Exchange interaction in ACu3Fe2Re2O12 quadruple perovskites

TL;DR

This work addresses the origin and tuning of high Curie temperatures in the quadruple perovskites ACu$_3$Fe$_2$Re$_2$O$_{12}$ by performing DFT+$U$ calculations to determine electronic structure and exchange constants, and by estimating $T_C$ with mean-field and Onsager reaction field theory. The authors find a robust half-metallic ferrimagnetic ground state governed by strong AFM Cu–Re and Fe–Re exchanges, with Re$^{5d}$ states contributing itinerant magnetism that scales with Re $t_{2g}$ occupancy. The proposed band-magnetism mechanism explains why $T_C$ increases with Re occupancy and why Os substitution yields sizeable Cu–Os exchange, while ORF corrections bring theoretical $T_C$ into close agreement with experiment for most compositions. The results offer a coherent framework linking electronic structure, exchange pathways, and finite-temperature magnetism in these complex oxides, with implications for designing high-$T_C$ spintronic materials by targeted tuning of Re occupancy and chemical composition.

Abstract

Quadruple perovskites ACu$_3$Fe$_2$Re$_2$O$_{12}$ attract considerable interest due to their high Curie temperatures (up to $710$K), which strongly depend on the A-site cation. In this work, we employ first-principles calculations to investigate their electronic structure and magnetic exchange interactions. A band mechanism of magnetism that explains the antiferromagnetic character of the exchange interactions and their strong dependence on the filling of the Re $t_{2g}$ states is proposed. These antiferromagnetic interactions stabilize ferrimagnetic ground state. The calculated Curie temperatures, obtained within the Onsager reaction field theory, are in a good agreement with experimental data.

Figures (7)

• Figure 1: The crystal structure of ACu$_3$Fe$_2$Re$_2$O$_{12}$ quadruple perovskites.
• Figure 2: Band structures comparison of NaCu$_3$Fe$_2$Re$_2$O$_{12}$ obtained by DFT+U calculation. Initial DFT+U bands are shown in black, projected on Wannier functions are in red. The left panel illustrates the majority-spin channel, and the right panel -- the minority-spin channel.
• Figure 3: Wannier orbitals (Cu $x^2-y^2$ and Re $xy$) employed for the calculation of the exchange parameter $J_{\rm Cu-Re}$.
• Figure 4: Density of states (DOS) as obtained in DFT+U calculations. Due to different valences of A ions Re is expected to have $n_{{\rm Re-d}}^{{\rm nominal}}=1.5$ for Ag or $n_{{\rm Re-d}}^{{\rm nominal}}=2.5$ electrons on $t_{2g}$ shell for Dy. Positive (negative) DOS correspond to spin majority (minority).
• Figure 5: Density of states (DOS) as obtained in DFT+U (symbols for partial DOS and shaded background for total DOS) and DFT+U+SOC (solid lines) calculations for LaCu$_3$Fe$_2$Re$_2$O$_{12}$.