Identifying the octupole Antiferromagnetic domain orientation in Mn$_{3}$NiN by scanning Anomalous Nernst Effect microscopy

TL;DR

This study uses scanning anomalous Nernst effect microscopy to image and identify octupole antiferromagnetic domains in Mn$_{3}$NiN thin films, revealing domain structures and their response to temperature and magnetic fields.

Contribution

It introduces a novel imaging technique combining the anomalous Nernst effect with laser scanning to visualize antiferromagnetic domain arrangements in Mn$_{3}$NiN.

Findings

Identification of octupole antiferromagnetic domains

Checkerboard domain pattern observed after cooling in magnetic field

Estimated macrodomain size of approximately 1 μm²

Abstract

The intrinsic anomalous Nernst effect in a magnetic material is governed by the Berry curvature at the Fermi energy and can be realized in non-collinear antiferromagnets with vanishing magnetization. Thin films of (001)-oriented Mn$_{3}$NiN have their chiral antiferromagnetic structure located in the (111) plane facilitating the anomalous Nernst effect unusually in two orthogonal in-plane directions. The sign of each component of the anomalous Nernst effect is determined by the local antiferromagnetic domain state. In this work, a temperature gradient is induced in a 50 nm thick Mn$_{3}$NiN two micron-size Hall cross by a focused scanning laser beam, and the spatial distribution of the anomalous Nernst voltage is used to image and identify the octupole macrodomain arrangement. Although the focused laser beam width may span many individual domains, cooling from room temperature through the antiferromagnetic transition temperature in an in-plane magnetic field prepares the domain state producing a checkerboard pattern resulting from the convolution of contributions from each domain. These images together with atomistic and micromagnetic simulations suggest an average macrodomain of the order of $1 {\mu}m^{2}$.