Magnetization Reversal Research Articles

Magnetic field direction dependent magnetization reversal in synthetic antiferromagnets based on first-order reversal curve analysis

Magnetic field direction dependent magnetization reversal in synthetic antiferromagnets based on first-order reversal curve analysis

Optically Readable Multilevel Magnetic Memory States in Perpendicularly Exchange-Biased Ferromagnetic Multilayers.

The construction of multilevel magnetic states using materials with perpendicular magnetic anisotropy (PMA) offers a novel approach to enhancing the storage density and read/write efficiency of nonvolatile magnetic memory devices. In this study, optically readable multilevel magnetic domain states are achieved by inducing asymmetric interlayer interactions and decoupling the magnetic reversal behavior of individual ferromagnetic (FM) layers in exchange-biased FM multilayers with PMA. Hepta-level magnetic domain states are formed in [Co/Pt]n FM multilayers grown on an antiferromagnetic Fe2O3 layer within a relatively low magnetic field range of ∼±400Oe. Raising and lowering operations between states are demonstrated to be achievable, enabling the writing of new information without the need for initialization in multilevel magnetic memory applications. This design concept, leveraging multilevel magnetic domain states and facilitating noncontact optical reading of stored information, demonstrates the potential to enhance the storage density of nonvolatile magnetic memory devices as it eliminates the need for electrical circuits typically required in other resistive memory technologies.

Demagnetization Process of Nd‐Fe‐B Sintered and Ferrite Magnets

The magnetization reversal mechanism for Nd‐Fe‐B sintered and ferrite magnets was investigated using magnetic measurements and soft X‐ray magnetic circular dichroism microscopy. In magnetization reversal, discrete reversals of crystal grains occurred first in the demagnetized field region, which was lower than the coercivity. In the next step, clusters of reversed grains were formed by reversals in crystal grains around the discrete reversed grains. For highly aligned magnets, the cluster sizes at the coercivity increased with decreasing temperature, and also varied with composition. The alignment and angular dependences of the coercivity varied with cluster size, which depended on the number of discrete magnetization reversal grains that occurred in the demagnetizing field that was lower than the coercivity. Hence, if the number of discrete reversal grains was large, the cluster size was small; conversely, if the number of discrete reversal grains was small, the cluster size was significant. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Subduction‐Related Volcanic Activity as a Proxy for Global Subduction Flux Over the Past Billion Years, and Its Correlation With Geomagnetic Superchrons

AbstractWe investigate the frequency of subduction‐related volcanic events over the past billion years. Our analysis reveals distinct peaks and troughs interpreted as significant fluctuations in global subduction flux. This approach has the advantage of being independent of paleogeographic reconstructions. However, it does not provide information on the spatial distribution of thermal heterogeneities at the core‐mantle boundary. This likely explains why the long‐term evolution of global subduction flux does not correlate in any simple way with the frequency of geomagnetic polarity reversals throughout the Phanerozoic. As an additional parameter, we suggest focusing on how variations in the Earth's inertia, due to changing subduction configurations over time, influence the thermal conditions at the core‐mantle boundary and, consequently, the magnetic reversal frequency.

Magnetization reversal of a ferromagnetic Pt/Co/Pt film by helicity dependent absorption of visible to near-infrared laser pulses

Magnetization reversal of a ferromagnetic Pt/Co/Pt film by helicity dependent absorption of visible to near-infrared laser pulses

Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque

We investigate the magnetization reversal of a perpendicularly magnetized nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOTs). Our numerically simulated findings demonstrate that both the field-like (FL) and damping-like (DL) components of SOT in CCP can be efficiently utilized to induce ultrafast magnetization reversal without any symmetry-breaking means. For a wide frequency range of the CCP, the minimal current density is significantly smaller compared to the current density of conventional SOT-reversal. This ultrafast reversal is achieved due to the CCP triggering enhanced energy absorption (emission) of the magnetization from (to) the FL- and DL-components of SOT before (after) crossing over the energy barrier. We also verify the robustness of the CCP-driven magnetization reversal at room temperature. Moreover, this strategy is applicable also to induce field-free ultrafast and efficient switching of perpendicular synthetic antiferromagnetic and ferrimagnetic (SFi) nanodevices. The minimal current density of deterministic switching of the SFi system decreases significantly with the reduction of one layer's magnetization, mainly because the SOT amplitude is inversely proportional to the saturation magnetization. Therefore, this study enriches the basic understanding of field-free SOT-reversal and provides a way to realize ultrafast SOT-MRAM devices with various free layer designs.

Impacts of β-diketonate terminal ligands on slow magnetic relaxation and luminescence thermometry in dinuclear DyIII single-molecule magnets.

Lanthanide-based Single-Molecule Magnets (SMMs) with optical and magnetic properties provide a means to understand intrinsic energy levels of 4f ions and their influence on optical and magnetic behaviour. Fundamental understanding of their luminescent and slow relaxation of the magnetization behaviour is critical for targeting and designing SMMs with multiple functionalities. Herein, we seek to investigate the role of DyIII coordination environment and fine electronic structure on the slow magnetic relaxation and luminescence thermometry. Our findings are illustrated through two distinct DyIII complexes, [Dy2(bpm)(hexd)6] (1) and [Dy2(bpm)(hpd)6] (2), (bpm = 2,20-bipyrimidine, hexd = 2,4-hexanedione, hpd = 3,5-heptanedione), by comparing their features with a family of DyIII dinuclear species bridged by bpm. These findings highlight that the hexd- and hpd- ligands exhibit a similar effective barrier to the reversal of magnetization (280-290 K). The values are among the highest for dinuclear DyIII complexes bridged by bpm, due to the low distortion of the DyIII coordination polyhedra and the long Dy-N equatorial bonds. Furthermore, the luminescence performance is affected by the triplet state energy of the terminal ligand, influencing ligand-to-DyIII energy transfer. The hpd- ligand's higher T1 state energy leads to poor ligand-to-DyIII energy transfer, limiting the use of 2 for luminescence thermometry. Conversely, this issue is absent in 1, which offers a relative thermal sensitivity of 0.1 to 0.7% K-1 (10 to 60 K) with a temperature uncertainty below 1 K. These findings contribute to our understanding of lanthanide-based SMMs and facilitate the design of multifunctional materials with tailored magnetic and luminescent properties for molecular electronics and beyond.

Design of spike-timing-dependent plasticity synapses based on CoPt-SOT device and its application in all-spin spiking neural network

Spintronic could be used to simulate synapses or neurons due to its multistate storage characteristics. In this work, a reliable design of all-spin spiking neural networks (SNN) based on spin–orbit torque (SOT) devices has been proposed in A1 CoPt single layer. The CoPt-SOT devices exhibited field-free SOT switching, and the magnetization reversal mechanism was inferred to be a combination of domain nucleation and domain-wall propagation as observed through magneto-optical Kerr microscopy images. Moreover, the current-induced SOT switching process of the device exhibited stable multistate magnetic switching behavior, which can be controlled by varying the amplitude and pulse width of the current pulse. Meanwhile, the spike-timing-dependent plasticity (STDP) curve was inverted when the SOT switching polarity was reversed by different magnetic fields, and the change in anomalous Hall resistances (ΔRH) in the STDP curve was linearly related to the SOT switching ratio. In addition, at the zero magnetic field, we constructed an all-spin SNN using STDP synapses and leaky integrate-and-fire neurons of CoPt-SOT devices. The handwritten digits recognition rate of this all-spin SNN network was 89.9%. These results substantiate that the CoPt single layer represents a promising hardware solution for high-performance neuromorphic computing, with applicability in the domain of SNN.

Study of Magnetization Reversal Processes of Cobalt Nanowires Using NMR and Radiofrequency Resonance Magnetometry Methods

Study of Magnetization Reversal Processes of Cobalt Nanowires Using NMR and Radiofrequency Resonance Magnetometry Methods

Programmable Magnetic Hysteresis in Orthogonally-Twisted 2D CrSBr Magnets via Stacking Engineering.

Twisting 2D van der Waals magnets allows the formation and control of different spin-textures, as skyrmions or magnetic domains. Beyond the rotation angle, different spin reversal processes can be engineered by increasing the number of magnetic layers forming the twisted van der Waals heterostructure. Here, pristine monolayers and bilayers of the A-type antiferromagnet CrSBr are considered as building blocks. By rotating 90 degrees these units, symmetric (monolayer/monolayer and bilayer/bilayer) and asymmetric (monolayer/bilayer) heterostructures are fabricated. The magneto-transport properties reveal the appearance of magnetic hysteresis, which is highly dependent upon the magnitude and direction of the applied magnetic field and is determined not only by the twist-angle but also by the number of layers forming the stack. This high tunability allows switching between volatile and non-volatile magnetic memory at zero-field and controlling the appearance of abrupt magnetic reversal processes at either negative or positive field values on demand. The phenomenology is rationalized based on the different spin-switching processes occurring in the layers, as supported by micromagnetic simulations. The results highlight the combination between twist-angle and number of layers as key elements for engineering spin-switching reversals in twisted magnets, of interest toward the miniaturization of spintronic devices and realizing novel spin textures.

Polyoxometalates as advanced-performance anions for ∼D5h Dy(III) single-ion magnets.

We enhance single-ion magnet (SIM) magnetisation reversal barriers by engineering the second coordination sphere, substituting conventional small monoanions with a bulky polyoxometalate (POM) trianion. Importantly, our approach serves as a model for creating new high-performance multifunctional hybrid materials.

A fluorobenzene-bound dysprosium half-sandwich dication single-molecule magnet.

Dysprosium single-molecule magnets (SMMs) with two mutually trans-anionic ligands have shown large crystal field (CF) splitting, giving record effective energy barriers to magnetic reversal (U eff) and hysteresis temperatures (T H). However, these complexes tend to be bent, imposing a transverse field that reduces the purity of the m J projections of the CF states and promotes magnetic relaxation. A complex with only one charge-dense anionic ligand could have more pure CF states, and thus high U eff and T H. Here we report an SMM with this topology, a half-sandwich Dy(iii) complex [Dy(Cp*)(FPh)6][{Al[OC(CF3)3]3}2(μ-F)]2 (1-Dy; Cp* = C5Me5), and its Y(iii) analogue 1-Y; 1-Dy exhibits U eff = 545(30) cm-1 and T H = 14 K at sweep rates of 22 Oe s-1. The Cp* ligand imposes a strong axial CF, which is assisted by one axial fluorobenzene; the five equatorially-bound neutral fluorobenzenes present only weak transverse interactions to give a pseudo-pentagonal bipyramidal geometry. The salt metathesis reaction of 1-Y with KCp''' (Cp''' = {C5H2(SiMe3)3-1,2,4}) gave the sandwich complex [Y(Cp''')(Cp*)(FPh)2][{Al[OC(CF3)3]3}2(μ-F)] (4-Y), showing that the fluorobenzenes of 1-Y are easily displaced. We envisage that these methodologies could be adapted in future to prepare high-performance axial Dy SMMs with ligands that are more sterically demanding than Cp*.

Study of the magnetoelastic phase transition in near equiatomic FeRh alloys through T-FORC analysis and neutron diffraction

Fe100-xRhx alloys with x ∼ 50 undergo a first-order magnetoelastic phase transition close to room temperature from the low-temperature antiferromagnetic (AFM) to the high-temperature ferromagnetic (FM) state. For Fe50Rh50, the AFM-FM-AFM transitions may occur involving various coexistent mechanisms. Although the Fe49Rh51 composition closely resembles the equiatomic counterpart, its first-order phase transition exhibits notable disparities, whose underlying process remains unexplained. We combined neutron thermo-diffraction and magnetization measurements to study the phase transformation in the two alloys. The Kolmogorov-Johnson-Mehl-Avrami (KJMA) model and temperature first-order reversal curve (T-FORC) analysis are applied to explore this matter. The techniques were applied to both alloys, Fe50Rh50 and Fe49Rh51, to use the former as reference to emphasize the distinct characteristics of the latter. The study highlights the defect-based growth hindering in Fe50Rh50 and the almost complete absence of it in Fe49Rh51, accompanied by a significant effect of the FM phase magnetostatic field. This work presents a new way to obtain detailed information from the T-FORCs by analyzing their T-derivative curves. This method indicates that the superposition of applied and magnetostatic fields causes the notable differences observed in alloys with such close atomic composition. It reveals and explains peculiar features of the Fe49Rh51 temperature-driven transition, such as the anomalous cross-over of the first-order reversal magnetization curves at low temperatures, that could pave the way to a deeper understanding of the mechanisms driving the magnetostructural phase transition in these alloys.

Effects of grain boundary phases on recoil loops by in situ observation of magnetization behavior in nanocrystalline PrNd–Fe–B magnets

The grain boundary phase (GBP) has a significant influence on the magnetization behavior in nanocrystalline PrNd–Fe–B magnets. The current study demonstrates that reversible/irreversible magnetization behavior and the phenomenon of open recoil loops are related to both the nature of GBPs and the magnetization state by in situ observation. The optimization of GBPs nature (increase the volume fraction and improve the composition of GBPs) leads to the suppression of reversible magnetization behavior and the phenomenon of open recoil loops at low fields. Since the asymmetric magnetic domain structure appears only at low cycle fields, the openness phenomenon originates from the weak pinning grain boundaries (GBs). In addition, optimization of the GBPs also enhances pinning strength and uniformity, which contributes to the domain walls being pinned in the GBs at higher external fields. At this moment, the domain wall is dominated by irreversible magnetization behavior, and the openness phenomenon disappears. This proves that the coercivity mechanism is transformed from inhomogeneously weak pinning to homogeneously strong pinning with the optimization of GBPs. Consequently, the coercivity and squareness factor are significantly enhanced. This study sheds light on the understanding of the effects of GBP's nature on recoil loops and coercivity mechanism, and it also provides significant guidance for the development of advanced permanent magnets.

Epitaxial growth of CoFe/Ge stacked structures on a perpendicularly magnetized MnGa alloy

Abstract For high density and low-power-consumption MRAM applications, the combination of a low resistive tunnel barrier and perpendicular magnetized magnetic layers is required. Here, we experimentally explore the growth of an all-epitaxial spin-valve structure with a perpendicularly magnetized MnGa alloy and semiconductor Ge. Using magnetron sputtering, solid phase epitaxy (SPE), and molecular beam epitaxy (MBE) methods, we stack the MnGa, Ge, and ferromagnetic CoFe layers, respectively. Although an unintentional Mn-based oxide layer is formed between MnGa and Ge, the Ge thin layer is able to be epitaxially grown even on the MnGa alloy. From the magnetometry, we find that the top CoFe and the bottom MnGa layers are magnetically decoupled and spin-valve like magnetization reversals are seen. This study enables us to fabricate a CoFe/Ge stacked structure on MnGa.

Magnetization reversal of perpendicular magnetic anisotropy multilayers on polymeric substrates for flexible spintronics applications

Earlier demonstrations of spintronic functionality on flexible substrates have highlighted the potential for spintronics in flexible electronics applications. However, for device applications, the relationship between global magnetization reversal, as measured by hysteresis, and the local reversal processes of nucleation and growth of magnetic domains need to be understood for magnetic systems on flexible substrates. This study compares the local magnetization reversal behavior of perpendicularly magnetized Pt/CoFeB/Pt and Pt/Co/Pt on rigid and flexible polymeric substrates using magneto-optical Kerr effect magnetometry and microscopy. It is shown that while the magnetic hysteresis is comparable, the local details of the nucleation and field driven reversal are quite different and are attributed to the greater variability of the surface structures of the polymeric substrates, which has implications for consistency in device performance.

Stein’s Method and a Cubic Mean-Field Model

In this paper, we study a mean-field spin model with three- and two-body interactions. In a recent paper (Ann Henri Poincaré, 2024) by Contucci, Mingione and Osabutey, the equilibrium measure for large volumes was shown to have three pure states, two with opposite magnetization and an unpolarized one with zero magnetization, merging at the critical point. The authors proved a central limit theorem for the suitably rescaled magnetization. The aim of our paper is presenting a prove of a central limit theorem for the rescaled magnetization applying the exchangeable pair approach due to Stein. Moreover we prove (non-uniform) Berry–Esseen bounds, a concentration inequality, Cramér-type moderate deviations and a moderate deviations principle for the suitably rescaled magnetization. Interestingly we analyze Berry–Esseen bounds in case the model-parameters (Kn,Jn) converge to the critical point (0, 1) on lines with different slopes and with a certain speed, and obtain new limiting distributions and thresholds for the speed of convergence.

Two dimensional MoF3 and Janus Mo2F3X3(X = Cl, Br, I): intrinsic ferromagnetic semiconductor, large perpendicular magnetic anisotropy, and hole-induced room-temperature ferromagnetism

Abstract Two-dimensional (2D) ferromagnetic (FM) semiconductors with high Curie temperature (T c ) and large perpendicular magnetic anisotropy (PMA) are promising for developing next-generation magnetic storage devices. In this work, we investigated the structural, electronic, and magnetic properties of MoF3 and Janus Mo2F3 X 3 (X = Cl, Br, I) monolayers by first-principles methods. These materials are 2D FM semiconductors with large PMA and half-semiconducting character as both VBM and CBM belonging to the spin-up channel. Biaxial strain can modulate band gap, reverse easy magnetization axis, and induce magnetic phase transitions in MoF3 monolayer and its Janus structures. Compared to MoF3 monolayers, Janus Mo2F3 X 3 monolayers can preserve the structural ability and the FM ground state over a wider range of strain. The magnetic anisotropy energies (MAEs) of these 2D materials can be enhanced to greater than 1 meV/Mo by tensile strains. Intrinsic T c of MoF3 monolayer and its Janus structures are less than 110 K and are insensitive to strain. However, hole doping with a feasible concentration can achieve a room-temperature half-metallicity in these 2D materials. The required hole concentration is lower in Janus Mo2F3 X 3 monolayers than MoF3 monolayer. Our results indicate that MoF3 and Janus Mo2F3 X 3 (X = Cl, Br, I) monolayers are promising candidates for 2D spintronic applications and will stimulate experimental and theoretical broad studies.

Influence of physical and material parameters on switching current density in perpendicular STT-MTJ: a micromagnetic study

Abstract Switching in magnetic tunnel junctions (MTJs) is considered to be coherent according to the macrospin model but above a critical characteristic length (R c ) this process becomes incoherent. As a result, switching becomes a complex process and affects the switching current density (J c ). We designed a spin transfer torque (STT) based single barrier perpendicular MTJ (SMTJ) and observed the influence of the junction size and exchange stiffness constant (Aex) on the switching process through micromagnetic simulations performed on Object Oriented Micromagnetic Framework (OOMMF). It was found that coherent switching occurred only for junction diameter ≤20nm and showed dependence on Aex as well. The influence of damping constant and anisotropy on J c is studied and the mechanism of magnetic reversal through domain formation is revisited in this work. Furthermore, Double barrier MTJ (DBMTJ) stack was designed, which showed increased STT efficiency in switching time with a requirement of J c lower by 42.86% compared to SMTJ.

Exploring Magnetic Disorder in Inverted Core-Shell Nanoparticles: The Role of Surface Anisotropy and Core/Shell Coupling.

In this work, we have studied the effect of internal coupling in magnetic nanoparticles with inverted core-shell structure (antiferromagnet-ferrimagnet) and also magnetic surface anisotropy, performing Monte Carlo simulations based on a micromagnetic model applied in the limit of lattice size equal to the crystalline unit cell. In the treatment, different internal regions of the particle were labeled in order to analyze the magnetic order and the degree of coupling between them. The results obtained are in agreement with experimental observations in CoO/CoFe2O4 and ZnO/CoFe2O systems, which we have taken as reference. It is observed that the surface anisotropy decreases the coercive field and the blocking temperature of the system. However, the core/shell coupling improves these properties and magnetically hardens the system. Our study shows that a significant magnetic stress is generated in the system, leading to magnetic disorder in the spins of the particle interface. On the other hand, in cases of high surface anisotropy, within a range of interfacial exchange values, a clear magnetic disorder is observed in the shell, which leads to anomalous behavior because the magnetization reversal process is no longer coherent.&#xD.