Upper-critical-field anisotropy and magnetic phase diagram of HoNi2B2C

To study the influence of the magnetic structure in the electronic properties, resistivity measurements were performed on high-quality HoNi2B2C single-crystal samples as a function of temperature or magnetic field. The temperature range investigated reaches from the superconducting transition temperature T-c=8.85 K down to 50 mK. Magnetic fields up to 5 T have been applied along the [001], [100] and [110] directions, respectively. In addition to the temperature dependence of the upper critical field, anomalies in the normal state resistivity could be assigned to metamagnetic phase transitions. Both the superconducting-normal and the magnetic phase diagram show large anisotropies.