Identifying nonlinear interactions among magnons is crucial for advancing the field of magnonics and developing next-generation spintronic devices. In this work, we report the experimental observation of nonlinear magnon mode hopping and hysteretic behavior in a synthetic antiferromagnet (SAF). Under strong radio-frequency excitation, the magnon system exhibits abrupt transitions between acoustic and optic modes, accompanied by GHz-scale frequency jumps-orders of magnitude larger than previously reported in magnon-based hybrid systems. We further show that this mode hopping is hysteretic, reflecting multistable nonlinear dynamics, and support these findings through theory and micromagnetic simulations. These results establish a new regime of nonlinear magnon dynamics, going beyond previously reported strong-coupling effects, and highlight the potential of SAFs as platforms for magnon-based frequency converters and switches for information processing.

Physical reservoir computing (RC) utilizing spin dynamics in serial magnetic bits has been demonstrated based on a micromagnetic simulator. An 8-layered cylindrical magnetic wire stores 3 rewritable bits as up/down magnetization directions and the spin dynamics in the top layer is detected as a time-series response signal to a time-series pulse currents. The dynamical properties were found to change with the bit pattern. Using time-domain signals from all the 8 bit patterns, RC was performed to achieve high computational capacities in two benchmark tasks. With exploration of the number of bit patterns, a scalable guideline for performance enhancement was found.

We investigated the dependence of anisotropic magnetoresistance (AMR) on the layer thickness and Co composition of Co-rich/Pt-rich CoPt alloy multilayer nanowires fabricated by dual-bath electrodeposition using nanoporous templates. Single-nanowire current-perpendicular-to-plane (CPP) electrical transport measurements revealed that reducing the individual layer thickness to a few nanometers significantly enhanced the AMR ratio, yielding a value that was 2.7 times higher than that of single-layer CoPt alloy nanowires. This enhancement might be attributed to increased interfacial spin-dependent scattering in the multilayer structure under CPP transport. In addition, the Co composition of the Co-rich layers had little effect on the AMR ratio in the high-field saturation region. In contrast, clear differences in AMR behavior were observed at low magnetic fields, indicating that the Co composition influenced the magnetization rotation process rather than the intrinsic anisotropic resistance. These findings elucidated the mechanisms underlying AMR enhancement in multilayer nanowires and provided insight into interface-dominated spin-dependent transport for the development of high-density magnetic sensors and magnetic memory devices.

The exploitation of crystal-lattice symmetries to engineer angular momentum transfer between structured light and magnons marks a novel frontier for optomagnonic research. In Brillouin light scattering, when focused light propagates parallel to an external magnetic field and interacts with ferromagnetic uniform magnons, only optical-vortex scattering is expected to be permitted. Due to the combined effects of magneto-optical coupling and optical spin-orbit interaction, the transfer of magnon spin angular momentum to photon orbital angular momentum allows for this distinctive scattering phenomenon. Here, we experimentally demonstrate that, for a specific ferromagnetic crystal orientation, Gaussian-beam scattering coexists with the optical-vortex scattering, contrary to conventional expectations based on angular momentum conservation between magnons and photons. We show that the crystal lattice, via the rotational Umklapp process, provides the missing angular momentum required for the Gaussian-beam scattering. Furthermore, we predict that as the degree of light focusing increases, the relative efficiencies of the Gaussian-beam and optical-vortex scattering processes reverse.

Perpendicularly magnetized magnetic tunnel junctions (MTJs) based on oxide materials are promising candidates for spintronic applications because of their high chemical stability and potential for high spin polarization. In this work, we investigated the spin-polarized electron tunneling through MgO (001) barriers from conductive Fe-rich cobalt ferrite CoyFe3-yO4 (C-CFO) (001) layers, where the conductivity is caused by electron hopping between Fe2+ and Fe3+ ions and the films exhibit perpendicular magnetic anisotropy. Perpendicularly magnetized C-CFO/MgO/C-CFO MTJs, composed of lower and upper C-CFO electrodes serving as a spin injector and a spin detector, exhibited clear tunneling magnetoresistance (TMR) effect and a spin injection efficiency of -14.2% at 150 K. The bias-voltage dependence of the TMR ratio is considerably smaller than that reported for conventional oxide-based MTJs. These results demonstrate that C-CFO can function as an electrode material in perpendicularly magnetized MTJs and exhibits relatively weak bias dependence compared with previously reported oxide-based systems.

Orbital currents induced by electric fields in transition metals have been experimentally reported in various material systems to date, in the form of orbital torques and orbital accumulation. However, most of these studies have been conducted on polycrystalline systems, and there has been virtually no discussion on their relation to first-principles electronic band structure calculations. In this study, we investigated the orbital Hall effect using epitaxial thin films of Ti, a 3d transition metal in which the spin Hall effect is negligibly small and the orbital Hall effect is dominant. Our first-principles calculations revealed that, within the Ti(1100) plane, the magnitude of the orbital Hall conductivity differs depending on whether the electric field is applied along the [0001] or [1120] direction. Based on this, we fabricated epitaxial Ti(1100) films and detected orbital torque using Ni, which has negligible magnetocrystalline anisotropy. As a result, we observed a clear anisotropy in the orbital torque generation efficiency depending on the direction of the applied electric field, consistent with the calculations. Furthermore, when using this orbital torque to reverse the magnetization of Ni, we found that the critical current density required for magnetization switching also varied according to the magnitude of the orbital torque generation efficiency. In this way, our study discusses the anisotropy of the orbital Hall effect in epitaxial transition metals with an aspect not observed in previously reported polycrystalline systems and offers a new direction in research on the orbital Hall effect.

Yttrium iron garnet (YIG) is known for its extremely low magnetic damping, making it a key material for magnon-based spintronic devices. Although perpendicular magnetic anisotropy (PMA) has been reported in rare-earth-substituted or Bi-doped YIG thin films, its realization in pure YIG remains limited. In this work, we demonstrate that YIG thin films grown on the substituted gadolinium gallium garnet substrates exhibit PMA and a low damping constant. X-ray diffraction measurements revealed an in-plane tensile strain relative to bulk YIG, suggesting that the strain-induced lattice distortion plays an important role in the emergence of PMA. Spin-wave propagation with a forward-volume configuration is investigated using two separated coplanar waveguides and a network analyzer. The measured propagating spin-wave spectra show a coherent propagation over several micrometers with a group velocity of approximately 0.2 km/s. Furthermore, in a heterostructure with a heavy metal layer of Pt, current-induced spin-orbit torque successfully switches the perpendicular magnetization. These results establish sputter-deposited YIG thin films with perpendicular magnetization as a promising platform for studying low-damping spin-wave transport and current-driven magnetization dynamics.

The transition from planar to three-dimensional (3D) magnetic nanostructures represents a significant advancement in both fundamental research and practical applications, offering vast potential for next-generation technologies like ultrahigh-density storage, memory, logic, and neuromorphic computing. Despite being a relatively new field, the emergence of 3D nanomagnetism presents numerous opportunities for innovation, prompting the creation of a comprehensive roadmap by leading international researchers. This roadmap aims to facilitate collaboration and interdisciplinary dialogue to address challenges in materials science, physics, engineering, and computing. The roadmap comprises eighteen sections, roughly divided into three blocks. The first block explores the fundamentals of 3D nanomagnetism, focusing on recent trends in fabrication techniques and imaging methods crucial for understanding complex spin textures, curved surfaces, and small-scale interactions. Techniques such as two-photon lithography and focused electron beam-induced deposition enable the creation of intricate 3D architectures, while advanced imaging methods like electron holography and synchrotron x-ray tomography provide nanoscale spatial resolution for studying magnetization dynamics in three dimensions. Various 3D magnetic systems, including coupled multilayer systems, artificial spin-ice, magneto-plasmonic systems, topological spin textures, and molecular magnets are discussed. The second block introduces analytical and numerical methods for investigating 3D nanomagnetic structures and curvilinear systems, highlighting geometrically curved architectures, interconnected nanowire systems, and other complex geometries. Finite element methods are emphasized for capturing complex geometries, along with direct frequency domain solutions for addressing magnonic problems. The final block focuses on 3D magnonic crystals and networks, exploring their fundamental properties and potential applications in magnonic circuits, memory, and spintronics. Computational approaches using 3D nanomagnetic systems and complex topological textures in 3D spintronics are highlighted for their potential to enable faster and more energy-efficient computing.

In this study, we investigated the nonlinear response of hybrid magnons consisting of acoustic and optic magnon modes in in-plane magnetized synthetic antiferromagnets. Using the heterodyne magneto-optical Kerr effect technique, we optically measured the properties of hybrid magnons under various excitation powers. These measurements revealed that the increase in the excitation power changed the resonance spectrum and the intensity distribution of the magnon dispersion relation due to the nonlinear dynamics of propagating magnons. This study advances the understanding of the nonlinear behavior of hybrid magnons, contributing to the future development of magnonic logic circuits and quantum devices.

The anomalous Nernst effect (ANE) generates electromotive forces transverse to temperature gradients and has attracted much attention for potential applications into alternative thermoelectric power generators. ANE efficiency is generally characterized by uniform temperature gradients in a steady state prepared by heaters. However, although focusing laser beams on a magnetic film can form much larger temperature gradients, the laser-irradiation method has not been sufficiently considered for quantifying the ANE coefficient due to the difficulty in estimating the localized in-homogeneous temperature gradients. In this study, we present a quantitative study of ANE in Ru(5 nm)/Co(t_Co) (t_Co = 3, 5, 7, 10, 20, 40, and 60 nm) bilayers on sapphire (0001) substrates by combining a laser irradiation approach with finite-element analysis of temperature gradients under laser excitation. We find that the estimated ANE coefficients are consistent with previously reported values and one independently characterized using a heater. Our results also reveal the advantages of the laser irradiation method over the conventional method using heaters. Intensity-modulated laser beams can create ac temperature gradients as large as approximately 10^3 K/mm at a frequency of tens of kilohertz in a micrometer-scale region.

The practical difficulty in distinguishing the impact of magnetic circular dichroism and the inverse Faraday effect fuels intense debates over which mechanism predominantly drives the process of helicity dependent all-optical switching of magnetization in ferromagnets. Here, we quantitatively measure the efficiency of the switching process in a Pt/Co/Pt multilayered stack using visible- to near-infrared optical pulses. We find that the switching efficiency increases by a factor of 8.6 upon increasing the pumping wavelength from 0.5 $ \mu $m to 1.1 $ \mu $m, becoming 100 % efficient at even longer wavelengths up to 2.0 $ \mu $m. Our experimental results can be successfully explained by the phenomenon of magnetic circular dichroism, making a significant step towards resolving the long-standing controversy over the origin of the all-optical process of magnetization reversal in ferromagnets.

Current-induced switching of magnetic octupoles in noncollinear antiferromagnetic (AFM) Mn3Sn has gained much interest in the development of fast and energy-efficient magnetic memory devices. Though full switching of Mn3Sn AFM order has been achieved in the epitaxial film prepared by molecular beam epitaxy, the switching rate (ξ) of sputtered Mn3Sn films has been mostly limited to 40% due to crystalline imperfections. Herein, our study reports how the Mn-deficiency affects SOT switching behavior. We find that controlling Mn composition through the co-sputtering method not only eliminates secondary phases and stabilizes the Mn3Sn phase but also naturally controls the interfacial conditions in the sputtered W/Mn3Sn bilayers. These improvements lead to coherent crystallinity with an atomically sharper interface, resulting in 100% switching of the magnetic cluster octupole of Mn3Sn. Our findings provide ways for optimizing the spin-orbit torque switching efficiency of Mn3Sn-based devices.

Topological superconductors are one of the intriguing material groups from the viewpoint of not only condensed matter physics but also industrial applications such as quantum computers based on Majorana fermion. For real applications, developments of thin-film topological superconductors are highly desirable. Bi/Ni bilayer is a possible candidate for thin-film chiral superconductors where the time-reversal symmetry is broken. Here we report the phase shift of resistance oscillations by half flux quantum in a ring-shaped device of epitaxial Bi/Ni bilayer induced by a small magnetic field through the ring. The half quantum fluxoid can be decisive evidence for unconventional superconductors where the superconducting order parameter has an internal degree of freedom. The present result provides a functional operating principle for quantum devices where the phase of the supercurrent can be shifted by [Formula: see text] with a small magnetic field, based on the internal degree of freedom had by topological superconductivity.

Ultrafast dynamics of magnetic properties in the high gigahertz (GHz) or even terahertz (THz) frequency range may be exploited in next-generation data storage and processing devices, and therefore suitable methods for detecting ultrafast dynamics of magnetization need to be developed. In this work, we investigate the impact of optically induced ultrafast precession of magnetization on the anomalous Hall conductivity in a ferromagnetic Co − Pt multilayer structure using THz-based pump-probe measurements. From the measured Faraday rotation, the time-dependent anomalous Hall conductivity σ x y is extracted, and our data reveals an initial ultrafast quench due to laser-induced demagnetization and a subsequent oscillation with a frequency that increases with the strength of the applied external magnetic field H ext . for H ext = 30 kOe, the oscillation frequency reaches approximately 100 GHz. The magnetic-field dependence of the oscillation frequency is in good agreement with the prediction from the ferromagnetic resonance model, confirming that the observed oscillation is caused by coherent magnetization precession. These findings are considered to be useful for studies that aim to integrate spintronics and THz electronics.

We demonstrate the epitaxial growth of NiAs-type CrSb thin films on LaAlO3(110) and Al2O3(1120) substrates via magnetron cosputtering, aiming to establish a platform for altermagnetism studies. Two distinct orientations-CrSb(1100) and CrSb(1120)-were realized by optimizing lattice matching and applying a W(110) buffer layer when necessary. X-ray diffraction and scanning tunneling electron microscopy (STEM) analyses confirm high crystallinity, with temperature and preannealing conditions found to critically affect film quality and phase formation. A coexistence of (1100) and (0001) phases was observed at elevated temperatures, accompanied by improved mosaicity. Nanobeam diffraction reveals local grain structures, while EDS confirms the near-stoichiometric composition. The hysteresis loop measurements reveal weak ferromagnetic-like signals, likely originating from interfacial defects, while no anomalous signals are observed. The minimal buffer layer requirement on insulating substrates makes the films compatible with advanced characterizations such as magnetotransport and ARPES. We believe our results offer new insight into the growth behavior of CrSb and provide a foundation for future experimental exploration of the altermagnetic materials.

Light possesses both spin and orbital angular momentum. In spatially asymmetric optical fields, these properties undergo spontaneous coupling, referred to as optical spin-orbit coupling. The study of the coupling has recently become central in modern optics due to its substantial applications in communications, sensing, and quantum control. A key challenge is to clarify the relationship between the origins of spatially asymmetric optical fields and the resulting spin-orbit coupling. Current research focuses on materials and configurations exhibiting spatial asymmetry, such as focusing lenses, interfaces, inhomogeneous media, and metasurfaces. However, Maxwell's equations indicate that matter can introduce both spatial and temporal asymmetry into optical fields. For instance, magnetic ordering breaks the time-reversal symmetry of interacting optical fields via the magneto-optical effect, introducing nonreciprocity in the resulting optical phenomena. Despite the importance, optical phenomena involving both spatially and temporally asymmetric optical fields remain unexplored. Here, we demonstrate that breaking time and spatial symmetries through magnons and light focusing, respectively, transforms an input Gaussian beam into a specific optical vortex beam in a nonreciprocal manner. This phenomenon is quantitatively explained by integrating the physics of magnon-induced Brillouin light scattering with optical spin-orbit coupling. The observed conservation of total angular momentum, encompassing both magnons and photons, further indicates that magnons can control both spin and orbital angular momentum of light. Finally, we outline future research directions enabled by asymmetric optical fields in both space and time.