The demand for high-efficiency motor systems, which consist mainly of magnetic cores made of soft magnetic materials and inverters that use power semiconductors, is increasing annually. To improve the efficiency of the motor system further, it is important to understand the magnetic and iron loss properties of the magnetic material core when it is driven by an inverter. This study presents the following three research findings regarding the properties of magnetic materials under inverter excitation: (1) magnetic and iron loss properties of magnetic materials excited by inverters with different diode properties; (2) magnetic and iron loss properties of nanocrystalline ring cores under Si-IGBT and GaN-FET inverter excitation; and (3) magnetic and iron loss properties of magnetic materials for the distortion of the pulse voltage waveform.