What is Multi-extreme THz ESR? Developments and its Applications

Abstract This review explores the multi-extreme THz ESR system in Kobe, Japan, with a focus on pulsed magnetic fields, mechanical detection, and high pressure as central elements of multi-extreme THz ESR. Initially, it discusses the advantages of multi-frequency THz ESR using mini-pulsed and 55 T‒pulsed magnetic fields, with typical examples featuring the finite Haldane chain substance Y 2 BaNi 0.96 Mg 0.04 O 5 and the deformed diamond chain antiferromagnet Cu 3 (CO 3 ) 2 (OH) 2 (Azurite). The measurement efficiency and the measurement beyond the magnetic phase transition, in contrast to the conventional superconducting magnet, are discussed. Second, the high sensitivity obtained from the use of a nano-membrane for mechanical detection is shown. Also shown are the high-temperature (280 K) THz ESR results for DPPH powder and a Cu(C 4 H 4 N 2 )(NO 3 ) 2 (CuPzN) single crystal, with the combination of a nano-membrane device and a high-power source, a gyrotron. Finally, the high-pressure THz ESR results for KCuCl 3 using a transmission-type double-layered pressure cell are shown, along with the application of the thermally detected high-pressure THz ESR.