Magnetoelastic properties of rare-earth paramagnetic garnets: Magnetostriction and thermal expansion

Abstract

The differential longitudinal magnetostriction (MS), in fields up to 50 KOe, for the [111], [110] and [001] crystal axes at 4.2 K and the crystal lattice parameter between 5 and 290 K for garnets R 3Ga 5O 12 and R 3Al 5O 12 (R = GdYb) are measured. The MS for all garnets except GdGG is very anisotropic and does not saturate; its value and sign change in an irregular way throughout the series of rare-earth (RE) ions. Within the terms of the crystal-field model the quadrupole approximation for the magnetoelastic energy is discussed. For the garnet structure with inequivalent sites of RE ions, the MS is expressed in terms of the field-induced changes of quadrupole moments which are numerically calculated for the known crystal fields. Semiquantitative analysis of experimental data allows one to account for the variation of the sign and value of MS from one garnet to another. Anomalies of the crystal lattice parameter observed at low temperatures for some RE garnets are described.