This review aims a brief and short-handed overview on altermagnetism, a new magnetic phase recently proposed. The altermagnetism is mostly regarded as d-wave magnetism, as a counterpart of d-wave superconductivity. Hence, short-handed summary on d-wave superconductivity in terms of gap symmetry is provided. As symmetry arguments are unavoidable in discussing altermagnetism, operators consisting of groups, more specifically spage group and spin group, are introduced. As final remark, the comparison between antiferromagentism and altermagnetism is outlined.

Spin waves, or magnons, are waves resulting from the disturbance of spin alignment in magnetic materials. When magnons propagate within a solid, the absence of moving parts is believed to lead to smaller heat dissipation. This review introduces experimental methods for generating and measuring propagating magnons in magnetic materials using ultrafast laser pulses. Modern ultrafast lasers typically feature short pulse widths of 100 femtoseconds, enabling a wide bandwidth ranging from gigahertz to terahertz frequencies. In this scenario, optically generated magnons exhibit much longer wavelengths than the lattice parameters of solids, underscoring the crucial role of long-range interactions among magnetic dipoles in the dispersion relation near the Brillouin zone center. Such interactions manifest not only in ferromagnets but also in antiferromagnets, providing a foundational framework for investigating magnon transport and advancing the development of future magnonic devices.

In this paper, an efficient reliability analysis technique for the performance function of an electric motor is taking into account the insulation deterioration of stator windings as well as the uncertainty due to manufacturing tolerance. An insulation resistance formula is first derived to predict accurate insulation degradation over operating temperature and time, and then a precise numerical simulation model for a motor is constructed by utilizing the electromagnetic-thermal analysis tool linked to an equivalent circuit model. Based on the independence between probability design variables and time along with the simulation model, complex time-varying reliability analysis is converted into time-invariant reliability analysis. To examine the validity of the proposed method, the probability distribution and reliability of a performance function for an interior-type permanent magnet synchronous motor due to the manufacturing tolerance included in design variables are compared with and without consideration of insulation deterioration.

SRM is driven by a unidirectional excitation system and uses reluctance torque. Unlike permanent magnet AC motors that use mutual torque, SRM has a magnetic flux density as low as the magnetic flux created by permanent magnets. Recently, HRM (Hybrid Reluctance Motor), which increases torque density by increasing magnetic flux density by adding permanent magnets to the stator of SRM, has been studied. This paper presented the magnetic structure of a new TPHRM (Two Phase HRM) with a permanent magnet and U-core in the stator and compared and analyzed it with the TPSRM (Two Phase SRM) with self-starting capability. FLUX, a finite element method analysis program, was used for this magnetic analysis.

This paper presents the optimal design of a 15 kW permanent magnet synchronous motor for personal mobility using non-rare earth permanent magnets (PMs) as an alternative to neodymium PMs. The characteristics of neodymium permanent magnet motors are compared with those when replaced with ferrite permanent magnets, and methods for improvement are suggested. The electromagnetic performance according to the rotor outer diameter, the shape of the PM, and the number of layers of the PM are compared, and the initial design is carried out considering the irreversible reduction characteristics and mechanical stability. Considering that it is for personal mobility, the efficiency of the main operating points for urban driving is considered, and two-step optimization is performed to reduce the number of experimental points. Based on the optimal design results of this paper, the suitability of synchronous motors using rare earth permanent magnets for personal mobility is suggested.

The magneto-optic effect allows the optical detection of magnetization. The optical detection has advantages of non-contact, spatial resolution, time resolution, and high sensitivity. In this review article, I will introduce the optical method for spintronics research in three topics. First, using the optical method, spin-orbit torque in the non-magnet/ferromagnet bilayer can be measured. Especially, the optical detection of spin-orbit torque has certain merits compared to the electrical detection. Second, using the optical method, spin polarization in the non-magnet single layer can be measured. Especially, the spatial and time resolved detection provides strong evidence for the spin generation mechanism. Third, using the optical method, orbital polarization in the non-magnet single layer can be measured. Especially, the orbital sensitivity that depends on materials is the key feature for the optical detection.

This paper present a principle of defect detection in Magnetic Eddy Current Testing (MEC) for ferromagnetic pipeline inspection. The existing methods used in pipe inspection have their own limitations. Conventional eddy current testing (ECT) is unable to detect defects that is located in opposite-side due to limitations of penetration depth. And Magnetic Flux Leakage Testing (MFL) can detect both side defects, but it cannot distinguish between them. MEC can overcome the limitations of conventional methods. It can detect opposite-side defects and distinguish between surface defect and opposite-side defect. When a DC magnetic field is applied to pipe, permeability perturbation around defects occur due to field saturation so that it enables to detect opposite-side defects. Additionally, surface defects and opposite-side defects can be distinguished through the phase difference of the coil voltage signal. In this paper, When opposite-side defects exists in the pipe, the permeability distribution around the defect was analyzed, and the fluctuation of impedance in the coil due to the defect was studied. Next, experiment was performed. the result shows that MEC can detect oppositeside defects well and distinguishing between surface defects and opposite-side defects through the phase of the signal.

In this study, the test specimen was produced with surface flaws of different depths machined into SM20C magnetic material. The flaws were scanned using a magnetoresistive sensor that measures the magnetic field in the horizontal direction, and the driving frequency dependence of the flaw signal was analyzed. The flaw signal measured at a low driving frequencies showed a nearly constant value with the frequency, which was found to be a magnetic field distribution caused by magnetic poles induced on the surface by flaws in the magnetic material. While, at high driving frequencies, the flaw signal characteristics due to typical eddy currents were linearly proportional to the depth of the flaw and proportional to f^1/2 with driving frequency.

Magnon-photon coupling has been studied to develop effective quantum transducers and long-lifetime quantum memories. In order to achieve magnon-photon coupling, various cavity structures and magnetic materials have been used to excite a photon and magnon of a certain frequency. However, most of the studies so far have remained in the gigahertz (GHz) frequency range, so it is hard to achieve magnon-photon coupling in the terahertz (THz) range which is one of the efficient ways to make a high-temperature quantum regime. Here, we investigate the geometry optimization of a simple cavity structure, a split ring resonator (SRR) in the terahertz frequency range by using simulation as well as the experiment. The simulation shows that the efficiency and resonance frequency are varied by adjusting the geometric length and gap of the SRR. The simulation results are confirmed experimentally by using terahertz time-domain spectroscopy. This work paves the way for a controllability of terahertz photon resonator with high efficiency for high temperature quantum magnon-photon coupling experiments.

Distinction of spin angular momentum phenomena is one of the most important issues in orbitronics. Recent theoretical developments highlight a novel degree of freedom known as orbital angular position, capable of exhibiting phenomena not achievable solely through the spin degree of freedom. In this review article, we provide a mathematical demonstration of why such a degree of freedom should exist and summarize its consequences in both equilibrium and non-equilibrium condensed matter systems. Our work aims to assist future theoretical and experimental studies in understanding orbital angular momentum.

Very recently, THz emission and its application for THz spintronics has attracted much attention. In this review paper, universally observed THz emission generated by ultrafast demagnetization/remagnetization is introduced for representative 3d transition metal ferromagnets such as Fe, Ni, and Co films. Mostly, THz emission from relatively thick 30-nm films have been investigated to minimize the spin-charge conversion effect existing at the interface between ferromagnetic and nonmagnetic layers, with variation of external magnetic fields, laser pump fluences, and protection layers.