Sm substitution effect on the critical behaviour of Laves phase Gd1−xSmxCo2 intermetallic nearby the ferromagnetic-paramagnetic phase transition

Abstract

In this work, we present a comparative and detailed study of the critical behavior near ferromagnetic-paramagnetic phase transition in the intermetallic Laves phase compounds Gd1−xSmxCo2, x = 0.5, 0.6 and 0.7. The investigated samples exhibit a second-order phase transition at Curie temperature TC. The critical exponents β, γ, and δ have been estimated through diverse techniques: the Modified Arrott plot, the Kouvel-Fisher plot, the critical isotherm technique, and the magnetocaloric effect method. The critical exponents values that were determined have been validated using the universal scaling hypothesis, wherein the isotherm magnetization curves M(H) converge into two distinct universal branches below and above TC. The substitution of Gd by Sm changes the universality class in the (Gd,Sm)Co2 compounds. For the sample Gd0.5Sm0.5Co2, the critical exponents obtained are closely consistent with the predictions of the 3D-Heisenberg model featuring a magnetic system with a short-range exchange interaction. While, for both samples Gd0.4Sm0.6Co2 and Gd0.3Sm0.7Co2, the values deviate from known theoretical models and might belong to an unconventional universality class with an intermediate-range exchange interaction.