Magnetostrictive effects at a spin reorientation transition in a cubic crystal

Abstract

Mössbauer studies of spin reorientation transitions in the high magnetostrictive materials RFe 2( R = rare earth) were performed. The transitions studied were [100] → [110] (Ho 0.9Tb 0.1Fe 2 at 240 K), [100] → [111] (Dy 0.7Tb 0.3Fe 2 at 220 K), [110] → [100] (Ho 0.5Er 0.5Fe 2 at 135 K and Ho 0.3Tm 0.7Fe 2 at 110 K), [111] → [100] (Dy 0.2Er 0.8Fe 2 at 140 K) and [110] → [111] (Ho 0.7Tb 0.3Fe 2 at 120 K). The first four transitions were found to be of second order, continuous reorientation of magnetization. In Dy 0.2Er 0.8Fe 2 and Ho 0.7Tb 0.3Fe 2 a sharp discontinuous first order transition is observed. In all systems the Mössbauer recoil free fraction, its anisotropy, the isomer shift and hyperfine interaction parameters change sharply through the spin reorientation transition. All phenomena observed can be understood in terms of changes in static magnetostrictive distortions combined with critical phonon softening at the spin reorientation phase transitions. The system Ho 1- x Tb x Fe 2 is unique in behaviour as Ho 0.9Tb 0.1Fe 2 shows the highest magnetostrictive effects, whereas Ho 0.7 Tb 0.3Fe 2 shows almost none.