Multiple chiral magnetic domain walls (DW) motions on a perpendicularly magnetized nanowire by applying transverse magnetic field pulses are systematically investigated. The chiral DW motions depend on the directions of the magnetic fields, the magnetic domain wall configurations, and the signs of the Dzyaloshinskii-Moriya (DMI) interaction. For racetrack memory, the successive chiral DW motions by introducing the repetitive magnetic field pulses for both directions are numerically demonstrated. Lastly, various applications such as the next-generation non-volatile memory devices and the artificial intelligent logic devices based on the chiral DW motions are discussed.

We performed micromagnetic simulations on a multiple magnetic domain wall injector in a two-terminal device where a magnetic gradient is implanted at one end. In the magnetic gradient region, successive up-down magnetization is generated by the spin-orbit torque and, in turn, injected into the magnetic wire with a strong perpendicular magnetic anisotropy, resulting in multiple domain propagation. We found that the threshold current for the multiple domain injection is minimized when an effective magnetic anisotropy at the end becomes nearly zero. As the effective anisotropy becomes more negative, the threshold current increases with a magnetic anisotropy gradient because the gradient acts as a barrier to the domain injection. Our result provides design rules for the optimized magnetic anisotropy gradient for the multiple domain generation and injection.

We propose a universal spintronic logic device based on the current-induced magnetic domain wall (DW) motion. The majority gating operation is demonstrated by micromagnetic simulation using spin-orbit torque (SOT)-driven DW motion in Hall bar structures with perpendicular magnetic anisotropy. The logic gates including AND, OR, NAND, NOR are demonstrated, indicating the universality of DW majority gate. The simulation is partially confirmed by experiment, in which we found that the asymmetry in DW motion induced by Dzyaloshinskii-Moriya interaction or local Oersted field can cause the device malfunction. Our result suggests that the DW motion can be used not only in memory device but also in logic device, which could be useful in future processing-in-memory computing technology.

When studying magnetization dynamics, the model assuming that all magnetization vectors are aligned is called a macrospin model. The macrospin model has been considered as a most convenient method to solve the magnetization dynamics. The conventional method of obtaining a phase diagram of macrospin is to perform individual simulations on various variables and then combine all the results. This requires a lot of time and effort. Here, we introduce a method that can confirm the dynamic characteristics of macrospin for various variable values at once through computational simulation. We present an example of obtaining a two-dimensional phase diagram of a macrospin to identify magnetization switching characteristics and presession conditions by spin torque.

The thickness dependent magnetic properties of Ni₈₁Fe₁₉ thin film are investigated using Brillouin light scattering and Vector network analyzer-ferromagnetic resonance. Ni₈₁Fe₁₉ thin films are fabricated by DC magnetron sputtering system as 15, 30, 50, 70 nm. The determined magnetic parameters are saturation magnetization (M_s), exchange stiffness constant (A_ex), and Gilbert damping constant (α). M_s values are slightly increased as increasing Ni₈₁Fe₁₉ thickness and decreased as increasing Ni₈₁Fe₁₉ thickness. A_ex values are almost identical value as 8.9 pJ/m, and α is decreased from 0.0113 ± 0.0001 to 0.0086 ± 0.0002 as increasing Ni₈₁Fe₁₉ thickness.

In this study, a method was developed to confirm the deposition reproducibility of the magnetic layer thickness through the magnetic domain wall velocity analysis in the perpendicular magnetic thin film. We analyzed the effect of magnetic layer thickness and magnetic anisotropy on the magnetic domain wall motion occurring in a perpendicular magnetic thin film composed of Pt/Co/Pt. It was confirmed that the creep scaling constant (α) changed rapidly in the thickness regime of the magnetic layer where perpendicular magnetic anisotropy was formed. Using this, it is possible to check the change of α with respect to the change in the thickness of the magnetic layer of several Å.

We built ultrafast Sagnac interferometer to simultaneously measure the lattice and the spin dynamics. Although the pump-probe magneto-optical Kerr effect (MOKE) instrument is most widely used in Femtomagnetism to measure reflectivity and Kerr responses, it is considerably hard to analyze fundamental interactions of electron-spin or lattice-spin due to the complex nature of the reflectivity. The ultrafast Sagnac interferometer has the great advantage of obtaining the real and imaginary parts of MOKE as well as the reflectivity and the lattice displacement at the same time. Therefore, through the rigorous investigation of temporal sequences of electron, lattice, and spin systems, we expect this instrument to play an leading role in unraveling interaction mechanisms between systems.

The average life expectancy of modern people is rapidly increasing due to the development of medicine. The shoulder thermotherapy device (STD) used as a home medical device is studied for the purpose of relieving muscle pain in the upper part of the human body. The peripheral blood flow velocity (PBFV) could be measured from the two waveforms obtained by simultaneously measuring the pulse waves obtained by using a Hall element clip-type pulsimeter in the radial artery of the wrist and a photo-plethysmography (PPG) in the finger. Two women in their 20s with normal blood pressure used the STD by twice per a week for 13 weeks and compared before, middle, and after treatment, the PBFV improved by 12% to 17%.

The multi-layer solenoid coil is one of the most important design component for efficient electro-mechanical energy conversion in electrical machines such as generators, motors and transformers. When the voltage and current are applied across the coil, a uniform magnetic field is generated inside the coil and that is proportional to the number of coil windings, and the high-density magnetic field generated by the coil can be converted to mechanical energy by applying the strong electromagnetic force to a ferromagnetic material. At this time, the interaction between the current and magnetic field of the solenoid coil generates a strong electromagnetic expansive force between each coil wire. In this paper, we proposed both the method and formula to calculate the electromagnetic expansion force acting on the multi-winding layer solenoid coil by using the energy transfer equation. When the current flows a solenoid coil, the expansion force is generated in the radial direction of the coil. The mathematical calculation results were verified by simulated ones.

An attempt was made to fabricate the sintered La-base M-type single phase ferrite magnet, which was known to be difficult to synthesize, by Na-dopping. La-base M-type single phase (LaNa)Fe_8-xCo_xO₁₉ sintered ferrite magnet was successfully fabricated by dopping and substituting with Na = 0.2 and Co = 0.1. For this sintered magnet, M-phase fraction decreased with increasing Co-substitution. (La_0.8Na_0.2)Fe_7.9Co_0.1O₁₉ sintered magnet has good magnetic properties; M_s = 4.7 kG, B_r = 4.59 kG, which is considered to be superior to commercial ferrite magnet.

Hydrogel is a three-dimensional network structure with good biocompatibility, many of which are biodegradable and non-toxic. Therefore, hydrogels are widely used in environmental engineering, biomedicine, and other fields. Smart hydrogel is a kind of hydrogel that can respond to external stimuli. According to the stimulus-response type, smart hydrogels can be divided into thermal, pH, electric field, magnetic field response smart hydrogels. Magnetically responsive smart hydrogel, which has fast response, little harm to the human body, and remote control, can be used in biomedical fields, such as targeted drug delivery, assisted diagnosis, tissue engineering, and magnetic hyperthermia. This article introduces the fabrication methods and application fields of magnetic hydrogels. In particular, we discussed the characteristics, applications, and future research prospects of self-responsive smart hydrogel micro/nanorobots.