Magnetic phase transition in the metal-rich rare-earth carbide halides Gd2XC (X= Br,I).

Abstract

The critical behavior of the ferromagnetic-paramagnetic phase transition of metal-rich rare-earth carbide halides ${\mathrm{Gd}}_{2}$BrC and ${\mathrm{Gd}}_{2}$IC 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 \ensuremath{\beta}, \ensuremath{\gamma}', \ensuremath{\gamma}, and \ensuremath{\delta} are determined by several methods: modified Arrott plots, Kouvel-Fisher plots, scaling plots, and lnJ vs ln(${\mathrm{\ensuremath{\mu}}}_{0}$H) plots. The asymptotic critical exponents \ensuremath{\beta} and \ensuremath{\gamma} as well as the critical amplitudes ${\mathit{J}}_{0}$ and ${\mathit{h}}_{0}$/${\mathit{J}}_{0}$ 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 ${\mathit{J}}_{0}$/${\mathit{J}}_{\mathit{S}}$(0), \ensuremath{\mu} ${\mathit{h}}_{0}$/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$, and ${\mathit{DJ}}_{0}^{\mathrm{\ensuremath{\delta}}}$/${\mathit{h}}_{0}$ cannot be related to a particular model. The temperature dependence of the Kouvel-Fisher exponent \ensuremath{\gamma}(T) is discussed with respect to chemical disorder.