We study the effect of a circular hole-shaped structural defect on the size and density of skyrmions in a perforated magnetoelectric film using the steepest descent method and Monte Carlo simulations. Achieving controllable skyrmion density opens up possibilities for the design of functional skyrmion-based devices. We show that the presence of a hole-shaped defect in the ferroelectric layer leads to a remarkable localization effect in the second (magnetic) monolayer. This effect has clear potential for practical applications as it solves the important problem of localizing skyrmions at specific predetermined positions. The defect enables stable localization of skyrmions in the magnetic layer directly beneath the hole. To verify the thermal stability of the skyrmions and the skyrmion lattice phase, we performed Monte Carlo simulations and calculated the order parameter and susceptibility. The results obtained can be useful for evaluating the “potential capabilities” of specific defect sizes and interaction parameters in magnetoelectric materials for achieving high transition temperatures in the presence of a strong in-plane Dzyaloshinskii-Moriya interaction.
The Ising machine is a promising solver for quadratic unconstrained binary optimization (QUBO) problems. Its core principle is finding the global minimum of the Ising Hamiltonian in a physical system. We propose an alternative optomechanical platform for the Ising machine solver based on a hybrid optical-electrodynamical trap that enables controllable spatial bifurcation to create artificial spin states. In this work, we present a time-multiplexing architecture to solve combinatorial optimization problems on the proposed optomechanical platform. Time division multiplexing enables scalable spin networks with Ising-type interactions across different graph topologies. We also discuss advantages and challenges of the time-multiplexing concept for a levitodynamical platform with continuous dynamics. Numerical simulations demonstrate the platform's capability to solve a 2D chessboard optimization problem, where the artificial spin network self-organizes from a disordered initial state to the global-minimum checkerboard configuration.
The coercivity for 5 mm thick magnets was enhanced by 0.85T after Tb grain boundary diffusion process (GBDP). However, the magnet slices easily stuck together due to the formation of a stalactite-like structure consisting of coarse (Nd, Tb)2Fe14B grains and (Nd, Tb)-rich phases. By pre-oxidizing the magnet surface before or after Tb coating, (Nd, Tb)-oxides formed in the outer layer during GBDP, which effectively suppressed the inter slice sticking. Excessive nonmagnetic (Nd, Tb)-oxides degrade remanence and coercivity by disrupting grain boundary continuity and hindering Tb diffusion. Pre-oxidation performed after Tb coating restricted oxygen penetration into the magnet interior during GBDP. Meanwhile, appropriate oxygen dissolution promoted the formation of a continuous Nd rich grain boundary phase, further slightly improving coercivity. Thus, pre-oxidation following Tb coating represents a promising strategy to preserve the beneficial effects of grain boundary diffusion while eliminating inter slice adhesion.
Magnetoelectric (ME) sensors are traditionally characterized under spatially uniform magnetic fields, where their performance is summarized by the ME coupling coefficient. This approach implicitly treats the sensor as a lumped element and neglects its spatial extent. In practical applications, sensing scenarios involve localized or gradient dominated magnetic fields, where the spatial distribution of excitation directly influences the generated strain and output voltage in the ME sensor. In this work, the response of the strain-mediated ME laminate is systematically investigated under both uniform magnetic excitation and dipole non-uniform spatially varying magnetic fields. A spatial sensitivity mapping framework is introduced to quantify ME sensor behavior under non-uniform excitation. Experimental measurements of dipole-induced scaling and lateral response show good agreement with numerical predictions, validating the proposed approach. The results reveal the localized strain concentration, strong distance dependent decay, and directional sensitivity that cannot be inferred from uniform field characterization alone. These findings demonstrate that uniform-field metrics are insufficient for predicting real-world sensor performance and establish spatial characterization as a necessary complement for practical ME sensing applications such as magnetic particle mapping, and health monitoring in mechanical systems.
Scalable integration of multiferroics and robust magnetic control without external magnetic fields are key requirements for voltage-driven spintronic devices. Here, we demonstrate an industry-compatible approach based on radio frequency magnetron sputtering to grow single-crystalline epitaxial BiFeO3 (BFO), 10% Co B-site-doped BiFeO3 (BFCO), and 10% La A-site-doped BiFeO3 (LBFO) thin films on SrTiO3(001) and integrate them with CoFeB to form Ta/CoFeB/(BFO, BFCO, and LBFO)/STO heterostructures. Powder X-ray diffraction (XRD) confirms rhombohedral BFO-based targets, while high-resolution XRD establishes phase-pure (00 & ell;)-oriented epitaxy; omega-rocking curves show full width at half maxima < 0.5 degrees and reciprocal space mapping verifies coherent in-plane strain. Piezoresponse force microscopy confirms robust local ferroelectric switching in all films. Among the compositions, BFCO exhibits the strongest magnetic response (M-s approximate to 77 emu & centerdot;cm(-3) and H-c approximate to 348 Oe) and produces the largest interfacial exchange-coupling signature when coupled to CoFeB: the CoFeB coercivity increases to similar to 843 Oe in Ta/CoFeB/BFCO/STO compared with similar to 30 Oe for Ta/CoFeB/Si. These results establish sputtered epitaxial BFCO as a scalable platform for engineering strong interfacial pinning in multiferroic/ferromagnet stacks, enabling low-power, high-density voltage-controlled spintronic memories beyond conventional spin-transfer torque magnetoresistive random-access memory.
We present analytical expressions for calculating the dynamic susceptibility of nanostructured magnetic systems and apply them to micromagnetic simulations of vortex dynamics in rectangular Fe and Permalloy (Ni80Fe20, Py) nanoelements. After magnetic saturation and relaxation to remanence, stable vortex states are obtained, and their excitations are identified through the chi(xx) component of the susceptibility tensor under a weak transverse oscillating field. For 60 nm & times; 80 nm & times; 30 nm nanoelements, Fe exhibits excitations at 0.65, 1.55, and 2.56 GHz, while Py shows excitations at 0.29, 0.75, and 0.97 GHz. The lowest-frequency mode is localized in the vortex core, whereas the higher frequency modes correspond to edge excitations and excitations localized at internal regions of the nanoelement. The reduced frequencies of Py excitations are attributed to its lower saturation magnetization and exchange stiffness
Magnetic tunnel junctions with voltage-controllable telegraphing between the parallel and antiparallel states were combined with hybrid circuits to create probabilistic bit modules. The time-dependent behavior was measured both when these devices were free running and when they were coupled together to form stochastic logic gates. Two modules were used to create a nearly deterministic NOT gate. A stochastic AND gate was demonstrated using a combination of three modules, and a statistical preference for microstates consistent with the AND gate truth table was observed. A metric is developed for quantifying the performance through pairwise comparison of microstate probabilities.
In this study, a modeling and benchmarking framework is presented to assess compact two-terminal (2T) in-plane magnetic anisotropy spin-orbit torque magnetic random-access memory (IMA SOT-MRAM) cells. Although a previously proposed one-transistor one-magnetic tunnel junction configuration, with its 2T configuration, offers a more compact cell design that improves the cell density compared to a three-terminal (3T) design, it suffers from significant current crowding at the edge of the device and does not provide any notable advantage in terms of write time or energy. Here, we analyze a 2T variant incorporating a fixed layer with a length half of the free layer; this increases the effective path electrons pass through the SOT layer and provides a measurable benefit in terms of write energy and conduction current density. Two materials for the SOT channel-AuPt and beta-W-are investigated. With the beta-W SOT channel, the IMA 2T SOT-MRAM cell featuring a half-fixed layer achieves a 25% decrease in maximum conduction current density and a 16% decrease in write energy compared to the conventional 3T IMA SOT-MRAM. Also, the maximum conduction current densities for the IMA cases are significantly lower compared to those of the field-assisted perpendicular magnetic anisotropy case. These results indicate that the half-fixed 2T architecture-when paired with CMOS-compatible beta-W -offers a practical path to denser, lower energy in-plane SOT-MRAMs.
Combining spin-orbit (SOT) and spin-transfer torques (STT) provides a practical approach for field-free switching in spin-orbit torque magnetic random-access memory (SOT-MRAM), a prerequisite for industrial deployment, but can compromise reliability through phenomena such as backhopping, especially in top-pinned stacks commonly used for SOT-MRAM. We investigate the write error rate (WER) of combined SOT + STT switching in top-pinned devices that are not optimized for STT switching. Experiments reveal clear indications of STT-induced backhopping and a pronounced field-free SOT switching asymmetry between AP-to-P and P-to-AP transitions. Our macrospin model, using two coupled Landau Lifshitz Gilbert equations for the free and the reference layers, qualitatively reproduces this asymmetry and reveals an intermediate loss-of-determinism regime in addition to the well-known backhopping region. Based on these simulations, we propose mitigation strategies and experimentally demonstrate that STT pulse shaping reduces WER and improves switching robustness in the presence of device imperfections.
Biological neurons exhibit diverse spiking behaviors, such as fast, phasic, and bursting modes, which are essential for efficient neural communication. However, most spintronic neuromorphic systems remain limited to simplified leaky-integrate-and-fire (LIF) models due to the difficulty of realizing complex neuronal dynamics in hardware. In this work, we develop a reconfigurable spiking neuron based on the intrinsic dynamics of antiferromagnetic (AFM) skyrmions driven by an anisotropy gradient in structured nanotracks. By engineering an anisotropy gradient along a trapezoidal nanotrack, the device achieves multimodal LIF functionality without external current injection or additional hardware overhead. The nanotrack geometry naturally enables leaky integration, while controlled anisotropy modulation allows dynamic reconfiguration between fast, phasic, and bursting spiking modes. An artificial neural network constructed from these AFM skyrmions as neurons demonstrates improved Iris flower classification performance compared to conventional LIF-based models, highlighting their potential as an energy-efficient and bio-plausible neuromorphic computing platform.
Increasing switching frequency reduces magnetic volume, but conventional ferrites, used from tens to hundreds of kilohertz, cannot sustain the temperature and frequency ranges demanded by current and emerging wide bandgap and ultrawide bandgap devices. This work presents a novel magnetic material architecture combining nanocrystalline magnetic material and multiferroic layers for megahertz power conversion. The high saturation flux density of nanocrystalline alloys supports miniaturization but is traditionally constrained by excessive losses above 10 kHz. A revolutionary multiferroic material with solid-state cooling via caloric materials is defined that will enable the next generation of magnetic devices for wide-bandgap-integrated designs. This letter highlights the fundamental physics behind this capability alongside early development of a finite element analysis for the multiferroic-based magnetic device using ANSYS, showing that the core achieves more uniform thermal distribution and reduces peak temperature by 9 C-degrees compared to conventional ferrites.
A time-varying magnetic field induces electric currents in a conductive object, which in turn induces a force-torque wrench on the object that is not due to ferromagnetism. Prior work empirically modeled the wrench induced in a solid sphere by a rotating magnetic dipole (RMD) field, and then used this model to perform contactless manipulation using multiple RMD field sources, motivated by application in on-orbit satellite servicing and space-debris capture. In this letter, we measure the induced wrench on a conductive, nonferromagnetic cube-which, unlike on a sphere, is not invariant to orientation-in six canonical configurations, and we compare it to that of a sphere with identical volume. Results show that such a spherical model provides a reasonable orientation-invariant approximation of a cube. Further, the induced wrench can be bounded by considering the induced wrenches on spheres with +/- 15% volume.
We present a micromagnetic study of remanent magnetic states in square Fe and permalloy nanorings, emphasizing the roles of field history and geometric confinement. Remanent configurations are obtained by saturating the rings under different field orientations and reducing the field to zero. The results reveal strong path dependence: diagonal and perpendicular saturation stabilize onion-like and vortex states, respectively, whereas edge-field saturation induces transitions among buckle-like, in-plane vortex, and fully three-dimensional vortex states. Phase diagrams show that these transitions are governed primarily by magnetostatic interactions, with stronger effects in Fe due to its higher saturation magnetization. These findings provide a strategy for deterministic remanent-state selection in square nanorings, relevant to multi-state magnetic and spintronic applications.
This letter presents an eccentric inverted-cone three-dimensional transcranial magnetic stimulation (TMS) coil to address the poor focusing ability and small effective stimulation depth in commercial TMS coils. The performance of the coil is compared with that of several commercial and theoretical coils via finite element modeling. Spherical head model simulations reveal that the coil outperforms existing coils in terms of focusing ability and effective stimulation depth. Furthermore, employing a dual-coil combination effectively enhances the maximum induced electric field strength and increases the focusing ability and effective stimulation depth of the signal.
In this letter, we demonstrate for the first time the preparation of bulk L1(0)-FeNi embedded in an fcc FeNi by alloying Fe and Ni during casting with 5%-10% indium metal and annealing at 350 degrees C for a week. From X-ray diffraction, magnetization, and M & ouml;ssbauer data, we have strong indications that the L1(0)-FeNi phase is formed and coexists with the cubic A1-FeNi at a ratio of 30/70 for the sample with 5% In and 20/80% for the sample with 10% In, as derived from X-ray diffraction. This finding is supported by the M & ouml;ssbauer data, where the ratio of L1(0)-FeNi to A1-FeNi is 48/52 and 24/76, respectively. The morphology of the alloys is sponge-like and very brittle, and the final In stoichiometry is much less than the nominal one.
Untethered magnetic devices (UMDs) hold significant clinical potential for removing blood clots. However, in the complex intravascular environment, their locomotion may be disturbed. Such disturbances can lead to variations in the magnetic gradient force exerted on the UMD, increasing the risk of vascular damage. Therefore, evaluating the magnetic gradient force acting on the UMD under worst-case conditions is essential for risk mitigation. In this letter, we a novel method to estimate the upper and lower bounds of the worst-case magnetic gradient force acting on the UMD, with actuation provided by two synchronized rotating magnetic dipoles. To assess the robustness of the algorithm, we conducted a Monte Carlo simulation in which the dipole directions of the two synchronized rotating magnetic dipoles and the dipole direction of the UMD were randomly varied 1 000 000 times in the three-dimensional space to simulate all possible scenarios that may be encountered by the UMD in intravascular environments. The simulation results indicate that the worst-case magnetic gradient force remains below the upper bound predicted by the algorithm, thereby validating its effectiveness.
Increasing switching frequency reduces magnetic volume, but conventional ferrites, used from tens to hundreds of kilohertz, cannot sustain the temperature and frequency ranges demanded by current and emerging wide bandgap and ultra-wide bandgap devices. This work proposes a novel magnetic material architecture combining nanocrystalline magnetic material and multiferroic layers for MHz power conversion. The high saturation flux density of nanocrystalline alloys supports miniaturization but is traditionally constrained by excessive losses above 10 kHz. A revolutionary multiferroic material with solid-state cooling via caloric materials is defined that will enable the next generation of magnetic devices for WBG-integrated designs. This letter highlights the fundamental physics behind this capability alongside early development of a finite element analysis for the multiferroic-based magnetic device using ANSYS, showing that the proposed core achieves more uniform thermal distribution and reduces peak temperature by 9 $^{\circ }$C compared to conventional ferrites.
Single-dot Nd-Fe-B micromagnets were fabricated using the pulsed laser deposition-laser-induced forward transfer (PLD-LIFT) technique, and their magnetic properties were systematically examined. Hysteresis measurements with a vibrating sample magneto meter revealed that the coercivity (H-c) was nearly independent of laser power, whereas an increased defocus rate (DF rate) enhanced H-c up to 340 kA/m. Scanning electron microscopy and cross-sectional scanning transmission electron microscopy analyses revealed that each dot comprises grains ranging from submicrometer to micrometer scale. Within these grains, an Nd2Fe14B core is encapsulated by an Fe-rich matrix containing dispersed Nd oxides. The thickness of this Fe-rich outer shell modifies the exchange pathway at the Nd2Fe14B/Fe interface, giving rise to the characteristic two-step demagnetization. Guided by these observations, a simplified Nd2Fe14B/alpha-Fe core-shell model was developed and evaluated through micromagnetic simulations, which successfully reproduced the stepwise reversal and clarified DF's role in suppressing soft-phase connectivity and improving loop squareness. Collectively, these findings identify DF rate as the dominant processing parameter and provide practical guidelines for tailoring PLD-LIFT Nd-Fe-B micromagnets toward microelectromechanical systems applications.
Self-demagnetizing fields in uniformly magnetized flat magnets limit the surface magnetic flux density and output power of magnetic microelectromechanical systems (MEMSs). In laser-assisted heating magnetization (LAHM), the laser locally reduces the coercivity, and a uniform reverse magnetic field subsequently reverses the magnetization. LAHM was developed to produce fine multipole patterns and address these performance limitations. This study extends LAHM by superimposing a distributed external magnetic field tailored to the target pattern. The field is generated by a prepatterned multipole master NdFeB magnet (B-r = 1.30 T and H-cj = 2388 kA/m) placed on a uniform reverse-field source, which strengthens the local magnetizing field in the target areas and attenuates it elsewhere. Experiments employing 0.3 mm thick NdFeB samples demonstrate that distributed-field LAHM increases the magnetization ratio by 10.8% and the peak-to-peak surface magnetic flux density by 54.2 mT compared with conventional uniform-field LAHM. These results indicate a potential route to higher performance multipole magnets for MEMS applications.
