A high field electron spin resonance spectrometer operating at a 25-Tesla water-cooled resistive magnet

We present a brief review focusing on recent research progress in high-field electron spin resonance (ESR) spectrometer with a focus on the construction and application of a 25-Tesla high-field ESR system. The spectrometer is based on a water-cooled resistive magnet at the Steady High Magnetic Field Facility in Hefei, China. Sample temperatures can be regulated between 2 to 300 K using a 4 He variable-temperature insert cryostat. A broadband microwave source, covering a frequency range of 50 to 690 GHz is achieved through a series of multiplier chain amplifiers, and signal detection is performed using an InSb bolometer. Key components of the spectrometer, including the probe, waveguide, and LabVIEW-based data acquisition software, are also described. The system’s performance was evaluated using the standard sample 2,2-diphenyl-1-picrlyhydrazyl. The spectrometer was primarily designed to support external users in investigating spin systems under extreme conditions—such as observing antiferromagnetic resonance in spin-ordered phases or detecting resonance signals in systems with large zero-field splitting, which are typically inaccessible to conventional X-band spectrometers. To illustrate its applicability, representative examples from materials science and condensed matter physics are provided.