnetic anisotropy (PMA), respectively. However, the TMR increment of micro-scaled SOT-MTJ is larger than that in nano-scale, due to the reduced defects of micro-scaled SOT-MTJs by annealing. Additionally, the J c of nano-scaled SOT-MTJ is decoupled from that of micro-scaled SOT-MTJ because of the improved PMA and diminished thermal effect. This work assesses the different annealing effects in micro- and nano-sized dimensions and supplies experiment foundations to optimize the performance of SOT-MTJs.