Phase diagram description of the CaCu$_3$Fe$_4$O$_{12}$ double perovskite

Ivon R. Buitrago; C. I. Ventura; R. Allub

doi:10.1063/1.5032206

paper

Phase diagram description of the CaCu $_{3}$ Fe $_{4}$ O $_{12}$ double perovskite

arXiv:1804.05726 · doi:10.1063/1.5032206

Abstract

CaCu $_{3}$ Fe $_{4}$ O $_{12}$ exhibits a temperature-induced transition from a ferrimagnetic-insulating phase, in which Fe appears charge disproportionated, as Fe $^{3 +}$ and Fe $^{5 +}$ , to a paramagnetic-metallic phase at temperatures above 210 K, with Fe $^{4 +}$ present. To describe it, we propose a microscopic effective model with two interpenetrating sublattices of Fe $^{(4 - δ) +}$ and Fe $^{(4 + δ) +}$ , respectively, being $δ$ the Fe-charge disproportionation. We include all $3 d$ -Fe orbitals: $t_{2 g}$ localized orbitals, with spin 3/2 and magnetically coupled, plus two degenerate itinerant $e_{g}$ orbitals with local and nearest-neighbor (NN) electron correlations, and hopping between NN $e_{g}$ orbitals of the same symmetry. Allub and Alascio previously proposed a model to describe the phase transition in LaCu $_{3}$ Fe $_{4}$ O $_{12}$ from a paramagnetic-metal to an antiferromagnetic-insulator, induced by temperature or pressure, involving charge transfer between Fe and Cu ions, in contrast to Fe-charge disproportionation. With the model proposed for CaCu $_{3}$ Fe $_{4}$ O $_{12}$ , modified to account for this difference between the two compounds, the density of states of the itinerant Fe orbitals was obtained, using Green's functions methods. The phase diagram for CaCu $_{3}$ Fe $_{4}$ O $_{12}$ was calculated, including phases exhibiting Fe-charge disproportionation, where the two eg orbitals in each site are symmetrically occupied, as well as novel phases exhibiting local orbital selectivity/asymmetric occupation of $e_{g}$ orbitals. Both kinds of phases may exhibit paramagnetism and ferromagnetism. We determined the model parameters which best describe the phase transition observed in CaCu $_{3}$ Fe $_{4}$ O $_{12}$ , and found other phases at different parameter ranges, which might be relevant for other compounds of the ACu $_{3}$ Fe $_{4}$ O $_{12}$ family, which present both types of transitions.

11 pages, 12 figures

Phase diagram description of the CaCu3​Fe4​O12​ double perovskite

Abstract

Phase diagram description of the CaCu $_{3}$ Fe $_{4}$ O $_{12}$ double perovskite