Spin-spiral state of a Mn monolayer on W(110) studied by soft x-ray absorption spectroscopy at variable temperatures

TL;DR

This study uses soft x-ray absorption spectroscopy and ab initio calculations to identify the antiferromagnetic cycloidal spin spiral as the ground state of a Mn monolayer on W(110), revealing temperature-dependent magnetic properties without a phase transition.

Contribution

It demonstrates how XLD signals can distinguish between helical and cycloidal spirals, confirming the cycloidal spiral as the magnetic ground state of Mn/W(110).

Findings

Mn monolayer on W(110) has an AFM cycloidal spin spiral ground state.

XLD signals differentiate between helical and cycloidal spirals.

Magnetic properties vary with temperature but show no phase transition up to 300 K.

Abstract

The noncollinear magnetic state of epitaxial Mn monolayers on tungsten (110) crystal surfaces is investigated by means of soft x-ray absorption spectroscopy, to complement earlier spin-polarized STM experiments. X-ray absorption spectra (XAS), x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) Mn L23-edge spectra were measured in the temperature range from 8 to 300 K and compared to results of fully-relativistic ab initio calculations. We show that antiferromagnetic (AFM) helical and cycloidal spirals give rise to significantly different Mn L23-edge XLD signals, enabling thus to distinguish between them. It follows from our results that the magnetic ground state of a Mn monolayer on W(110) is an AFM cycloidal spin spiral. Based on temperature-dependent XAS, XLD and field-induced XMCD spectra we deduce that magnetic properties of the Mn monolayer on W(110) vary with temperature, but this variation lacks a clear indication of a phase transition in the investigated temperature range up to 300 K - even though a crossover exists around 170 K in the temperature dependence of XAS branching ratios and in XLD profiles.