Multi-frequency electron spin resonance apparatus in millimeter-wave range using a compact gyrotron

Abstract

Electron spin resonance (ESR) is widely used in science because it provides information on magnetic properties from a microscopic viewpoint. It is known that the ESR resolution improves as the light source becomes higher in frequency. The gyrotron is a kW-class high-power light source capable of oscillating in the THz-band. We have developed a highly sensitive magnetic resonance system by combining with a Force-Detection ESR (FDESR) system that measures minute magnetization changes. Here, we developed a new multi-frequency ESR system by combining a Compact Gyrotron (FU-CW CI) and the FDESR system with a variable temperature cryostat which can be used in the temperature range 5–300 K. Multi-frequency ESR signals of 1,1-diphenyl-2-picrylhydrazyl (DPPH) as standard samples were successfully detected at room temperature in the fundamental oscillation region of the gyrotron (108–206 GHz). The sensitivity was obtained to be in the order of 10¹² spins/G from the ESR measurement of Cu(C₄H₄N₂)(NO₃)₂ at room temperature. In addition, ESR signals of DPPH due to second harmonic waves (294–394 GHz) were successfully detected in the cryogenic region at 13 K. These results demonstrate the high compatibility of the gyrotron and FDESR system, as well as the ability to make comprehensive measurements in the region up to 0.4 THz. Recently, this magnetic resonance apparatus has been used to develop spintronics devices for thin-film antiferromagnetic materials. In the talk, examples of collaborative research using this light source will also be presented.