Magnetization isotherms on ErNi2B2C, Er0.8Tb0.2Ni2B2C and Er0.8Lu0.2Ni2B2C single crystals

The magnetic and superconducting properties of ErNi2B2C, Er0.8Tb0.2Ni2B2C and Er0.8Lu0.2Ni2B2C single crystals have been studied by DC magnetization measurements. Those crystals were grown by a floating zone method. The superconducting transitions (TC) were observed at 8.9, 4.0 and 11.1 K in ErNi2B2C, Er0.8Tb0.2Ni2B2C and Er0.8Lu0.2Ni2B2C, respectively. The field dependence of magnetization in ErNi2B2C showed a drastic change from negative to positive just over HC1 (400 Oe) in increasing applied field at 1.8 K near the weak ferromagnetic transition. A double meta-magnetic transition at 11 and 19 kOe was also observed. Although the opposite effects on ErNi2B2C doped with magnetic Tb and non-magnetic Lu were expected, all such anomalies were absent in Er0.8Tb0.2Ni2B2C and Er0.8Lu0.2Ni2B2C