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We present a theoretical investigation of the magnetisation reversal process in CoFeB-based magnetic tunnel junctions (MTJs). We perform atomistic spin simulations of magnetisation dynamics induced by combination of spin orbit torque (SOT) and spin transfer torque (STT). Within the model the effect of SOT is introduced as a Slonczewski formalism, whereas the effect of STT is included via a spin accumulation model. We investigate a system of CoFeB/MgO/CoFeB coupled with a heavy metal layer where the charge current is injected into the plane of the heavy metal meanwhile the other charge current flows perpendicular into the MTJ structure. Our results reveal that SOT can assist the precessional switching induced by spin polarised current within a certain range of injected current densities yielding an efficient and fast reversal on the sub-nanosecond timescale. The combination of STT and SOT gives a promising pathway to improve high performance CoFeB-based devices with high speed and low power consumption.

We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX 2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS 2 , VSe 2 , and VTe 2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0  μ B . The GGA plus on-site Coulomb interaction U (GGA +  U ) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS 2 , VSe 2 , and VTe 2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS 2 , VSe 2 , and VTe 2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature T C , and the in-plane magnetic anisotropy together in a single layer VX 2 , this newtype 2D magnetic semiconductor shows great potential in future spintronics.

In this study, we investigate the effect of temperature on the performance of a read sensor by utilizing an atomistic model coupled with a spin transport model. Specifically, we study the temperature dependence of spin transport behavior and MR outputs in a Co 2 FeAl 0.5 Si 0.5 (CFAS)(5nm)/Cu(5nm)/CFAS(5nm) trilayer with diffusive interfaces. Initially, the two-channel model of spin-dependent resistivity is used to calculate the temperature dependence of spin transport parameters which serves as essential input for the spin accumulation model. Our findings demonstrate that as the temperature increases, the spin transport parameters and magnetic properties decrease due to the influence of thermal fluctuation. At a critical temperature, where the ferromagnet transitions to a paramagnetic state, we observe zero spin polarization. Furthermore, at elevated temperatures, the spin accumulation deviates from the equilibrium value, leading to a reduction in the magnitude of spin current and spin transport parameters due to thermal effects. As a consequence, the MR ratio decreases from 65% to 20% with increasing temperature from 0 to 400 K. Our results are consistent with previous experimental measurements. This study allows to deeply understand the physical mechanism in the reader stack which can significantly benefit reader design.

Heat assisted magnetic recording (HAMR) technology is considered a solution to overcome the limitations of perpendicular magnetic recording and enable higher storage densities. To improve and understand the performance of magnetic writers in HAMR technology, it is crucial to possess a comprehensive understanding of both the magnetic field generated during the writing process and the thermal effects induced by the laser. In this work, we have developed a micromagnetic HAMR model with atomistic parameterization. To demonstrate the applicability of the developed model, it is employed to investigate the Write Current Assisted Percentage (WCAP) measurement which is characterized by the difference in laser current needed to erase a narrow data track with and without assistance of the magnetic field generated by the writer. This value allows us to subsequently consider the strength of the magnetic field from the writer, which is difficult to evaluate experimentally. We study the effect of crucial factors such as the laser current, the frequency of the writing field and the grain size distribution of the recording media on the WCAP. The results reveal that, under a high applied field, a correspondingly elevated WCAP is generated. This observation suggests that the track undergoes erasure to approximately half of its amplitude, achieved through the utilization of a low peak temperature. The comparison between simulation and experimental data demonstrates excellent agreement and acts as a validation of the underlying principle of WCAP. Additionally, we explore theoretically the impact of the writer frequency, and the results suggest that lower frequencies give rise to an increase in WCAP. This implies that lower frequencies allow for a reduction in temperature required to erase the track. The technique is valuable in evaluating and contrasting the magnetic behavior of various write pole configurations, examining the frequency responses of different designs, and comparing different media.

Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength.

An antiferromagnet emits spin currents when time-reversal symmetry is broken. This is typically achieved by applying an external magnetic field below and above the spin-flop transition or by optical pumping. In this work we apply optical pump-THz emission spectroscopy to study picosecond spin pumping from metallic FeRh as a function of temperature. Intriguingly we find that in the low-temperature antiferromagnetic phase the laser pulse induces a large and coherent spin pumping, while not crossing into the ferromagnetic phase. With temperature and magnetic field dependent measurements combined with atomistic spin dynamics simulations we show that the antiferromagnetic spin-lattice is destabilised by the combined action of optical pumping and picosecond spin-biasing by the conduction electron population, which results in spin accumulation. We propose that the amplitude of the effect is inherent to the nature of FeRh, particularly the Rh atoms and their high spin susceptibility. We believe that the principles shown here could be used to produce more effective spin current emitters. Our results also corroborate the work of others showing that the magnetic phase transition begins on a very fast picosecond timescale, but this timescale is often hidden by measurements which are confounded by the slower domain dynamics. The authors measure picosecond spin pumping in FeRh as a function of temperature by optical pump-THz emission spectroscopy. In the antiferromagnetic phase of FeRh enhanced spin pumping above the value measured in the ferromagnetic phase is observed.

The discovery of magnetization switching via spin transfer torque (STT) in PMA-based MTJs has led to the development of next-generation magnetic memory technology with high operating speed, low power consumption and high scalability. In this work, we theoretically investigate the influence of finite size and temperature on the mechanism of magnetization switching in CoFeB–MgO based MTJ to get better understanding of STT-MRAM fundamentals and design. An atomistic model coupled with simultaneous solution of the spin accumulation is employed. The results reveal that the incoherent switching process in MTJ strongly depends on the system size and temperature. At 0 K, the coherent switching mode can only be observed in MTJs with the diameter less than 20 nm. However, at any finite temperature, incoherent magnetization switching is thermally excited. Furthermore, increasing temperature results in decreasing switching time of the magnetization. We conclude that temperature dependent properties and thermally driven reversal are important considerations for the design and development of advanced MRAM systems.

The study of laser-induced ultrafast magnetization dynamics is crucial for the development of information recording technology. Due to the complex mechanism, there is still a lack of comprehensive understanding for ultrafast magnetization dynamics. As an essential stage of laser-induced ultrafast magnetization switching process, the transient ferromagnetic like state (TFLS), has attracted much attention. Different from other studies on TFLS through the difference of magnetization dynamics between rare-earth and transition-metal, our study mainly focuses on the influence of energy injection and relaxation on TFLS in the process of ultrafast magnetization dynamics. The influence of various parameters on the formation of energy exchange dependent TFLS is studied. The results of simulation well support our view. Understanding the mechanism behind the TFLS is of great significance to promote the application of laser-induced ultrafast magnetization switching.

Power consumption is the main limitation in the development of new high performance random access memory for portable electronic devices. Magnetic RAM (MRAM) with CoFeB/MgO based magnetic tunnel junctions (MTJs) is a promising candidate for reducing the power consumption given its non-volatile nature while achieving high performance. The dynamic properties and switching mechanisms of MTJs are critical to understanding device operation and to enable scaling of devices below 30 nm in diameter. Here we show that the magnetic reversal mechanism is incoherent and that the switching is thermally nucleated at device operating temperatures. Moreover, we find an intrinsic thermal switching field distribution arising on the sub-nanosecond time-scale even in the absence of size and anisotropy distributions or material defects. These features represent the characteristic signature of the dynamic properties in MTJs and give an intrinsic limit to reversal reliability in small magnetic nanodevices.

A magnetic bimeron is an in-plane topological counterpart of a magnetic skyrmion. Despite the topological equivalence, their statics and dynamics could be distinct, making them attractive from the perspectives of both physics and spintronic applications. In this work, we demonstrate the stabilization of bimeron solitons and clusters in the antiferromagnetic (AFM) thin film with interfacial Dzyaloshinskii–Moriya interaction (DMI). Bimerons demonstrate high current-driven mobility as generic AFM solitons, while featuring anisotropic and relativistic dynamics excited by currents with in-plane and out-of-plane polarizations, respectively. Moreover, these spin textures can absorb other bimeron solitons or clusters along the translational direction to acquire a wide range of Néel topological numbers. The clustering involves the rearrangement of topological structures, and gives rise to remarkable changes in static and dynamical properties. The merits of AFM bimeron clusters reveal a potential path to unify multibit data creation, transmission, storage, and even topology-based computation within the same material system, and may stimulate spintronic devices enabling innovative paradigms of data manipulations.