EPR SPECTROMETRY OF HIGH-TEMPERATURE SUPERCONDUCTORS WITH TEMPERATURE-MODULATION-BASED THERMOREGULATION

A light-beam-assisted temperature-control system operating within a te mperature range from 77 to 180 K is developed for investigating the ab sorption of electromagnetic waves by high-temperature superconductors in the vicinity of superconducting transition with an EPR spectrometer . The advantage of this system is the feasibility of modulating the te mperature of a sample with a frequency of 80 Hz and amplitude of 10(-2 )-10(-1) K. The rms temperature instability over a 5-min time interval is within 0.06 K, the temperature gradient in a sample is similar to 0.01 K/mm for T similar to 90 K, and the system relaxation time is 1-1 0 s. The microwave absorption peaks in the vicinity of the superconduc ting transition of an YBa2Cu3O7-x, single crystal were first measured at the simultaneous application of magnetic and temperature modulation s.