Magnetic Equation of State in a Substitutionally Random Ferromagnet, Eu_xSr_1−xS

Abstract

Precise measurement of static magnetization in a weak external field was carried out for ferromagnetic solid solution, Eu_xSr_1−xS. It is shown experimentally that the situation near the transition point is unchanged by the dilution: the magnetization can be expressed only by the magnetic field if both quantities are scaled for temperature as m∝M·|(T⁄T_c)−1|^−β and h∝H·|(T⁄T_c)−1|^−βδ, respectively, provided that β_cal=γ⁄(δ−1) is used in the scaling instead of experimentally determined β. When x is larger than 0.85, β_cal coincides with β. β_cal is larger than β for x less than 0.85. In the latter case, above argument on the scaling does not hold in the immediate neighbourhood of the transition point, T=T_c, H=0. The boundary of the region is shown in the T-H plane where the scaled magnetic equation of state exists. Critical indices β, γ and δ, experimentally determined and used in the scaling, change appreciably with Eu concentration. Both γ⁻¹ and the ferromagnetic Curie point, T_c, have a same dependence on x.