For pure erbium, the saturation moment along the c-axis was found to be 276.0±2.0 emu/g. by fitting the data to a T3 plot and extrapolating to 0°K. This is to be compared with a theoretical value of 300.5 emu/g. The discrepancy between experiment and theory is apparently the result of a ferro¬magnetic spiral arrangement of spins where the spins are cocked at an angle to the c-axis rather than being aligned parallel to it. Curie and Neel temperatures were found at 18.2±0.5 and 86.5±0.5°K respectively. Peaks in the c-axis moment vs. temperature curves were also observed which extra¬polated to zero-field temperatures of 28.0±0.5 and 50.5±0.5°K. The latter corresponds to the transition from one antiferro-magnetic structure to another while the significance of the former is unknown. Peaks occurred in both the a- and b-axis moment vs. temperature curves below about 18.5 K-Oe. Below about 10 K-Oe., the temperature of the peaks was field independent and occurred at about 18.2°K. In both the a- and b-axis moment vs. field curves, there were discontinuous in¬creases in moment at about 18.5 K-Oe. near 4.2°K. These apparently correspond to a sudden transition to a nearly parallel alignment of spins at an angle of about 23° to the axis. Some very small basal-plane anisotropy was observed below 40°K. At 4.2°K, the b-axis moment was about 2% larger at high fields.
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