Weakly spin-dependent band structures of antiferromagnetic perovskite LaMO$_3$ (M = Cr, Mn, Fe)

TL;DR

The paper investigates spin-dependent band structures in AFM LaCrO$_3$, LaMnO$_3$, and LaFeO$_3$ using spin-polarized DFT+$U$ across 15 structures. It introduces and validates a symmetry-based rule: if an exchange operation maps the up-spin potential to the down-spin potential and leaves a wave vector invariant, spin degeneracy occurs at that $\bm{k}$; otherwise, spin splitting relates energies at $\bm{k}$ and $\bm{k'}$ connected by the operation. Across all materials, the band structures are largely spin-degenerate with only small splittings on select lines, and the ground states are LaMnO$_3$ in A-AFM, LaCrO$_3$ and LaFeO$_3$ in G-AFM, in agreement with experiment. The near-degenerate spin behavior suggests symmetric spin-current contributions in doped electrodes, which could enhance OER/ORR performance but limits spin-current separation devices. The work thus provides a unified framework to understand spin-dependent electronic structure in AFM perovskites and highlights potential electrode-related implications.

Abstract

We investigate spin-dependent electronic states of antiferromagnetic (AFM) lanthanum chromite (LaCrO$_3$), lanthanum manganite (LaMnO$_3$), and lanthanum ferrite (LaFeO$_3$) using spin-polarized first-principles density functional theory (DFT) with Hubbard U correction. The band structures are calculated for 15 types of their different AFM structures. It is verified for these structures that there is a very simple rule to identify which wave number k exhibits spin splitting or degeneracy in the band structure. This rule uses the symmetry operations that map the up-spin atoms onto the down-spin atoms. The resulting spin splitting is very small for the most stable spin configuration of the most stable experimental structure. We discuss a plausible benefit of this characteristic, i.e., the direction-independence of the spin current, in electrode applications.

Figures (8)

• Figure 1: Oxygen octahedra surrounding Mn atom.
• Figure 2: Three types of distinct structures studied in this work; see also Supplementary Data (SD).
• Figure 3: Three different magnetic configurations, A-AFM, C-AFM, and G-AFM.
• Figure 4: (A) Unit cell and (B) Brillouin zone of the A-AFM LaMnO$_3$ experimental ORC structure. (C) Resulting band structure, in which red and blue lines denote up- and down-spin electron levels, respectively.
• Figure 5: (A) Unit cell and (B) Brillouin zone of the C-AFM LaMnO$_3$ experimental ORC structure. (C) Resulting band structure, in which red and blue lines denote up- and down-spin electron levels, respectively.