Competition of Dzyaloshinskii-Moriya and higher-order exchange interactions in Rh/Fe atomic bilayers on Ir(111)

TL;DR

This study uncovers how stacking sequence influences complex noncollinear spin structures in Rh/Fe bilayers on Ir(111), revealing the competition between Dzyaloshinskii-Moriya and higher-order exchange interactions.

Contribution

It demonstrates the impact of stacking sequence on higher-order exchange interactions and the resulting novel spin configurations in Rh/Fe bilayers on Ir(111).

Findings

Frustrated exchange interactions lead to a spin spiral in fcc stacking.

hcp stacking favors a double-row antiferromagnetic state.

Dzyaloshinskii-Moriya interaction causes a small canting angle.

Abstract

Using spin-polarized scanning tunneling microscopy and density functional theory we demonstrate the occurrence of a novel type of noncollinear spin structure in Rh/Fe atomic bilayers on Ir(111). We find that higher-order exchange interactions depend sensitively on the stacking sequence. For fcc-Rh/Fe/Ir(111) frustrated exchange interactions are dominant and lead to the formation of a spin spiral ground state with a period of about 1.5 nm. For hcp-Rh/Fe/Ir(111) higher-order exchange interactions favor a double-row wise antiferromagnetic or "uudd" state. However, the Dzyaloshinskii- Moriya interaction at the Fe/Ir interface leads to a small angle of about 4{\deg} between adjacent magnetic moments resulting in a canted "uudd" ground state.