Anomalous Thermal Expansion and Magnetostriction of Holmium Single Crystals

Abstract

The $a$-, $b$-, and $c$-axis linear strains of single-crystal Ho have been measured from room temperature to 4\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ at $T=0\ifmmode^\circ\else\textdegree\fi{}$K was calculated.