Thermal expansion and magnetostriction of single-crystal europium oxide

Abstract

Thermal expansivity and magnetostriction of an EuO single crystal were determined by using the strain gauge method in the temperature ranges 20°to 250°K and 4.2°to 150°K, respectively, and in magnetic fields up to 20 kOe. The magnetoelastic component of expansivity αme is observed to be proportional to the magnetic specific heat Cm. 1 As a result we obtain a temperature independent "magnetic" Grüneisen constant ∂ ln Um/∂ ln V=[minus]5.3 given by -3αmeCm-1B T using BT (isothermal bulk modulus) =1.07×10 12 dyn/cm2. For Um, the internal magnetic energy, we derive also the variation with temperature and magnetic field U m(T, H)/Um(0), the variation with pressure ∂ ln Um/∂ P=4.9×10-12 dyn-1cm 2, and the value Um(0) = -4.9×108 erg·cm-3 at 0°K. These results are obtained from treating various combinations of measurables including magnetization, isotropic forced magnetostriction, and zero-temperature volume anomaly as well as αme and Cm. The manner of suppression of the λ-transition by a magnetic field is also revealed by the data. Linear magnetostriction coefficients extrapolated to 0°K are λ 100=-22×10-6 and λ111= 55×10-6. Their decrease with increasing temperature is explained by a 1:1 admixture of single-ion and two-ion magnetoelastic coupling as described by λ(T)=·λ(0){Î5/2[L -1(m)]} and λ(T)=·λ(0)m2, respectively.2 © 1967 The American Institute of Physics.