Magnetic resonance and cyclotron resonance of magnetic materials in millimeter and submillimeter wave region

Microwave spectroscopy of magnetic materials is a powerful tool to investigate their properties from a microscopic point of view. Especially, frequencies in millimeter and submillimeter region give many advantages for this purpose, although it is technically difficult to use these frequencies for real experiments. The author has been working on ESR experiments and developing sub-mm wave ESR equipment by use of FIR laser since the 1970s. It has been shown that the method of sweeping the magnetic field at constant frequency is much better than the usual spectroscopic method by an interferometer in the far infrared region, which had been the only way to observe ESR at such a high frequency before such experiments. Now frequencies up to 7 THz and magnetic fields up to 40 T are available at temperatures down to 0.4 K in our laboratory by using FIR laser, BTWT, Gunn oscillators and vector network analyzer.