ORIENTATION, TEMPERATURE, AND FREQUENCY-DEPENDENCE OF NONRESONANT MICROWAVE-ABSORPTION IN HTSC POWDERS

Hysteresis in the microwave-power absorption of HTSC powders was studied as a function of temperature (T), field-sweep amplitude (H(max)), and orientation between the dc field (H(dc)) and the wave vector of the microwaves (k). It was found that (i) the sizable low-temperature hysteresis effects occur only if H(dc) parallel-to k, (ii) the temperature and frequency dependence of the hysteresis is strongly affected by H(max), (iii) the high- and low-temperature virgin curves are quite different, and (iv) the minimum of the absorption signal increases with H(max) and T. The low-temperature hysteresis loops were found to be similar to loops obtained from nonlinear equations describing cusp catastrophes.