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Application of the thermal boson expansion to the Heisenberg ferromagnets EuO and EuS.

Authors: C. Fiolhais, M. Brajczewska and J. da Providência

Ref.: Physica 147B, 249-258 (1987)

Abstract: The method of thermal boson expansion [1] is extended to the Heinsenberg model with spins S> 1 and applied to the ferromagnetic insulators EuO and EuS. Taking in the momentum space an adequate cut-off, which is almost independent of the spin, a good guess of the critical temperature temperature is made. The temperature dependent renormalization factor for spin waves and the reduced magnetization are calculated for a fcc lattice with S = 7/2, providing a reasonable agreement with the experimental data available on EuO and EuS.