Abstract
Magnetostriction of single-crystal EuO was determined in the temperature range 4.2-150°K in applied magnetic fields up to 20 kOe. Linear magnetostriction coefficients extrapolated to 0°K are and . These yield the magnetoelastic coupling constants and dyn/. Their decrease with increasing temperature appears to be explained by a 1:1 admixture of longitudinal single-ion and two-ion spin correlation as described by and , respectively. This suggests that the magnetoelastic Hamiltonian contains one-ion () and two-ion () magnetoelastic constants, and . Since classical dipole-dipole interactions in EuO theoretically give and , we estimate for pseudodipolar effects and dyn/. The forced (volume) magnetostriction was obtained versus applied magnetic field and is plotted versus the internal magnetic field. These results, which reflect the behavior of short-range order (isotropic spin-spin correlations) in the presence of a magnetic field, are qualitatively similar to predictions of the two-particle cluster calculation by E. R. Callen and H. B. Callen. The Landau-Belov phenomenological theory, which is often used to estimate the pressure derivative of the transition temperature from data of versus , leads to results which are inconsistent with other determinations for in EuO and with the theoretical and experimental results in a previous paper, showing that EuO exhibits a temperature-independent magnetic Grüneisen parameter. Data exhibiting suppression of the anomaly in thermal expansivity by applied magnetic fields is also presented. The peak is rounded and its magnitude reduced by a factor of ≈½ at 18 kOe.
- Received 5 October 1967
DOI:https://doi.org/10.1103/PhysRev.171.555
©1968 American Physical Society