Out-of-plane nesting driven spin spiral in ultrathin Fe/Cu(001) films

TL;DR

This study reveals that out-of-plane Fermi surface nesting drives the formation of a spin spiral in ultrathin Fe/Cu(001) films, highlighting the significance of three-dimensional electronic structure in magnetic ordering.

Contribution

It demonstrates the out-of-plane Fermi surface nesting as the origin of spin spirals in ultrathin Fe films, using advanced photoemission spectroscopy and reciprocal space analysis.

Findings

Out-of-plane Fermi surfaces are drastically modified compared to in-plane surfaces.

A real space compressive strain of 1.5% along the c-axis was measured.

The incommensurate ordering vector q is approximately (0,0,0.86) in reciprocal units.

Abstract

Epitaxial ultrathin Fe films on fcc Cu(001) exhibit a spin spiral (SS), in contrast to the ferromagnetism of bulk bcc Fe. We study the in-plane and out-of-plane Fermi surfaces (FSs) of the SS in 8 monolayer Fe/Cu(001) films using energy dependent soft x-ray momentum-resolved photoemission spectroscopy. We show that the SS originates in nested regions confined to out-of-plane FSs, which are drastically modified compared to in-plane FSs. From precise reciprocal space maps in successive zones, we obtain the associated real space compressive strain of 1.5+-0.5% along c-axis. An autocorrelation analysis quantifies the incommensurate ordering vector q=(2pi/a)(0,0,~0.86), favoring a SS and consistent with magneto-optic Kerr effect experiments. The results reveal the importance of in-plane and out-of-plane FS mapping for ultrathin films.