EPR AND MICROWAVE-ABSORPTION STUDIES IN A NEW CLASS OF SUPERCONDUCTORS - QUARTERNARY RARE-EARTH TRANSITION-METAL BOROCARBIDES YPD5B3C0.35 AND YNI2B2C

Microwave-absorption techniques have been used for investigating the s uperconducting behaviour of the recently discovered quaternary rare-ea rth transition metal borocarbide superconductors. The direct microwave absorption shows a steep drop at 23 K in YPd5B3C0.35. Besides the exp ected drop in microwave absorption observed in YNi2B2C at 15.5 K, ther e is another drop at approximately 23 K, the origin of which is not un derstood at present. We have estimated the value of the lower critical field H(cl) (approximately 20 G at 10 K) in the two cases from magnet ic-field-modulated low-field microwave-absorption measurements.