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Heating magnetic nanoparticles (MNPs) with AC (Alternating Current) magnetic fields has received significant attention in recent years, particularly for biomedical uses. However, most studies focus on characterizing the heat release, overlooking the fact that the MNPs in the viscous cell environment constitute a dynamic magnetic colloid whose configuration may evolve over time, particularly if a driving force as the AC field is applied. Aiming to shed light on this matter, in this workthe dynamics of the colloid structure during hyperthermia experiments are studied. By combining various experimental and theoretical tools, it is concluded that the AC field may drive the formation of aligned structures, and the impact that such structures may have on the associated heating is assessed. Remarkably, the results show that those field‐driven structures are highly unstable for small particle sizes, rapidly disassembling upon field removal. Moreover, an analogous behavior in vitro is found, with the AC magnetic field also promoting a reversible alignment of vesicles containing the MNPs within the cells. The results suggest that the observed alignment, both of MNPs and intracellular vesicles, may be a common phenomenon in usual hyperthermia experiments, but unnoticed because of the intrinsic unstable nature of the aligned structures. [ABSTRACT FROM AUTHOR]

Ultrafast manipulation of the Néel vector in metallic antiferromagnets most commonly occurs by generation of spin-orbit (SOT) or spin-transfer (STT) torques. Here, we predict another possibility for antiferromagnetic domain switching by using novel laser optical torques (LOTs). We present results of atomistic spin dynamics simulations from the application of LOTs for all-optical switching of the Néel vector in the antiferromagnet Mn2Au. The driving mechanism takes advantage of the sizeable exchange enhancement, characteristic of antiferromagnetic dynamics, allowing for picosecond 90 and 180-degree precessional toggle switching of the Néel vector with laser fluences on the order of mJ/cm2. A special symmetry of these novel torques greatly minimises the over-shooting effect common to precessional spin switching by SOT and STT methods. We demonstrate the opportunity for LOTs to produce deterministic, non-toggle switching of single antiferromagnetic domains. Lastly, we show that even with sizeable ultrafast heating by laser in metallic systems, there exist a large interval of laser parameters where the LOT-assisted toggle and preferential switchings in magnetic grains have probabilities close to one. The proposed protocol could be used on its own for all-optical control of antiferromagnets for computing or memory storage, or in combination with other switching methods to lower energy barriers and/or to prevent over-shooting of the Néel vector. [ABSTRACT FROM AUTHOR]

Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. Here, we investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized pulses of extreme ultraviolet radiation. Our results reveal ultrafast and strong helicity-dependent magnetic effects which are in line with the characteristic fingerprints of an IFE, corroborated by ab initio opto-magnetic IFE theory and atomistic spin dynamics simulations. Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism. The authors use intense and circularly polarized pulses of extreme ultraviolet radiation to induce particularly strong effects in a ferrimagnetic GdFeCo alloy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a study of the effects of strain on the magnetocrystalline anisotropy energy and magnetic moments of Y 2 Fe 14 B bulk alloy. The study has been performed within the framework of density functional theory in its fully relativistic form under the generalized gradient approximation. We have studied seven different in-plane a lattice constant values ranging from 8.48 up to 9.08 Å with an increment of δ a = 0.1 Å. For each a value, we carried out an out-of-plane c parameter optimization, achieving the corresponding optimized lattice pair (a , c). We find a large variation in the site resolved magnetic moments for inequivalent Fe, Y, and B atoms for different lattice expansions and a negative contribution to the total moment from the Y sites. We find a strong variation in the magnetocrystalline anisotropy with the c / a ratio. However, the calculated variation when coupled with thermodynamic spin fluctuations is unable to explain the experimentally observed increase in the total magnetic anisotropy, suggesting that a different physical mechanism is likely to be responsible in contrast with previous interpretations. We show that opposing single- and two-ion anisotropy terms in the Hamiltonian gives good agreement with the experiment and is the probable origin of the non-monotonic temperature dependence of the net anisotropy of Y 2 Fe 14 B bulk alloy. [ABSTRACT FROM AUTHOR]

Using an atomistic spin model, we have simulated spin wave injection and propagation into antiferromagnetic IrMn from an exchange coupled CoFe layer. The spectral characteristics of the exited spin waves have a complex beating behavior arising from the non-collinear nature of the antiferromagnetic order. We find that the frequency response of the system depends strongly on the strength and frequency of oscillating field excitations. We also find that the strength of excited spin waves strongly decays away from the interfacial layer with a frequency dependent attenuation. Our findings suggest that spin waves generated by coupled ferromagnets are too weak to reverse IrMn in their entirety even with resonant excitation of a coupled ferromagnet. However, efficient spin wave injection into the antiferromagnet is possible due to the non-collinear nature of the IrMn spin ordering. [ABSTRACT FROM AUTHOR]

Nd 2 Fe 14 B has generated significant interest since its discovery in the 1980s due to its impressive energy density, which makes it a prime candidate for use in permanent magnet applications. Its performance is known to suffer greatly at the high temperatures required for motor applications around 450 K. Core/shell nanocomposites provide a potential route to improve material performance by combining the highly anisotropic permanent magnet with a material with high moment and high Curie temperature. We have used an atomistic spin model to investigate the magnetic properties of Nd 2 Fe 14 B with α - F e in a core/shell nanostructure. We find that at typical motor operating temperatures, increasing α - F e content reduces the coercivity of the system while enhancing the saturation magnetization. The overall effect is that an improvement in B H max is seen with increasing α - F e up to an optimal value of 70 vol. %. This property of core/shell nanostructures would make them a suitable substitute for pure Nd 2 Fe 14 B while simultaneously lowering the raw material cost of the permanent magnet component of high-performance motors. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem that standard stochastic Landau-Lifshitz-Gilbert (sLLG) simulations typically produce results that show unphysical mesh-size dependence. The root cause of this problem is that the effects of spin-wave fluctuations are ignored in sLLG. We propose to represent the effect of these fluctuations by a full-spin-wave-scaled stochastic LLG, or FUSSS LLG method. In FUSSS LLG, the intrinsic parameters of the sLLG simulations are first scaled by scaling factors that integrate out the spin-wave fluctuations up to the mesh size, and the sLLG simulation is then performed with these scaled parameters. We developed FUSSS LLG by studying the Ferromagnetic Resonance (FMR) in Nd2Fe14B cubes. The nominal scaling greatly reduced the mesh size dependence relative to sLLG. We then performed three tests and validations of our FUSSS LLG with this modified scaling. (1) We studied the same FMR but with magnetostatic fields included. (2) We simulated the total magnetization of the Nd2Fe14B cube. (3) We studied the effective, temperature- and sweeping rate-dependent coercive field of the cubes. In all three cases, we found that FUSSS LLG delivered essentially mesh-size-independent results, which tracked the theoretical expectations better than unscaled sLLG. Motivated by these successful validations, we propose that FUSSS LLG provides marked, qualitative progress towards accurate, high precision modeling of micromagnetics in hard, permanent magnets. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetic hyperthermia (MHT) is a therapeutic modality for the treatment of solid tumors that has now accumulated more than 30 years of experience. In the ongoing MHT clinical trials for the treatment of brain and prostate tumors, iron oxide nanoparticles are employed as intra-tumoral MHT agents under a patient-safe 100 kHz alternating magnetic field (AMF) applicator. Although iron oxide nanoparticles are currently approved by FDA for imaging purposes and for the treatment of anemia, magnetic nanoparticles (MNPs) designed for the efficient treatment of MHT must respond to specific physical–chemical properties in terms of magneto-energy conversion, heat dose production, surface chemistry and aggregation state. Accordingly, in the past few decades, these requirements have boosted the development of a new generation of MNPs specifically aimed for MHT. In this review, we present an overview on MNPs and their assemblies produced via different synthetic routes, focusing on which MNP features have allowed unprecedented heating efficiency levels to be achieved in MHT and highlighting nanoplatforms that prevent magnetic heat loss in the intracellular environment. Moreover, we review the advances on MNP-based nanoplatforms that embrace the concept of multimodal therapy, which aims to combine MHT with chemotherapy, radiotherapy, immunotherapy, photodynamic or phototherapy. Next, for a better control of the therapeutic temperature at the tumor, we focus on the studies that have optimized MNPs to maintain gold-standard MHT performance and are also tackling MNP imaging with the aim to quantitatively assess the amount of nanoparticles accumulated at the tumor site and regulate the MHT field conditions. To conclude, future perspectives with guidance on how to advance MHT therapy will be provided. [ABSTRACT FROM AUTHOR]

Skyrmions have attracted significant interest due to their topological spin structures and fascinating physical features. The skyrmion phase arises in materials with a Dzyaloshinskii–Moriya interaction at interfaces or in volume of non-centrosymmetric materials. Although skyrmions have been demonstrated experimentally, the general critical intrinsic relationship among fabrication, microstructures, magnetization, and the existence of skyrmions remains to be established. Here, two series of CoFeB ultrathin films with controlled atomic scale structures are employed to reveal this relationship. The amount of defects was artificially tuned by inverting the growth order, and skyrmions were shown to be preferentially formed in samples with more defects. By utilizing first-order reversal curves, the stable region and the skyrmion densities can be efficiently controlled in the return magnetization loops. These findings establish a general internal link from sample preparation to skyrmion generation and provide a general method for controlling skyrmion density. [ABSTRACT FROM AUTHOR]

A trilayer micromagnetic model based on the Landau-Lifshitz-Bloch equation of motion is utilized to study the properties of L10-FePt/TiN/L10-FePt pseudo spin valves (PSVs) in direct comparison with experiment. Theoretical studies give an insight on the crystallographic texture, magnetic properties, reversal behavior, interlayer coupling effects, and magneto-transport properties of the PSVs, in particular, with varying thickness of the top L10-FePt and TiN spacer. We show that morphological changes in the FePt layers, induced by varying the FePt layer thickness, lead to different hysteresis behaviors of the samples, caused by changes in the interlayer and intralayer exchange couplings. Such effects are important for the optimization of the PSVs due to the relationship between the magnetic properties, domain structures, and the magnetoresistance of the device. [ABSTRACT FROM AUTHOR]

The magnetic skyrmionium can be seen as a coalition of two magnetic skyrmions with opposite topological charges and has potential applications in next-generation spintronic devices. Here, we report the current-driven dynamics of a skyrmionium in a ferromagnetic nanotrack with the voltage-controlled magnetic anisotropy. The pinning and depinning of a skyrmionium controlled by the voltage gate are investigated. The current-driven skyrmionium can be used to mimic the skyrmionium diode effect in the nanotrack with a voltage gate. We have further studied the skyrmionium dynamics in the nanotrack driven by a magnetic anisotropy gradient in the absence of spin current. The performance of a single wedge-shaped voltage gate at different temperatures is studied. Our results may provide useful guidelines for the design of voltage-controlled and skyrmionium-based spintronic devices. [ABSTRACT FROM AUTHOR]

A complex transverse alternating-current (ac) susceptibility (χT) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin film recording media. The technique has been used to measure the dispersions in grain size and anisotropy field in perpendicular magnetic recording media. Applying a direct-current (dc) field perpendicular to the easy axis effectively reduces the thermal energy barrier, which leads to thermally activated switching on the time scale of the ac field applied in the easy-axis (perpendicular) direction. The dc field dependence of the resulting imaginary transverse ac susceptibility Im(χT) is sensitive to dispersions in both the grain size and the anisotropy field. The sensitivity has been used to extract the amount of both dispersions. It has been found that the extracted grain size dispersion values agree well with those obtained from plane-view transmission electron microscopy micrographs. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic damping of precessional spin dynamics in defect-controlled epitaxial grown Fe3O4(111)/Yttria-stabilized Zirconia nanoscale films by all-optical pump-probe measurements. The intrinsic damping constant of the defect-free Fe3O4 film is found to be strikingly larger than that of the as-grown Fe3O4 film with structural defects. We demonstrate that the population of the first-order perpendicular standing spin wave (PSSW) mode, which is exclusively observed in the defect-free film under sufficiently high external magnetic fields, leads to the enhancement of the magnetic damping of the uniform precession (Kittel) mode. We propose a physical picture in which the PSSW mode acts as an additional channel for the extra energy dissipation of the Kittel mode. The energy transfer from the Kittel mode to the PSSW mode increases as in-plane magnetization precession becomes more uniform, resulting in the unique intrinsic magnetic damping enhancement in the defect-free Fe3O4 film. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) constitute promising nanomedicine tools based on the possibility of obtaining different actuations (for example, heating or mechanical response) triggered by safe remote stimuli. Particularly, the possibility of performing different tasks using the same entity constitutes a main research target towards optimizing the treatment. But such a goal represents, in general, a very difficult step because the requisites for achieving efficient responses for separate actuations are often disparate – if not completely incompatible. An example of this is the response of MNPs to external AC fields, which could in principle be exploited for either magneto-mechanical actuation (MMA) at low frequencies (tens of Hz); or heat release at high frequency (0.1–1 MHz range) for magnetic fluid hyperthermia (MFH). The problem is that efficient MMA involves large torque, the required material parameters for which are detrimental to high heating, thus hindering the possibility of effective alternation between both responses. To overcome such apparent incompatibility, we propose a simple approach based on the use of anisotropic MNPs. The key idea is that the AC-frequency change must be concurrent with a field-amplitude variation able to promote – or impede – the reversal over the shape-determined anisotropy energy barrier. This way it is possible to switch the particle response between an efficient (magnetically dissipationless) rotation regime at low-f, for MMA, and a “frozen” (non-rotatable) high-energy-dissipation regime at high-f, for MFH. Furthermore, we show that such an alternation can also be achieved within the same high-f MFH regime. We use combined Brownian dynamics and micromagnetic simulations, based on real experimental samples, to show how such a field threshold can be tuned to working conditions with hexagonal-disk shape anisotropy. [ABSTRACT FROM AUTHOR]

Using the time-resolved magneto-optical Kerr effect method, helicity-dependent all-optical magnetization switching (HD-AOS) is observed in ferrimagnetic TbFeCo films. Our results reveal the individual roles of the thermal and nonthermal effects after a single circularly polarized laser pulse. The evolution of this ultrafast switching occurs over different time scales, and a defined magnetization reversal time of 460 fs is shown—the fastest ever observed. Micromagnetic simulations based on a single macro-spin model, taking into account both heating and the inverse Faraday effect, are performed which reproduce HD-AOS demonstrating a linear path for magnetization reversal. [ABSTRACT FROM AUTHOR]

Magneto-optical measurements have been applied to determine the anisotropy field of perpendicular media with a well-defined demagnetizing state. The rotation of the perpendicular magnetization component is measured as a function of the in-plane field by the Polar Kerr effect. The field range is sufficiently small to avoid domain formation and ensure coherent magnetization rotation. By fitting to a simple response function, the effective anisotropy field (H'[SUBK1] = H[SUBK1] - 4πM[SUBS]) with a well-defined 4πM[SUBS] demagnetization correction can be determined. This also enables accurate determination of the ratio of short-time coercivity H[SUB0] over anisotropy field H[SUBk], an important parameter for perpendicular recording. The H[SUB0]/H[SUBk] ratio is found to decrease with increasing intergranular coupling strength, in good agreement with our micromagnetic results. It drops from about 0.8 for weakly coupled media to 0.5 for strongly coupled media. Theoretical studies show that the effects of easy axis angular dispersion are small, about 1% error for 5° dispersion, and the rotation method measures the mean value of H[SUBk] for media with anisotropy field distribution. [ABSTRACT FROM AUTHOR]

Exchange coupling between magnetic grains is essential for maintaining the stability of stored information in magnetic recording media. Using an atomistic spin model, we have investigated the coupling between neighbouring magnetic grains where magnetic impurity atoms have migrated into the non-magnetic grain boundary. We find that when the impurity density is low, a biquadratic term in addition to the bilinear term is found to better describe the inter-granular exchange coupling. The temperature dependence of both terms is found to follow a power law behaviour with the biquadratic exchange constant decaying faster than the bilinear. For the increasing grain boundary thickness, the inter-granular exchange reduces and also decays more quickly with temperature. Further simulations of a grain at a bit boundary show an unexpected energy minimum for in-plane magnetisation. This feature is reproduced if the biquadratic exchange term is included. [ABSTRACT FROM AUTHOR]

In this paper, we study the coercivity of bit-patterned media, trapping electron-assisted magnetic recording (TEAMR), and modified TEAMR (M-TEAMR) media using a dielectric underlayer. The VAMPIRE magnetic simulator is used to model three structures of recording bits and to study the $M$ – $H$ loops using an atomistic spin model. The results show that the magnetic switching reduction in M-TEAMR and TEAMR depends on the bit size. The percentage of magnetic switching reduction in M-TEAMR is also larger than TEAMR for all bit sizes. For a bit size of $1.6 \times 1.6 \times 3.2$ nm3, the percentage of magnetic switching reduction in M-TEAMR is approximately four times higher than that in TEAMR. [ABSTRACT FROM AUTHOR]

A custom microcoil was used to generate a magnetic field pulse and a continuous wave (CW) laser was used as a heating source to study the heat-assisted effect in magnetization switching on GdFeCo thin films. Four different pulsed field strengths were chosen, and the power of the CW laser heating was varied from 0 to 180 mW. The heat-assisted enhancement was not observed when the pulsed field strength was 2400 Oe. The enhancement was visible when the pulsed field strength was reduced to 2160 Oe, and became obvious when the pulsed field strength was 1750 and 1350 Oe. These interesting results prove that CW laser heating could provide a marked improvement to the magnetization switching when the switching field is relatively small, thus making it a more applicable and economic alternative to pulsed laser heating. Simulations based on the Landau–Lifshitz–Bloch equation have also been performed and agreed well with the experimental data. The CW laser heating scheme provides a more economic and practical way to realize heat-assisted magnetization switching, which could be used for potential future heat-assisted magnetic recording technology. [ABSTRACT FROM AUTHOR]

We study spin relaxation in n-type bulk GaAs, due to the Dyakonov-Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into account electron-electron interactions within the simulations, results for the spin relaxation time-with respect to both electron density and temperature-will reach good quantitative agreement with corresponding experimental data. Our calculations contain no fitting parameters. [ABSTRACT FROM AUTHOR]

Synthetic ferrimagnets are composite magnetic structures formed from two or more anti-ferromagnetically coupled magnetic sublattices with different magnetic moments. Here, we report on atomistic spin simulations of the laser-induced magnetization dynamics on such synthetic ferrimagnets and demonstrate that the application of ultrashort laser pulses leads to sub-picosecond magnetization dynamics and all-optical switching in a similar manner as in ferrimagnetic alloys. Moreover, we present the essential material properties for successful laser-induced switching, demonstrating the feasibility of using a synthetic ferrimagnet as a high density magnetic storage element without the need of a write field. [ABSTRACT FROM AUTHOR]

A complex transverse ac susceptibility (χT) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin-film recording media. The technique has been used to measure the dispersions in grain size and the anisotropy field of perpendicular magnetic recording media. Experiments have been designed to study the key factors contributing to the anisotropy field distribution (σHk) in perpendicular media. The correlation between anisotropy dispersion, stacking faults, and recording performance have also been studied. A good correlation between stacking faults and σHK has been established. Lower stacking faults result in smaller anisotropy distribution and better media signal-to-noise ratio. The main factors controlling stacking faults are studied. Theoretical studies of the effect of interactions on the χT are also presented. [ABSTRACT FROM AUTHOR]

The validity of the application of the dissipative particle dynamics (DPD) method to ferromagnetic colloidal dispersions has been investigated by conducting DPD simulations for a two-dimensional system. First, the interaction between dissipative and magnetic particles has been idealized as some model potentials, and DPD simulations have been carried out using such model potentials for a two magnetic particle system. In these simulations, attention has been focused on the collision time for the two particles approaching each other and touching from an initially separated position, and such collision time has been evaluated for various cases of mass and diameter of dissipative particles and model parameters, which are included in defining the equation of motion of dissipative particles. Next, a multi-particle system of magnetic particles has been treated, and particle aggregates have been evaluated, together with the pair correlation function along an applied magnetic field direction. Such characteristics of aggregate structures have been compared with the results of Monte Carlo and Brownian dynamics simulations in order to clarify the validity of the application of the DPD method to particle dispersion systems. The present simulation results have clearly shown that DPD simulations with the model interaction potential presented here give rise to physically reasonable aggregate structures under circumstances of strong magnetic particle-particle interactions as well as a strong external magnetic field, since these aggregate structures are in good agreement with those of Monte Carlo and Brownian dynamics simulations. [ABSTRACT FROM AUTHOR]

Presents numerical and analytical calculations of rotational process in perpendicular recording media and examines their application to anisotropy measurement. Expression for the rotational magnetization for a noninteracting system; Role of domain formation in the rotational magnetization process; Coordinate system for the calculation.

Analyzes the design of media for ultrahigh-density perpendicular magnetic recording. Effect of intergranular exchange coupling; Role of vector fields during the write process; Challenge for media in ultrahigh-density systems.

Optical interconnect has emerged as the front-runner to replace electrical interconnect especially for off-chip communication. However, a major drawback with optical interconnects is the need for photodetectors and amplifiers at the receiver, implemented usually by direct bandgap semiconductors and analog CMOS circuits, leading to large energy consumption and slow operating time. In this letter, we propose a new optical interconnect architecture that uses a magnetic tunnel junction (MTJ) at the receiver side that is switched by femtosecond laser pulses. The state of the MTJ can be sensed using simple digital CMOS latches, resulting in significant improvement in energy consumption. Moreover, magnetization in the MTJ can be switched on the picoseconds time-scale and our design can operate at a speed of 5 Gb/s for a single link. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An atomistic model based on a classical spin Hamiltonian and a Landau–Lifshitz–Gilbert (LLG) equation was utilized to simulate and gain understanding of the magnetic, interfacial, and reversal properties of perpendicular anisotropy L10-FePt/Ag/L10-FePt pseudo spin valves, with different interfacial roughness, representing the experimentally observed behavior of the interface where the Ag spacer layer was postannealed at different temperatures. Simulation results showed that the influence of the Ag spacer on the independent switching of the FePt layers became stronger with a greater degree of interlayer mixing under higher temperature treatment. This was the result of an increased magnetic polarization of Ag with a decrease in Ag spacer thickness. Furthermore, with greater intermixing the magnetization reversal of the harder fixed FePt layer also changed from a coherent reversal process to one which took place via nucleation and propagation of reversed domains. [ABSTRACT FROM AUTHOR]

We have investigated the impact of Ag surface coating on the microstructure of CoAg core-shell nanoparticles, and the consequences for the magnetic properties. Atomic structures were simulated using a molecular dynamics approach utilizing the embedded atom method. The magnetic properties were then simulated using an atomistic approach using a classical spin Hamiltonian, taking into account the long-range nature, atomic separation and directional and phase dependence of the exchange interactions in Co. For pure cobalt nanoparticles with a diameter less than approximately 3 nm the internal crystal structure showed multiple twinned regions and the morphology of an icosahedron. The addition of a monolayer silver coating alters the internal cobalt crystal structure to a regular planar form along the cubic [111] direction with a mixture of face centred cubic (fcc) and hexagonal close packed (hcp) atomic arrangements. The local atomic environment was used to assign anisotropies to the atoms on a site by site basis. Moreover, the capping layer influences the shape of the particle and yielded a morphology similar to that of a truncated octahedron. Taking into account the effects of surface anisotropy in addition gives an overall picture of anisotropy for CoAg nanoparticles. We present the results of calculations estimating the energy barrier to magnetization reversal and the intrinsic coercivity for these particles. [ABSTRACT FROM AUTHOR]

The time variation of magnetostatic fields generated by space and time varying magnetization configurations in small perpendicular pole tips is studied. The magnetization configurations are a response to external fields driving the pole tip and soft under layer (SUL). When the system damping is sufficiently small the magnetization excitations persist for a tong time after reversal. The effects of damping parameter, position in the media, and discretization cell size on the magnitude of the time varying magnetostatic fields will be given. Decreasing the damping parameter increases the magnitude of the magnetostatic field variation. [ABSTRACT FROM AUTHOR]

For acceleration of the calculations of thermal magnetic switching, we report the use of the Voter method, recently proposed in chemical physics (also called "hyperdynamics of the infrequent events"). The method consists of modification of the magnetic potential so that the transition state remains unchanged. We have found that the method correctly describes the mean first passage time even in the ease of small damping (precessional case) and for an oblique angle between the anisotropy and the field directions Due to the costly evaluation of the Lowest energy eigenvalue, the actual acceleration depends on its fast computation. In the current implementation, it is limited to intermediate time scale and to small system size. [ABSTRACT FROM AUTHOR]

The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach. [ABSTRACT FROM AUTHOR]