The one-ion model and the magnetostriction of terbium and its gadolinium alloy

We measure the temperature dependence of the magnetostriction, the magnetostrictive contribution to the thermal expansion, and that of the magnetization of monocrystalline terbium and the alloy Tb_0,5Gd_0,5. We find that the experimental data agree with the predictions of the one-ion theory as regards the temperature dependence of the magnetostrictive contribution to the thermal expansion. We calculate from experimental data and thermodynamic relations the dependence of the transition temperature and the magnetic-crystalline interaction on the lattice parameters. We demonstrate the agreement of these relationships with estimates made according to the theory of the crystalline field using the one-ion model.