Theoretical study of the intrinsic magnetic properties of disordered Fe_1−xRu_xalloys: a mean-field approach

Abstract

The magnetic properties of the Fe 1−x Ru x alloy system for 0 x 0.10 are studied by using a mean-field approximation based on the Bogoliubov inequality. Ferromagnetic Fe-Fe spin correlations and antiferromagnetic Fe-Ru and Ru-Ru exchanges have been considered for describing the temperature dependence of the Curie temperature and low temperature magnetization. A composition dependence has been imposed in the exchange couplings, as indicated by experiments. From a procedure of least-square fitting to the experimental results an estimation of the interaction parameters was obtained, which yielded the low temperature dependence of the magnetization and that of the ferromagnetic Curie temperature. Good agreement was obtained with available experimental results.

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

“…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.We study the magnetic properties and critical behavior of a quenched random-exchange Ising model, through extensive Monte Carlo simulations.…”

“…Combining the estimates obtained in those fits, presented in Tab. IV, we obtain:T c = 6.3544(6), or K c = 0.15737(1), which is in excellent agreement with K HTS c = 0.1573725(6)[20] and with another Monte Carlo…”

“…x ≈ 30%, the system undergoes a crystallographic transition to an hcp structure. While in the bcc structure, the lattice parameter increases steadily with the Ruthenium concentration (2) 10% 838 (2) The model proposed by Paduani and Branco (2008) consists of Fe and Ru atoms randomly distributed on a bcc lattice with probabilities 1 − x and x respectively. Each atom has a magnetic degree of freedom that is assumed to behave as an Ising-like spin, so the system is described by a spin-1/2 Ising Hamiltonian…”

“…Pure evaluation [26], K c = 0.157371 (1). We can use ourT c to estimate the exchange integral of the Fe-Fe bond, J FeFe ≡ J, just by combining the experimental T c in Tab.…”

“…Our starting point was the model proposed in Ref. 1, consisting of iron and ruthenium atoms randomly distributed in a bodycentered cubic (bcc) lattice, with probabilities 1−x and x, respectively. In this model, atoms are treated as Ising spins, Fe-Fe bonds are ferromagnetic (FM), with exchange integral J, while Fe-Ru and Ru-Ru interactions are antiferromagnetic (AF) with exchange integrals −λJ and −ξJ, respectively, where λ and ξ depend on the ruthenium concentration, x, as follows: λ ≡ ξ = ξ 0 − ξ 1 x.…”