Quantum-confined charge transfer that enhances magnetic anisotropy in lanthanum M-type hexaferrites

TL;DR

This paper investigates how localized charge transfer in lanthanum hexaferrites enhances magnetic anisotropy, revealing electronic structure details that explain experimental observations and suggest potential for quantum transduction applications.

Contribution

It demonstrates that localized density functional theory reveals the origin of large magnetocrystalline anisotropy in lanthanum hexaferrites, highlighting charge transfer effects and electronic structure insights.

Findings

Localized charge transfer from lanthanum to iron produces a narrow 3d_{z^2} band.

Calculated anisotropy energies nearly double single-shot values and match experiments.

LaM's chemical similarity to other rare earths suggests potential for quantum transduction applications.

Abstract

Iron-based hexaferrites are critical-element-free permanent magnet components of magnetic devices. Of particular interest is electron-doped M-type hexaferrite i.e., LaFe$_{12}$O$_{19}$ (LaM) in which extra electrons introduced by lanthanum substitution of barium/strontium play a key role in uplifting the magnetocrystalline anisotropy. We investigate the electronic structure of lanthanum hexaferrite using a \textit{localized} density functional theory which reproduces semiconducting behavior and identifies the origin of the very large magnetocrystalline anisotropy. Localized charge transfer from lanthanum to the iron at the crystal's $2a$ site produces a narrow $3d_{z^2}$ valence band strongly locking the magnetization along the $c$ axis. The calculated uniaxial magnetic anisotropy energies from fully self-consistent calculations are nearly double the single-shot values, and agree well with available experiments. The chemical similarity of lanthanum to other rare earths suggests that LaM can host for other rare earths possessing non-trivial $4f$ electronic states for, \textit{e.g.,} microwave-optical quantum transduction.