Chiral derivative is a useful tool to understand spin-orbit coupling effects in magnetic systems. In this review, we overview the derivation of the chiral derivative and discuss its applications for various situations such as Dzyaloshinskii-Moriya interaction, magnetic textures, and current-induced magnetization dynamics. Its generalizations for arbitrary linear spin-orbit coupling and magnon-driven magnetization dynamics are also discussed. Lastly, we review the limitations of the chiral derivative and present examples where the chiral derivative does not work properly.

Graphene is a two-dimensional material having the charge, spin and valley degree of freedom used for information transfer. For spintronics, graphene has emerged as a leading candidate for device applications due to high mobility and ultra-low spin orbit coupling. Also, graphene is an attractive 2D material for valleytronics because valley polarization can be induced by electrical or mechanical tuning. In this review, we focus on the spin and valley transport in graphene. The spin transport properties of graphene are usually studied with nonlocal spin valve devices because pure spin current can be injected into graphene and be detected as electrical voltage. The electrical generation of a spin current in graphene was tried using the spin Hall effect. The valley transport in graphene is also possible when the inversion symmetry of graphene is broken by applying gate voltage or using bi-layer graphene. From these transport properties in graphene, we briefly introduce the research trends of a spin relaxation mechanism, the spin Hall effect and the valley Hall effect in graphene for spintronics and valleytronics with their applications.

Magnetic skyrmion are an active research field in the rapid development owing to their potential for novel physics and applications of efficient next-generation spintronics device. In this work, we investigate the physical definition of skyrmions, and discuss skyrmion-based potential applications such as information storage, logic gates, neuromorphic devices, and non-conventional computing devices.

We analyzed the annealing temperature (T_a) dependence of exchange bias field (H_EB) in exchange coupled CoFe-MnIr thin films. The H_EB were increased up to T_a = 300 ℃ and then decreased at T_a < 300 ℃. The increase of H_EB at T_a < 300 ℃ was explained by the rearrangement of uncompensated spin by thermal activation. While, the decrease of H_EB at T_a > 300 ℃ was explained by the Mn interdiffusion. These thermal annealing effect contributed to the thermal stability of H_EB maintaining constant values up to annealing temperature.

The ferromagnetic resonance field and spin wave resonance field with in-plane angles Φ_H were measured in order to analyze the angular dependence of exchange stiffness constant A_ex in exchange biased MnIr/NiFe thin film. The A_ex of MnIr/NiFe thin film showed an anisotropic behavior such as A_ex = A₀ + A_ebcosΦ_H. The isotropic exchange stiffness constant A₀ was due to the exchange stiffness constant of NiFe, while anisotropic exchange stiffness constant A_eb was due to the exchange bias field.

In this article, the Permanent Magnet-Assisted Synchronous Reluctance Motor (PMa-SynRM) with application of grain-oriented electrical steel (GO) is proposed for electric vehicles (EVs). Because the GO has strong magnetic performance on the rolling direction, the GO is applied partially in the stator of PMa-SynRM. By applying GO, the performance at no-load condition and load condition are increased simultaneously. Especially, the average torque increased 3.24% and the iron loss at no-load condition and load condition decreased by 13.03% and 11.17%, respectively. Finally, by reducing the stack length in proportion to the increased torque, the iron loss at no-load condition decreased by 15.85%.

M-type hexaferrite (SrFe_9.6Co_1.25Ti_1.25O₁₉) powders having an electromagnetic (EM) wave absorbing capability at X-band (8~12 GHz) were dispersed with 2 wt% multi-walled carbon nanotubes (CNT) and rubber binder into a solvent to prepare a coating solution, and then composite films having a thickness of ~100 μm were coated on polyimide (PI) film using a coating applicator. After curing the sample at 80 ℃ for 10min, flexible hexaferrite-CNT-rubber composite films could be obtained. The X-ray diffraction analysis revealed that the ferrite particles in the composite film had randomly oriented single-phase M-type type hexagonal structure. Microstructure and thickness of the film were confirmed through scanning electron microscope (SEM) analysis. EM wave shielding and absorbing properties were measured by the S-parameter method using a network analyzer. A single layer of composite film (100 μm) exhibited a shielding effectiveness (SE) of -15 dB. A 1.7 mm-thick sheet laminated with the composite films exhibited a SE< -30 dB and a reflection loss (RL) of -7 dB at full X-band, which implies that it blocks more than 99.9% and absorbs ~90% of the incident EM wave energy. In addition, a SE of ~-70 dB could be achieved when a 12 μm-thick copper foil was attached to a single layer of composite film (100 μm).

This study was carried out to develop a new alloy superior to pure nickel powder used as a conductive powder material for a semiconductor test socket. As such means, composition variation of Fe-(3~70)wt%Cu binary system and Fe-Cu-X (X = Ag, Co, Sn) ternary system alloy, ingot manufacturing, thermal treatment, polishing, microstructure observation, and physical properties (electrical resistance, magnetism and hardness) were investigated. As a result, some of Fe-Cu binary alloys and Fe-Cu-X ternary system alloy had better properties than pure Ni. For example, in the Fe-(3~70)wt%Cu binary system alloy, the Fe-50wt%Cu alloy had electrical resistance (ρ) = 6.8 × 10^-8 Ω·cm, magnetism (Bs) = 0.9 (T) and hardness (Hv) = 209.8, which were superior to pure Ni. One of those reasons was estimated to be due to an increase in the volume fraction on the εCu (S.S.). In addition, in the case of Fe-Cu-X ternary system alloys, particularly, it was confirmed that the addition of Ag, Co, and Sn elements has a slight effect of increasing electrical resistance, but the magnetism (Bs) decreased as expected.

Cycloidal Reluctance Motor (CRM), called conventional wobble motor or cycloidal motor, shows a structure that can combine rotational and reciprocating motions such as a Crankshaft or Cam in the mechanical field. CRM differs from general motors in that the central axis of the motor and the central axis of the rotor are different, so the rotor is eccentric to the center of the stator. CRM has the advantage of having a large torque at low speed. This paper proposes a magnetic structure of a stator that can generate a larger torque in CRM. To verify the effectiveness of a given structure, the magnetic path was analyzed, the pole arc of the stator pole was changed or a flange was added to the stator pole. And the winding turns of stator were changed respectively. The efficacy of the magnetic analysis is validated using Altair FLUX, a finite element method program.