Magnetoelastic behaviour and the spin-reorientation transition in HoAl2

Abstract

The linear thermal expansion, AC susceptibility and magnetostriction have been measured on a single crystal of HoAl2. The authors' results clearly show two phase transitions associated, respectively, with establishment of magnetic order and with spontaneous spin reorientation. The critical exponent gamma SR of the susceptibility for T>or approximately=TSR has been determined. From magnetostriction measurements along the major symmetry directions of the crystal, they have obtained the possible deformation modes compatible with the point symmetry of the cubic crystal structure. A complete study of the magnetoelastic behaviour has allowed them to determine the reduced magnetoelastic coupling coefficients M2gamma /Cgamma , M2epsilon /Cepsilon , Mlalpha /Calpha (l=4,6) and Dalpha /Calpha . The model used is based on a single-ion origin for the crystal electric field interaction of the rare-earth ion, and they have taken into account the spontaneous reorientation of the magnetic moment in the molecular field, which represents the exchange interaction.