Experimental determination of exchange constants in antiferromagnetic Mn$_2$Au

TL;DR

This study experimentally measures the exchange constants in Mn$_2$Au, an antiferromagnetic material relevant for spintronics, using XMCD to distinguish between loose and AF coupled spins at different temperatures.

Contribution

It provides the first direct experimental determination of the AF exchange constant in Mn$_2$Au thin films using XMCD techniques.

Findings

AF exchange constant in Mn$_2$Au is (24 ± 5) meV.

XMCD effectively separates loose spin susceptibility from AF susceptibility.

Measurements at different temperatures help isolate intrinsic AF properties.

Abstract

Mn$_2$Au is an important antiferromagnetic (AF) material for spintronics applications. Due to its very high N\'eel temperature of about 1500 K, some of the basic properties are difficult to explore, such as the AF susceptibility and the exchange constants. Experimental determination of these properties is further complicated in thin films by unavoidable presence of uncompensated and quasiloose spins on antisites and at interfaces. Using x-ray magnetic circular dichroism (XMCD), we have measured the spin and orbital contribution to the susceptibility in the direction perpendicular to the in-plane magnetic moments of a Mn$_2$Au(001) film and in fields up to 8 T. By performing these measurements at a low temperature of 7 K and at room temperature, we were able to separate the loose spin contribution from the susceptibility of AF coupled spins. The value of the AF exchange constant obtained with this method for a 10 nm thick Mn$_2$Au(001) film equals to (24 $\pm$ 5) meV.