First-principles stabilization of an unconventional collinear magnetic ordering in distorted manganites

TL;DR

This study uses first-principles calculations to identify the AFM-E magnetic ordering as the ground state in distorted orthorhombic manganites, highlighting the importance of structural distortions over chemical effects.

Contribution

It demonstrates that the AFM-E magnetic order is stabilized by octahedral distortions and provides detailed exchange constants, advancing understanding of magnetic phases in manganites.

Findings

AFM-E is the magnetic ground state in HoMnO3.

Structural distortions are more influential than chemical effects.

The phase is insulating with a 0.5 eV band gap.

Abstract

First-principles calculations have been performed for different collinear magnetic orderings in orthorhombic manganites, such as HoMnO3, TbMnO3 and YMnO3, showing large GdFeO3-like distortions. Our results suggest that the AFM-E type ordering, experimentally observed in HoMnO3 and recently proposed from model hamiltonian studies as a potentially novel phase, is indeed the magnetic ground state. Its stability is strongly connected with octahedral distortions and points to the relevance of structural more than chemical effects. The calculated exchange constants, extracted from a Heisenberg model used to fit the first-principles total energies, show that the ferromagnetic in-plane nearest-neighbour coupling is reduced compared to less-distorted manganites, such as LaMnO3. In parallel, the antiferromagnetic next-nearest-neighbour coupling along planar Mn-O-O-Mn paths in highly-distorted manganites plays a relevant role in the stabilization of the AFM-E spin configuration. In agreement with experiments, the density of states shows that this phase is insulating with an indirect band-gap of about 0.5 eV.