Anomalous Thermal Expansion and Magnetostriction of Holmium Single Crystals

The a-, b-, and c-axis linear strains of single-crystal Ho have been measured from room temperature to 4^∘{}K in zero field and in applied fields up to 30 kOe. Pronounced bumps appeared in the thermal-expansion coefficient at the magnetic ordering temperatures of 132 and 20^∘{}K. The exchange magnetostriction contribution to the total c-axis strain was isolated and compared to the predictions of the molecular-field theory applied to spiral antiferromagnets. Strain data taken with an applied field show the effects of "fanning" of the moment about the applied-field direction and of the onset of basal-plane anisotropy below 75^∘{}K. The dependence of the basal-plane magnetostriction on field angle was measured in the temperature range of magnetic order. Saturation values of the second-order magnetostriction constant were compared with the results of single-ion magnetoelastic theory. A value of 2.5×{}10^-3 at T=0^∘K was calculated.