First-principles study of structurally modulated multiferroic CaMn$_7$O$_{12}$

TL;DR

This study uses first-principles calculations to analyze the electronic and magnetic structures of multiferroic CaMn$_7$O$_{12}$, revealing orbital modulation, magnetic coupling, and polarization mechanisms based on experimental crystal data.

Contribution

It provides a detailed first-principles analysis of the multiferroic CaMn$_7$O$_{12}$, highlighting the orbital modulation and the mechanisms contributing to its polarization.

Findings

Mn2 sites exhibit 3d orbital modulation due to Jahn-Teller distortions.

Magnetic structure of Mn3 sites is anharmonically modulated via orbital coupling.

Both Dzyaloshinskii-Moriya and exchange striction mechanisms contribute to polarization.

Abstract

We study the electronic and magnetic structures of multiferroic CaMn$_7$O$_{12}$ by first-principle calculations, based on the experimentally determined modulated crystal structure. We confirm the presence of a 3$d$ orbital modulation of the Mn2 (Mn$^{3+}$) sites, previously inferred from the Jahn-Teller crystal distortions. Our results indicate that in the multiferroic phase the magnetic structure of the Mn3 (Mn$^{4+}$) sites is anharmonically modulated via orbitally-mediated coupling with the structural modulation, and that the Dzyaloshinskii-Moriya and exchange striction mechanisms contribute equally to the polarization