Density functional study of weak ferromagnetism in a thick BiCrO3 film

TL;DR

This study uses density functional theory to investigate the magnetic and structural properties of thick BiCrO3 films, revealing weak ferromagnetism induced by spin-orbit coupling and specific spin orientations.

Contribution

It provides the first detailed theoretical analysis of weak ferromagnetism in thick BiCrO3 films, including atomic structure and magnetic behavior.

Findings

BiCrO3 films maintain a tetragonal lattice up to 14,000 Å thickness.

The crystal is antiferroelectric with Pnma space group and noncollinear Bi displacements.

Weak ferromagnetism arises from spin-orbit coupling and can cancel depending on spin orientation.

Abstract

Very thick films of BiCrO$_3$ have been grown on a SrTiO$_3$ substrate, maintaining a tetragonal lattice up to thicknesses of 14,000\AA. Assuming we can treat films of this thickness as bulk crystals, we first calculated the experimentally undetermined atomic positions within the unit cell with the measured lattice constant of the film, then relaxed the lattice constants along with the atomic positions. All the calculations result in an antiferroelectric crystal with the {\it Pnma} space group with noncollinear Bi displacements. We find G-type antiferromagnetism with a spin-orbit induced weak ferromagnetic component, however, the weak ferromagnetic component can cancel if the antiferromagnetic spins are oriented along a particular one of the three 2-fold rotation axes.