"Version: 20240201"--Title page verso.Includes bibliographical references.1. Introduction -- 1.1. Origin of magnetic moment -- 1.2. Magnetic properties of materials -- 1.3. Magnetic domain wall dynamics -- 1.4. Spintronics applications of ferrimagnet -- 1.5. Theory of current-induced DW motion -- 1.6. Features of Mn4N2. Research history of Mn4N-based mixed crystals : several research topics -- …