Magnetic properties and critical behavior of disordered Fe_{1-x}Ru_x alloys: a Monte Carlo approach

摘要

We study the critical behavior of a quenched random-exchange Ising model withcompeting interactions on a bcc lattice. This model was introduced in the studyof the magnetic behavior of Fe_{1-x}Ru_x alloys for ruthenium concentrationsx=0%, x=4%, x=6%, and x=8%. Our study is carried out within a Monte Carloapproach, with the aid of a re-weighting multiple histogram technique. By meansof a finite-size scaling analysis of several thermodynamic quantities, takinginto account up to the leading irrelevant scaling field term, we find estimatesof the critical exponents \alpha, \beta, \gamma, and \nu, and of the criticaltemperatures of the model. Our results for x=0% are in excellent agreement withthose for the three-dimensional pure Ising model in the literature. We alsoshow that our critical exponent estimates for the disordered cases areconsistent with those reported for the transition line between paramagnetic andferromagnetic phases of both randomly dilute and $\pm J$ Ising models. Wecompare the behavior of the magnetization as a function of temperature withthat obtained by Paduani and Branco (2008), qualitatively confirming themean-field result. However, the comparison of the critical temperaturesobtained in this work with experimental measurements suggest that the model(initially obtained in a mean-field approach) needs to be modified.