MAGNETIC PHASE TRANSITION IN THE METAL-RICH RARE-EARTH CARBIDE HALIDES GD(2)XC (X=BR,I)

摘要

The critical behavior of the ferromagnetic-paramagnetic phase transition of metal-rich rare-earth carbide halides Gd2BrC and Gd2IC is investigated. These compounds exhibit a layered structure of Gd-C-Gd slabs which are sandwiched between layers of halogen atoms (Br,I). The critical exponents beta, gamma', gamma, and delta are determined by several methods: modified Arrott plots, Kouvel-Fisher plots, scaling plots, and ln J vs ln(mu(0)H) plots. The asymptotic critical exponents beta and gamma as well as the critical amplitudes J(0) and h(0)/J(0) were determined from both the Kouvel-Fisher and the correction to scaling analysis. The derived critical exponents are identical for all methods and in good agreement with the predictions of the three-dimensional Heisenberg model whereas the reduced critical amplitudes J(0)/J(s)(0), mu h(0)/k(B) T-c, and D J(0)(delta)/h(0) cannot be related to a particular model. The temperature dependence of the Kouvel-Fisher exponent gamma(T) is discussed with respect to chemical disorder. [References: 52]