MICROWAVE MAGNETOABSORPTIONS OF YBA2CU3OY SINGLE-CRYSTAL

Microwave magnetoabsorption measurements were performed for a single c rystal of YBa2Cu3Oy in a temperature range from 3 to 150 K. The lower critical fields were determined as 450 +/- 10 and 150 +/- 10 Oe at 5 K for the c-axis and the ab plane, respectively. Their temperature vari ations were also investigated. ESR signals of Y2BaCuO5 precipitates we re observed even below the Neel point of 12 K, because superparamagnet ic properties appeared. A fluctuation-induced magnetization persisted above the superconducting critical temperature of 94 K in a temperatur e range up to 150 K. (C) 1997 Elsevier Science B.V.