Dzyaloshinskii-Moriya interaction chirality reversal with ferromagnetic thickness

TL;DR

This study demonstrates that the Dzyaloshinskii-Moriya interaction (DMI) chirality in ultrathin ferromagnetic films can be reversed solely by varying the ferromagnetic layer's thickness, supported by experimental and ab initio evidence.

Contribution

It reveals a new way to control DMI chirality through ferromagnetic thickness variations, supported by experimental data and theoretical calculations.

Findings

DMI chirality can be reversed by changing ferromagnetic thickness

Experimental results in Ta/FeCoB/TaOx support the thickness-dependent chirality reversal

Ab initio calculations explain the microscopic origin of the effect

Abstract

In ultrathin ferromagnetic films sandwiched between two distinct heavy metal layers or between a heavy metal and an oxide layer, the Dzyaloshinskii-Moriya interaction (DMI) is of interfacial origin. Its chirality and strength are determined by the properties of the adjacent heavy metals and the degree of oxidation at the interfaces. Here, we demonstrate that the DMI chirality can change solely with variations in the thickness of the ferromagnetic layer - an effect that has not been experimentally studied in details or explained until now. Our experimental observation in the trilayer system Ta/FeCoB/TaOx is supported by ab initio calculations: they reveal that variations in orbital filling and inter-atomic distances at the interface, driven by the structural relaxations in the ultrathin regime, lead to an inversion of DMI chirality. We hence propose a new degree of freedom to tune DMI chirality and the associated chiral spin textures by tailoring crystal structure e.g. using strain or surface acoustic waves.