Padé Approximant Estimates of the Magnetic Properties of EuO and EuS

Abstract

A Padé approximant analysis has been made of the magnetic susceptibility (X) and magnetic specific heat (C_m) of EuS. A similar, less detailed, calculation has been made on EuO. All calculations are limited in accuracy because only a few terms are known in the appropriate power series. Our calculations indicate that the Curie temperature (T_c) for EuS appears to be in the range 14.5°–16.0°K with γ≃1.4, where γ is defined by X→(T‐T_c)^−γ as T→T_c⁺). T_c for EuO appears to be in the range 60°–70°K with γ≃1.4. In our calculations for EuS, the exchange integrals of Charap and Boyd (J₁/k=0.20°K and J₂/k=−0.08°K) were used. For EuO, the exchange integrals J₁/k=0.65°K and J₂/k=−0.05°K were used. Our results indicate that the exchange integrals of Charap and Boyd can be improved upon. In particular, the set proposed by Passenheim et al. (J₁/k=0.20°K and J₂/k=−0.06°K) appears to be better. Similar comments are true for EuO. It appears that the Curie temperature predicted by the Padé approximant method provide at least one rather sensitive test for any proposed set of two exchange integrals.