Magnetostriction of Erbium Single Crystals

Abstract

The magnetostriction of Er single crystals has been measured from 300° to 4°K in applied fields up to 30 kOe. Standard strain gauge methods were used. The exchange magnetostriction which results from the application of a c axis field was determined in the quasiantiphase domain and modulated moment temperature region. Above the exchange critical field, the c axis expanded sharply, and the basal plane contracted isotropically. At 29°K, for example, the critical field was 5.5 kOe, and the c axis and a axis strains were 2.8×10−3 and −1.1×10−3, respectively. Below 20°K application of a field in the basal plane produced a sharp change in strain at 18 kOe. A maximum c axis strain of 1×10−3 was accompanied by a smaller nonisotropic contraction of the basal plane and a net increase in volume. Examination of the high-field dependence of the strain and magnetic moment data suggests that these results arise from a field-induced breakdown of the conical ferromagnetic structure into a conical fan state. The b axis strain was measured as a function of applied field angle, and from these data the second-order anisotropic basal plane magnetostriction constant was obtained. In accordance with theoretical predictions,1 negative values (e.g., −8.2×10−5 at 65°K) were found above 55°K. Below 18°K unexpectedly small and positive values (e.g., 7.2×10−4 at 4.7°K) were obtained, presumably due to the effects of the exchange magnetostriction. The temperature dependence of the a, b, and c axis strains in zero applied field and in a 30-kOe field was determined. The zero-field data show inflection points at the 85° and 55°K oscillatory magnetic state transitions and sharp discontinuities at the 18°K transition to the conical ferromagnetic state.