Critical exponents and domain structures of magnetic semiconductor EuS and Gd-doped EuS films near Curie temperature

Critical behavior near ferromagnetic transition in EuS and Gd-doped EuS films was studied by magnetization measurement and cryogenic Lorentz microscopy. Ferromagnetic s–f interaction was strongly enhanced by doping 2% Gd. The Curie temperature and critical exponents of the magnetic phase transition for Gd-doped EuS were determined to be 86.3 ± 0.2 K, β = 0.43 ± 0.01, and γ = 1.20 ± 0.05 from the scaling plot, while those for EuS were 14.6 ± 0.1 K, β = 0.39 ± 0.01, and γ = 1.20 ± 0.05. The different universality classes of these materials showed different magnetic domain structures near the Curie temperature: the long-range ferromagnetic ordering based on the mean field model causes the formation of a large domain.