3d-XY critical behavior of the layered metal-rich halides Gd2IFe2, Gd2ICo2 and Gd2BrFe2

Abstract The magnetic phase transition of the metal-rich halides Gd 2 IFe 2 , Gd 2 ICo 2 and Gd 2 BrFe 2 is investigated by magnetization measurements. 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 are determined together with the reduced critical amplitudes J 0 / J S (0), μh 0 / k B T C and DJ 0 δ h / 0 . For the determination of the critical exponents we use several methods: modified Arrot plots, method of Kouvel-Fisher, scaling plots and In J versus ln( μ 0 H ) plots. The results are compared with theoretical predictions for homogeneous ferromagnets. In addition, the temperature dependence of the Kouvel-Fisher exponent γ ( T ) is discussed.