Two types of magnetoresistance (MR), i.e., tunnel magnetoresistance (TMR) and current perpendicular to plane giant magnetoresistance (CPP-GMR), are theoretically discussed for systems with half-metallic (HFM) Co-based full Heusler compounds. In TMR, the non-collinear spin structure at the Co₂MnSi(CMS)/MgO(001) interface that results from thermal spin fluctuations significantly reduced the TMR ratio at room temperature (RT). Enhancement of the exchange stiffness of CMS/MgO was essential to suppress the reduction in TMR at RT. Furthermore, it is proposed that inserting of a B2-CoFe layer between CMS and MgO is a promising way to enhance the interface exchange stiffness constant. In CPP-GMR, the interface spin asymmetry γ in the Valet-Fert model was essential to enhance GMR at RT, because the temperature dependence of γ in experiments was much larger than that of the bulk spin asymmetry β. I showed that the experimental CPP-GMR ratio increases with the decrease in the theoretical resistance-area product R_PA, which is roughly consistent with the R_P dependence of γ. This means that matching of the conductive channel between HMF and a non-magnetic metallic spacer is a key parameter to enhance γ. These findings will be very important for room temperature spintronics devices applied in future artificial intelligence hardware.

  Magnetic nanoparticles have been used in various biomedical applications. Among these, magnetic particle imaging and hyperthermia are considered clinically useful diagnostic and therapeutic methods, respectively. An alternating magnetic field is applied to the magnetic nanoparticles in these methods. The magnetization response of a magnetic nanoparticle is essential, and the dependence of its field intensity and frequency determines its diagnostic and therapeutic performance. This article reviews the fundamental issues of the magnetization process and magnetization relaxation of magnetic nanoparticles and presents our recent experimental results.

  Non-metallic materials, such as inorganic/organic semiconductors and topological quantum materials are now collecting significant attention in modern spintronics. The progress of the research field using the materials is quite rapid and tremendous amounts of significant studies have been published. In this review article, some important milestone works are introduced to enhance further acceleration of the research fields.

  In most magnetic devices with thin films, the magnetic properties are governed by not only the intrinsic properties but also the microstructure. To realize high performance in magnetic devices, understanding the correlation between magnetic properties and microstructure is important. In this study, the development of ferromagnetic thin films for high-density recording media and large output current perpendicular to plane giant magnetoresistance devices are reviewed. Based on the experimental data, the research direction for next-generation high-areal-density magnetic recording is discussed.

  This paper reviews the crystal structure and magnetic and magneto-optical properties of CoPt, MnPt₃, CrPt₃, MnAl and MnGa films with an ordered phase as well as dot patterns fabricated on these films. CoPt film grown on a MgO (111) substrate at 300°C had an L1₁ phase and exhibited a large perpendicular anisotropy. CrPt₃ films, which had a (111) orientation and L1₂ phase, showed a large perpendicular anisotropy due to the magneto-elastic effect. By utilizing the change from L1₂ to a disordered phase caused by low-dose Kr⁺ ion irradiation, dot patterns were prepared on CrPt₃ film with a flat surface. It was found that a CoGa buffer layer was effective at growing thinner L1₀ MnAl and MnGa films on a MgO (001) substrate while keeping a (001) orientation. In the case of fabricating MnGa on SiO₂/Si substrates, a buffer layer of CoGa/Cr/MgO/Cr/NiTa was necessary to grow L1₀ MnGa with a (001) orientation.

  Cr₂O₃ is a magnetoelectric antiferromagnet, and its antiferromagnetic domain state is controllable by the simultaneous application of magnetic and electric fields. In the 2000s, that is, more than 50 years since the discovery of the magnetoelectirc effect in Cr₂O₃, efforts were initiated apply this effect to engineering applications. In this article, we review the recent progress of the magnetoelectric control of the antiferromagnetic domain state and the related phenomena of Cr₂O₃, in particular, in an all-thin film system, an essential step to the application.

  The review covers the research and development of perpendicular media nanostructure focusing on the recording layer. The recording layer material includes the Co-alloys with hcp structure, the magnetic multilayers, and the alloys with ordered structures that have high magneto-crystalline anisotropies (K_u). The technologies of underlayer or interlayer for aligning the easy magnetization axis of magnetic crystal grain perpendicular to the film plane are briefly reviewed including the high K_u magnetic materials for future recording media.

  Observations of compositional and magnetization structures in sub-μm scale have played important roles in improving the recording layer. Typical data on these characteristics are explained in relation to the media structure improvements. Considering that high K_u magnetic materials will be employed in future recording media, basic experimental results related in controlling the easy magnetization axis and in keeping the surface flatness of L1₀-ordered magnetic materials are explained. Future possibilities for increasing the areal density beyond 1 Tb/in² by improving the magnetic material and the nanostructure of recording layer are also discussed.

  Various transition-metal magnetic materials have been investigated from basic and practical viewpoints. The concentration dependence of the Néel temperature T_N of Cr-based alloys is complicated. Cr-Si and Cr-Fe antiferromagnetic alloys show Invar characteristics in the ternary alloys. Fe-based amorphous alloys exhibit weak ferromagnetic properties, resulting in remarkable magnetovolume effects. The icosahedral quasicrystals containing Mn show a spin-glass behavior, in a similar manner as those of amorphous counterparts. Itinerant-electron metamagnetic transition occurs in La(Fe_xSi_1-x)₁₃, accompanied by many drastic change in magnetic and elastic properties. These drastic changes are practically useful in the field magnetic refrigeration and linear magnetostriction. The magnitude of T_N of Mn-based γ-phase is increased by addition of Ir, Ru, Rh and the spin structures change, depending on temperature and composition. Several kinds of L1₀-type Mn alloys have a high value of T_N with a large magnetocrystalline anisotropy. The shift of the exchange-bias field for the collinear spin structure in L1₀-type phase is induced by spin frustration. L2₁- and B2-type Co₂CrGa metallurgical stable alloys exhibit a high spin polarization. Several kinds of L2₁-type and B2-type alloys show a large ferromagnetic shape memory effect associated with twin-boundary motions.

  L1₀-type alloys and L2₁-type Heusler alloys are key materials for future spintronic and magnetic storage devices. L1₀-FePt with high uniaxial magnetic anisotropy is a promising material for ultrahigh density recording because of its high thermal stability of magnetization at a nanometer scale. Co-based Heusler alloys showing high spin polarization of conduction electrons enable us to enhance the magnetoresistance effect. In addition, utilizing the magnetization dynamics in these ordered alloys provides us with new paths in the development of spintronic and magnetic storage devices. In this review, we introduce the control of magnetization switching field for L1₀-FePt exchange-coupled with Ni₈₁Fe₁₉ by utilizing the spin waves in the bilayers, which will be useful for information writing. A nanometer-scaled rf oscillator is also introduced, in which the magnetization dynamics is excited by spin angular momentum transfer. We can improve both the rf output power and the oscillation quality simultaneously by using Co₂(Fe_0.4Mn_0.6)Si Heusler alloy.