The magnetic phase transition in the metal-rich halides Gd2IFe2, Gd2ICo2 and Gd2BrFe2

Abstract The critical behavior of the metal-rich halides Gd 2 IFe 2 , Gd 2 ICo 2 and Gd 2 BrFe 2 is investigated. These compounds crystallize in a layered structure exhibiting a sequence of Gd-(Fe,Co)-Gd layers enclosed between halogen atom layers. The critical exponents β, γ′, γ and δ obtained by several methods show a good agreement with the theorectical predictions derived for the 3d-XY model. This result implies a strong planar anisotropy caused by anisotropic exchange interactions induced by the 3d transition metal ions. In addition, the temperature dependence of the Kouvel-Fisher exponent γ ( T ) is discussed.