The magnetic losses generated when an alternating magnetic field is applied to magnetic nanoparticles can be used as the heat required for cancer hyperthermia therapy. Furthermore, magnetic nanoparticles can be used in medical imaging for detecting the resulting changes in magnetization from outside the body. Many challenges must be overcome before these diagnostic and therapeutic methods can be used with humans, that is, in clinical practice. This article provides a detailed review of the magnetic properties of commercially available magnetic nanoparticles. We discuss measurement results for multicore particles, particle clusters with specific diameters, and the respective samples in which the easy axes of magnetization are aligned. This review provides fundamental insights into the key challenges in improving the heat generation of magnetic nanoparticles and the detection sensitivity in imaging.

  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.