A Sub-Kelvin Cryogen-Free EPR System

Abstract We present an EPR instrument built for operation at Q band below 1 K. Our cryogen-free Dewar integrates with a commercial electro-magnet and bridge. A description of the cryogenic and RF systems is given, along with the adaptations to the standard EPR experiment for operation at sub-Kelvin temperatures. As a first experiment, the EPR spectra of powdered Cr 12 O 9 (OH) 3 ( O 2 CCMe 3 ) 15 were measured. The sub-Kelvin EPR spectra agree well with predictions, and the performance of the sub-Kelvin system at 5 K is compared to that of a commercial spectrometer.