Magnetic properties and critical behavior of disordered Fe1−xRuxalloys: A Monte Carlo approach

Abstract

We study the critical behavior of a quenched random-exchange Ising model with competing interactions on a bcc lattice. This model was introduced in the study of the magnetic behavior of Fe 1−x Ru x alloys for ruthenium concentrations x = 0%, x = 4%, x = 6%, and x = 8%. Our study is carried out within a Monte Carlo approach, with the aid of a re-weighting multiple histogram technique. By means of a finite-size scaling analysis of several thermodynamic quantities, taking into account up to the leading irrelevant scaling field term, we find estimates of the critical exponents α, β, γ, and ν, and of the critical temperatures of the model. Our results for x = 0% are in excellent agreement with those for the three-dimensional pure Ising model in the literature.We also show that our critical exponent estimates for the disordered cases are consistent with those reported for the transition line between paramagnetic and ferromagnetic phases of both randomly dilute and ±J Ising models. We compare the behavior of the magnetization as a function of temperature with that obtained by Paduani and Branco (2008), qualitatively confirming the mean-field result. However, the comparison of the critical temperatures obtained in this work with experimental measurements suggest that the model (initially obtained in a mean-field approach) needs to be modified.

Cluster size effects in the magnetic properties of Fe$_p$-Al$_{q=1-p}$ alloys

“…From there we obtain T c = 6.3542(2). This critical temperature for q = 0 agrees very well with the previous one obtained from the susceptibility, and also with the high-temperature series expansion estimate by Butera and Comi T c = 6.35435(3) [40] and with other Monte Carlo results T c = 6.35441(5) [43], and T c = 6.3544(6) [25]. This is a quite nice numerical way for us to test the implementations that have been done in the computer codes.…”

“…Such cluster size properties have not been considered previously and better fits than those from Refs. [15][16][17][18][19][20][21][22][23][24][25][26][27] have been achieved. In addition, Monte Carlo simulations provide not only more precise values for the transition temperatures, but also can capture the real physics of the cluster size properties.…”

“…In order to try to explain this rather anomalous behavior of the phase diagram, several models (including classical and quantum) and theoretical procedures (including analytical approximations and computer simulations), have been proposed in the literature (without any intention of making an extensive review of the previous studies in these alloys, we can cite, for instance, references [15][16][17][18][19][20][21][22][23][24][25][26][27]). It should be mentioned that, despite localized spin Hamiltonians are not completely appropriate for the study of these metallic alloys, there are some experimental evidences and first principles calculations making possible the choice of localized models instead of the itinerant ones, as discussed, respectively, in Refs.…”