Magnetic Equations of State of Heisenberg Ferromagnets, EuS and Its Sr-Diluted Derivatives, in a High Field Region

Abstract

Magnetization, M, of EuS and Eu_1-xSr_xS (x≤ 0.4) was measuredbelow 90 K in an external magnetic field up to 150 kOe. It is shownthat M in the paramagnetic region is well expressed by a Brillouinfunction for S=7/2, with an effective field H+λ M. Even attemperatures below asymptotic Curie temperature, magnetizationapproaches the Brillouin function with increasing fieldstrength. Moreover, it is found that magnetization scaled by(T-T_c)^b can be expressed as a universal function of magneticfield scaled by (T-T_c)^b+c. Here, T_c is the ferromagneticCurie point. Scaling exponents, b and c, are very different from thosein the critical region. The exponent c is about 1.15 and independentof x whereas b is 0.14 for EuS and decreases rapidly with increasingx, proportionally to T_c.