MAGNETIC-PROPERTIES OF SINGLE-CRYSTAL GDNI2B2C

Single crystals of GdNi2B2C have been grown out of Ni2B flux at high temperatures. Temperature and field dependent magnetization measurements on these crystals show that in low fields (1 kG) there are two phase transitions: at 20 K there is a paramagnetic to antiferromagnetic phase transition and at 14 K there is another transition which we infer to be a spin reorientation transition. The lower temperature transition manifests itself clearly in the anisotropic magnetization data, but is effectively averaged out in measurements of a powdered sample as well as in the polycrystalline average of the anisotropic magnetization data. Both of these transitions are also conspicuous in the temperature dependent electrical resistivity. GdB2C2 single crystals were also grown out of Ni2B flux. This compound has an antiferromagnetic phase transition at 47 K and is very likely an impurity phase responsible for the earlier, spurious, report of a 45 K phase transition in GdNi2B2C.