Anomalous pressure effect on the superconducting transition temperatures and critical fields of Ho1−xYxNi2B2C

The superconducting transition temperatures TC and upper critical fields HC2 of borocarbides Ho1−xYxNi2B2C have been measured under high pressure up to 3 GPa. It is found that TC of these compounds decreases with increasing pressure but the pressure derivatives have a maximum near x = 0.7,where the magnetic ordering temperature TN becomes 0. The pressure coefficients of HC2 show also a maximum near x=0.7. The possible origins of these anomalies are briefly discussed in connection with the instability of antiferromagnetism.