Heat-assisted magnetic recording (HAMR) and heated dot magnetic recording (HDMR) technologies are promising data storage solutions proposed to increase the areal density (AD) beyond 4 [Formula: see text]. However, there is a possibility of "back-switching" of the recorded data due to the thermally induced fluctuations at the elevated recording temperature, which can lead to an increased bit error rate (BER) in HAMR/HDMR. In this work, we investigate the effects of crucial parameters such as writing time, writing field, and damping constant on writing performance, particularly in relation to AD and BER. The atomistic spin model, implemented via the VAMPIRE software package, is employed to analyze the dynamics of the magnetization switching process, enabling the calculation of BER. We also propose a master equation model for calculating magnetization cooling curves that aligns with numerical simulations. Our results show that magnetic grains with a diameter of 5 nm are suitable for increasing areal density, achieving an AD of 16.4 [Formula: see text]. However, smaller grains with diameters of 3 nm and 4 nm, although providing a higher areal density than the 5 nm grains, exhibit a higher BER. Interestingly, for the system with high AD the BER can be reduced by applying a higher writing field and longer writing time or selecting a storage medium with high damping constant. This study demonstrates how to optimize key factors to enhance the writing performance in HAMR and HDMR technologies.

We have developed a model of a CoFeB/MgO magnetic tunnel junction nano-pillar for application as a spin torque nano-oscillator (MTJ-STNO) using an atomistic model combined with a spin accumulation model. We investigate the effect of current density on magnetization dynamic states and the impact of the precession angle between magnetizations in the free layer and the pinned layer on the performance of the MTJ-STNO. An optimal current density is found where the relatively narrow linewidth within the simulation framework. Here, the magnetization rotates with a resonant frequency in the GHz range, reaching the steady precessional state within 1 ns. This behavior is caused by the balance between the Gilbert damping torque and the adiabatic spin torque in the free layer. The optimal current density decreases as the precession angle increases, because the spin torque acting on the magnetization in the free layer increases. As a result, the resonant frequency decreases (from 22.56 to 11.02 GHz) and power consumption decreases to the mu W level, while the amplitude increases. This study is an important milestone toward the application of STNO for the next-generation data and communication technologies such as wireless communication, microwave assisted magnetic recording (MAMR), and neuromorphic computing.

After 20 years of development, heat-assisted magnetic recording (HAMR) is now entering production. Given the timescale associated with HAMR development, it seems important to consider the possibilities for future replacement. HAMR is limited by the phenomenon of "backswitching" which, in the limited write fields available to the HAMR process, leads to a reduction of switching probability: a reduction which becomes more pronounced as the grain size continues to decrease. An interesting possibility for technology beyond HAMR is all-optical switching (AOS), which is a field-free option thereby removing the need for an inductively generated head field. Since the AOS is driven by exchange, the effective fields involved are extremely large and the backswitching is dramatically reduced leading to more reliable switching. We review the underlying physics of the backswitching in terms of a "quadrilemma" and show how this is overcome by AOS. We also outline recent processes designed to switch ferromagnets and the usage of combined AOS/spin torque to achieve deterministic rather than the toggle switching exhibited by ferrimagnets. The conclusion is that any materials' design must ensure a sufficiently large effective field to overcome backswitching.

We theoretically investigate the spin transport behavior of multilayer (Co2FeSi/Ag)N structure for the application of next-generation read sensors in hard disk drive. To demonstrate the potential of the Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device, we employ an atomistic model coupled with a spin accumulation model including the effect of a diffuse interface. The dynamics of magnetization is observed in the atomistic model and the calculation of magnetoresistance (MR) and MR ratio of the magnetic structure can be achieved by the spin accumulation model enabling us to investigate the spin transport behavior within the structure. The MR value can be directly calculated from the gradient of spin accumulation and spin current. The effect of injected current density is first investigated. It is found that increasing the current density results in a high MR ratio. Subsequently, to achieve a high performance reader, the number of coupled layers (N) is varied up to 16 to study its effect on the MR ratio. The calculated results indicate that increasing the number of layers N gives rise to the enhancement of the resistance change and MR ratio. At the critical point N = 5, further increasing N does not affect the MR ratio, which remains relatively unchanged. Interestingly, the MR ratio is doubled for N>5 compared to N = 1. Our results demonstrate the possibility of enhancing the performance of multilayer CPP-GMR devices.

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.

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

Heat assisted magnetic recording (HAMR) is a novel high-density magnetic recording technology that relies on thermal assist from a laser during the writing process. To achieve high writing performance, it is important to study and optimize the crucial factors affecting the magnetization reversal mechanism at elevated temperature. In this work, we use a multiscale approach that combines atomistic and micromagnetic models to study the magnetization reversal behavior in the recording medium. The atomistic model allows to parameterize accurately the macroscopic approach, which is utilized to model the system and its dynamics. We perform a parametric investigation of the switching properties as a function of the HAMR setup characteristics as well as the material properties, such as magnetic damping. The results show that high damping and moderate external fields can achieve high-performance HAMR media characterized by high switching probability, short switching time and low peak temperature. We demonstrate that switching occurs via the linear reversal mechanism. By systematic variation of the longitudinal susceptibility we force a transition to coherent reversal and demonstrate that this reduces the switching probability, showing linear reversal to be an important component within the HAMR process.

In this work, we theoretically investigate the size dependence of the magnetization reversal behavior in CoFeB-MgO-CoFeB magnetic tunnel junctions (MTJs) by employing an atomistic spin model coupled with the spin accumulation model. The former and the latter are used to construct the magnetic structure and to model the spin transport behavior, respectively. The accuracy of the approach is confirmed by investigating the dependence of the magnetic properties on the size of the MTJ. Perpendicular magnetic anisotropy (PMA) is observed for thickness less than 1.3 nm, which is in an excellent agreement with experiment. To investigate the magnetization dynamics induced by spin-polarized current, a charge current is injected into the MTJ structure perpendicular to the stack leading to a spin-transfer torque acting on the magnetization of the CoFeB layer. The results show that the critical current density to reverse the magnetization is lower for PMA-MTJ and in addition for the same injected current density the time required to switch the magnetization is shorter than for an in-plane MTJ. The results can be used as a guideline to optimize the design of high performance MTJs for STT-MRAM applications.

Heusler alloy has been widely utilized in magnetoresistive sensors to enhance the device performance. In this work, we theoretically investigate the performance of Heusler-alloy-based magnetoresistive sensors with a synthetic antiferromagnet (SAF) layer. The atomistic model combined with the spin accumulation model will be used in this work. The former is used to construct the reader stack and investigate the magnetization dynamics in the system. The latter is employed to describe the spin transport behavior at any position of the structure. We first perform simulations of the exchange bias (EB) phenomenon in the IrMn/ Co2FeSi (CFS) system providing a high EB field. Then, a realistic reader stack of IrMn/CFS/Ru/CFS/Ag/CFS is constructed via an atomistic model. Subsequently, the resistance-area product (RA) and magnetoresistance (MR) ratio of the reader can be calculated by using the spin accumulation model. As a result of the spin transport behavior in the Heusler-alloy-based reader stack including SAF structure at 0 K, an enhancement of the MR ratio up to 120 % and RA <40m Omega & sdot;mu m(2) can be observed. This study demonstrates the important role of the Heusler alloy and SAF layer in the development of magnetoresistive sensors for the application of readers in hard disk drives with an areal density beyond 2 Tb in(-2).

An exchange bias (EB) model taking the setting process into account is developed to study the effect of the crucial parameters, such as the AFM anisotropy constant (KAF), the setting temperature (Tset), and the physical microstructure on the exchange bias field of an AFM/FM system. The magnetization dynamics of the EB system is treated using the kinetic Monte Carlo approach and by integrating the Landau–Lifshitz–Gilbert equation for AFM and FM layers, respectively. We first investigate the variation of the exchange bias field (HEB) as a function of KAF in the IrMn/CoFe system. It is found that HEB strongly depends on the energy barrier dispersion determined by dispersions of KAF and the grain volume. It is shown that the HEB is affected by the physical microstructure of the IrMn layer: film thickness and grain diameter. We also demonstrate that the maximum setting fraction (fset) related to HEB can be achieved by optimizing the value of KAF and Tset. The simulation results of the setting process are in good agreement with previous experimental works. This confirms the validity of the EB model, including the setting process that can be used as a powerful tool for the application of spintronics, especially for read sensor design to achieve high thermal stability with scaling down of components.

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.

We develop a code to extract the signal-to-noise ratio (SNR) arising from the magnetic film in a recording medium. The approach allows us to separate the remanence and transition contributions from the global spatial noise. The results are in excellent agreement with the analysis performed on the same data sets by means of Seagate proprietary software based on ensemble wave-form analysis. We then apply this analytical approach to the results of heat-assisted magnetic recording (HAMR) dynamics simulations by means of the open-source multi-time-scale micromagnetic code MARS and compare these with experimental spin-stand measurements of analogous systems. The proposed model could be used as the standard tool to understand the underlying physics of the noise components affecting HAMR operations and how to decrease the noise arising from the medium to improve the writing performance of HAMR.

We use an atomistic spin model to simulate FePt-based bilayers for heat assisted magnetic recording (HAMR) devices and investigate the effect of various degrees intermixing that might arise throughout the fabrication, growth and annealing processes, as well as different interlayer exchange couplings, on HAMR magnetisation dynamics. Intermixing can impact the device functionality, but interestingly does not deteriorate the properties of the system. Our results suggest that modest intermixing can prove beneficial and yield an improvement in the magnetisation dynamics for HAMR processes, also relaxing the requirement for weak exchange coupling between the layers. Therefore, we propose that a certain intermixing across the interface could be engineered in the fabrication process to improve HAMR technology further.

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 investigate the dynamical switching process of Heat Assisted Magnetic Recording (HAMR) by numerical calculations of switching probability using an atomistic model. Calculations show that at the elevated write temperature of HAMR there is a loss of information arising from 'backswitching': a thermodynamic phenomenon which comes into play when the ratio of the Zeeman energy to the thermal energy is insufficiently large to completely stabilise the switched direction. We consider the special case of Heated Dot Magnetic Recording, where a reduction of switching probability can be related to a bit error rate. We show that the backswitching becomes more pronounced at faster write times. Also, we show that in the case of current recording media, based on the binary alloy FePt, backswitching will be a more stringent limitation on recording density than the usually assumed thermal stability criterion.

Micromagnetic modelling provides the ability to simulate large magnetic systems accurately without the computational cost limitation imposed by atomistic modelling. Through micromagnetic modelling it is possible to simulate systems consisting of thousands of grains over a time range of nanoseconds to years, depending upon the solver used. Here we present the creation and release of an open-source multi-timescale micromagnetic code combining three key solvers: Landau-Lifshitz-Gilbert; Landau-Lifshitz-Bloch; Kinetic Monte Carlo. This code, called MARS (Models of Advanced Recording Systems), is capable of accurately simulating the magnetisation dynamics in large and structurally complex single- and multi-layered granular systems. The short timescale simulations are achieved for systems far from and close to the Curie point via the implemented Landau-Lifshitz-Gilbert and Landau-Lifshitz-Bloch solvers respectively. This enables read/write simulations for general perpendicular magnetic recording and also state of the art heat assisted magnetic recording (HAMR). The long timescale behaviour is simulated via the Kinetic Monte Carlo solver, enabling investigations into signal-to-noise ratio and data longevity. The combination of these solvers opens up the possibility of multi-timescale simulations within a single software package. For example the entire HAMR process from initial data writing and data read back to long term data storage is possible via a single simulation using MARS. The use of atomistic parameterisation for the material input of MARS enables highly accurate material descriptions which provide a bridge between atomistic simulation and real world experimentation. Thus MARS is capable of performing simulations for all aspects of recording media research and development. This ranges from material characterisation and optimisation to system design and implementation.

We perform atomistic simulations of spin transfer torque switching dynamics in CoFeB/MgO/CoFeB magnetic tunnel junctions. We base our study on Slonczewski's model parametrized following the approach of Zhang, Levy, and Fert. We utilize excitation modes and the contour integral of the magnetization to perform a deeper analysis of the switching mechanism driven by spin transfer torque. Our results show a magnetization reversal driven by the combination of coherent and nonuniform excitation modes. These can be nonuniform and initiated by a coherent mode of the magnetization, or domain wall nucleated depending on the lateral size, temperature, and current density injected into the system. Larger current densities result in stronger excitation of nonuniform modes making the switching more easily subjected to thermal excitations and structural imperfections such as edge damage. Our findings agree with experimental works on spin transfer torque switching in similar CoFeB/MgO-based systems, and they suggest the presence of complex features in the magnetization dynamics. The analysis and the results presented here can help to gain a deeper understanding of spin transfer torque dynamics in nanoscale devices.

Increasing the data storage in next-generation hard disk drives requires a reduction in the physical dimensions of read sensors. Tunneling magnetoresistance heads yield high magnetoresistance (MR) ratio but with a high resistance-area product (RA) that is suboptimal for devices. Giant magnetoresistance (GMR) head using different materials is an alternative way to improve reader performance with high MR ratio and low RA. In this paper, we theoretically study the effect of material properties and the layer thickness on RA and MR ratio in a trilayer system via an atomistic model combined with the spin transport model. The GMR stack can be constructed by the atomistic model and the RA and MR ratio can be directly calculated by considering the spin accumulation and spin current from the spin transport model. It is found that the spin valve using the Co2FeAl Heusler alloy electrode with high spin polarization exhibits a high MR ratio and RA of 64 m Omega mu m(2) which is better than the spin valves using conventional ferromagnets such as Co, NiFe and CoFe. Moreover, we consider the thickness dependence of the change of RA (Delta RA). Increasing the free layer thickness yields the increase in Delta RA and MR ratio because of the enhancement of the bulk spin scattering. Additionally, the results show that the Delta RA depends on the spin diffusion length of the nonmagnetic materials (lambda(sdl,NM)). The Delta RA increases from 3 up to 10 m Omega mu m(2) when lambda(sdl,NM) increases from 35 to 1200 nm. This investigation shows the possibility for read head design of HDDs with areal density beyond 2 Tb in(-2).

In this work, the current-induced domain wall (DW) motion driven by spin Hall effect (SHE) is theoretically investigated via an atomistic model. The SHE is taken into account in the atomistic model as a Slonczewski torque term. We first consider a bilayer system consisting of a ferromagnetic layer (FM) adjacent to a heavy metal (HM). To study the effect of spin Hall angle and FM thickness on DW motion in perpendicularly magnetized FM, an in-plane current is injected into HM. The results show that the critical current density, DW velocity and DW displacement strongly depend on the spin Hall angle and thickness of FM. To demonstrate the efficiency of SOT, we also study the DW motion driven by spin-transfer torque (STT) in a FM/NM/FM system by injecting a charge current perpendicularly to the plane of the structure. The DW velocity and DW displacement of two cases are compared. At the same current density, it is clearly observed that the DW in the presence of SOT is more easily moved with higher velocity and DW displacement. In addition, the critical current density of SHE driven case is smaller compared with spin torque case. To move the DW with the velocity of 100 m/s, the injected current density required for the STT case could be 10 times as high as the SHE case. The proposed model can be used to optimize all factors for spintronic device design with low power consumption, fast speed and high endurance such as the DW-based devices and the perpendicularly magnetized SOT-MRAM.

The study and understanding of spin-transport mechanisms including thermal fluctuation are required for the development and design of spintronic devices. In this paper, we present an approach to investigate the temperature dependence of spin-transport behavior within the magnetic structure by using the generalized spin accumulation model. The temperature affects not only the magnetization orientation, but also the spin-transport properties. Its effect on transport parameters can be taken into account by considering the spin-dependent resistivity at any finite temperature. This leads to the calculation of temperature-dependent spin-transport parameters and eventually allows the calculation of the thermal effects on spin accumulation, spin current, and spin torque. It is observed that increasing temperature is likely to decrease the value of key transport parameters relevant to the magnitude of spin torque. This study demonstrates the importance of thermal effects on spin-transport behavior which needs to be considered for spin-transfer torque based device design with high performance.