Reentrant behaviour in Y-doped Ho0.75Y0.25Ni2B2C single crystal

The transport and superconducting properties of Ho0.75Y0.25Ni2B2C single crystals were investigated to study the competing effects between superconductivity and magnetism. The superconducting transition temperature Tc is 7.6 K, determined from the resistivity transition; meanwhile, the commensurate antiferromagnetic (AFM) transition occurs at TN of 3.9 K, which is lower than that of pure HoNi2B2C (TN∼5 K). Ho0.75Y0.25Ni2B2C reentered into the normal state at Tm (TN<Tm<Tc) when small magnetic fields were applied along the crystallographic c-axis. In contrast to the case in HoNi2B2C, the reentrant behaviour for Ho0.75Y0.25Ni2B2C only appears when the applied field H is along the c-axis, and the reentrant peak position TP(H) shifts to lower temperature with increasing applied field. We suggest that the disorder of magnetic structure induced by Y doping may account for the significant difference in the reentrant behaviour between Ho0.75Y0.25Ni2B2C and HoNi2B2C. Moreover, there does not exist a deep minimum in the upper critical field Hc2(T) line at TN of 3.9 K for either H parallel c or H perpendicular c. The H-T phase diagram is derived and discussed