We report here an experimental scheme based on a magneto-optical Kerr effect microscope to measure asymmetric domain-wall (DW) speed induced by Dzyaloshinskii-Moriya (DM) interaction. In this scheme, the possible artifacts caused by the in- and out-of-plane electromagnets are analyzed and carefully removed. The present scheme is then applied to measure the asymmetric DW speed of two different Pt/Co/Pt magnetic films with different magnetic layer thicknesses. In thinner magnetic film, the DW speed is well characterized by the DW energy variation model, enabling us to determine the magnitude of the effective in-plane magnetic field induced by the DM interaction. On the other hand, in the thicker film, the DW speed shows additional asymmetry, which is possibly caused by the variation of physical parameters other than the DW energy.

In this study, We employed Villari effect of ferro-magnetic materials i.e., magnetic properties change on mechanical stress, to develop nondestructive testing of tendons in bridges. To magnetize tendons, we constructed yoke with non-oriented Si-steel with 0.5 mm thickness sheet were laminated and 900 turns of enamelled Cu wire wound on the yoke. To measure magnetic induction and magnetic potential, 10 turns B-Coil and 3225 turns H-Coil were used. Diameter 15.2 mm, 15 numbers of 7 wire strand, was used as test tendon, and tension was applied to 7 wire strand up to 1300 MPa. Peak voltages induced from B-coil decreased linearly as tension increased. Peak voltages induced from B-coil were increased when we applied magnetic potential increased from 3600 Aturns to 7200 Aturns. Loss of cross sectional area of tendon can be measured using both B-coil and H-coil with sensitivity down to 3% loss of the cross sectional area.

The exchange stiffness constant A_ex was linearly propositional to the difference of spin wave resonance field H_SWR and ferromagnetic resonance field H_FMR. In this work, we measured the H_SWR and H_FMR with in-plane angles in order to analyze the angular dependence of A_ex in NiFe thin film with thickness of 100 nm. The A_ex of NiFe thin film was shown isotropic behavior not depending on the in-plane angles. The measured value of A_ex was 10.9 × 10⁻⁷ erg/cm and its value should be applied to the spin wave devices.

We have investigated magneto-transport properties in a MoS₂ lateral spin-valve structures for different ferromagnetic CoFe electrode shapes and MoS₂ channel lengths. For these devices, high quality and large-scale MoS₂ thin films were synthesized through sulfurization of epitaxial MoO₃ films and these sulfurized-MoO₃ thin films properties are in good agreements with measurements on exfoliated MoS₂ film. Magneto-transport measurements show a clear rectangular magnetoresistance signal of 0.16% and a spin polarization of 0.00012%. By using the one-dimensional spin diffusion equation, we extracted the spin diffusion length and coefficient, finding them to be 12 nm and 1.44 × 10⁻³ cm²/s, respectively. These small values of magnetoresistance and spin polarization could be enhanced by appeasement of conductivity mismatch between the ferromagnet and semiconductor interface.

We present a concise method to understand electric field response of electrons in the presence of spin-momentum coupling for a general two-band model. When there is no impurity scattering, the electric field response is solely described by the change of electronic wavefunctions since the electronic occupation remains unchanged. We found that this can be neatly described by a unitary transformation, which depends on both momentum and spin. Thus, it gives rise to gauge structures for both position and spin operators, which allows one to understand spin-orbit torque and anomalous Hall effect as consequences of the spin and position gauge effects, and spin Hall effect as a combined consequence of the two. As an example, we present a result for a model system with both Rashba interaction and s-d exchange interaction, which is a commonly used model to describe a thin magnetic layer.

This review aims a brief and short-handed introduction to nonexperts, where most contents are based on talk given in Summer School 2017 in Pohang. Detailed derivations and formalism are avoided unless it is necessary to present. Historical evolution of density functional theory (DFT) is provided to grasp the main motivation of first-principles calculations in a more broad perspective. By doing so, a list of acronyms is shown, which in many cases become an obstacle to newcomers. Furthermore, a classification of DFT packages according to vendors, methods, and others is provided for better understanding. Next, the practical employment of ab initio calculations in magnetism is introduced, which includes spintronics, for more specifically, spin and anomalous Hall effect (SHE and AHE), magnetocrystalline anisotropy (MCA), magneto-optical Kerr effect (MOKE). Also, ingredients for DFT calculations - human, package, and infrastructure (cluster or supercomputing center) are briefly outlined. To do so, we expect long-term improvement and investment in our field, which in turn help other expertises.

THz technique, which is considered to have great potential in exploring fundamental magnetic properties, is briefly reviewed with a special focus on metallic ferromagnetic film samples. Although numerous works have been carried out for semiconductor or insulator materials, only recently a few studies have been devoted to THz study of metallic ferromagnetic film systems. THz investigation related with magnetotransport and Gilbert damping parameter is introduced.