Magnetostrictive effects at a spin reorientation transition in a cubic crystal

Mössbauer studies of spin reorientation transitions in the high magnetostrictive materials RFe₂(R = rareearth) were performed. The transitions studied were 100] → 110] (Ho_0.9Tb_0.1Fe₂ at 240 K), 100] → 111] (Dy_0.7Tb_0.3Fe₂ at 220 K), 110] → 100] (Ho_0.5Er_0.5Fe₂ at 135 K and Ho_0.3Tm_0.7Fe₂ at 110 K), 111] → 100] (Dy_0.2Er_0.8Fe₂ at 140 K) and 110] → 111] (Ho_0.7Tb_0.3Fe₂ at 120 K). The first four transitions were found to be of second order, continuous reorientation of magnetization. In Dy_0.2Er_0.8Fe₂ and Ho_0.7Tb_0.3Fe₂ 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-xTb_xFe₂ is unique in behaviour as Ho_0.9Tb_0.1Fe₂ shows the highest magnetostrictive effects, whereas Ho_0.7 Tb_0.3Fe₂ shows almost none.