Exchange interactions of CaMnO3 in the bulk and at the surface

TL;DR

This study investigates the electronic and magnetic properties of CaMnO3, revealing how surface relaxation influences magnetic interactions and demonstrating the potential to induce spin flips through electron doping.

Contribution

The paper provides new insights into how structural relaxations affect exchange interactions and magnetic order at the surface of CaMnO3, supported by ab initio calculations.

Findings

Surface relaxation alters exchange interactions between Mn atoms.

Surface maintains G-type antiferromagnetic order after relaxation.

Electron doping can induce spin flip phenomena.

Abstract

In this work, we present electronic and magnetic properties of CaMnO3 (CMO) as obtained from ab initio calculations. We identify the preferable magnetic order by means of density functional theory plus Hubbard U calculations and extract the effective exchange parameters (Jij's) using the magnetic force theorem. We find that the effects of geometrical relaxation at the surface as well as the change of crystal field are very strong and are able to influence the lower energy magnetic configuration. In particular, our analysis reveals that the exchange interaction between the Mn atoms belonging to the surface and the subsurface layers is very sensitive to the structural changes. An earlier study [A. Filippetti and W.E. Pickett, Phys. Rev. Lett. 83, 4184 (1999)] suggested that this coupling is ferromagnetic and gives rise to the spin flip process on the surface of CMO. In our work we confirm their finding for an unrelaxed geometry, but once the structural relaxations are taken into account, this exchange coupling changes its sign. Thus, we suggest that the surface of CMO should have the same G-type antiferromagnetic order as in the bulk. Finally, we show that the suggested SF can be induced in the system by introducing an excess of electrons.