Structure-property relationship of Co$_2$MnSi thin films in response to He$^+$ -irradiation

TL;DR

This study examines how He$^+$ ion irradiation affects the crystal structure and magnetic properties of Co$_2$MnSi thin films, revealing a transition from ordered to disordered phases and corresponding magnetic degradation.

Contribution

It provides a detailed analysis of the structural and magnetic evolution of Co$_2$MnSi films under ion irradiation using NMR and TEM, highlighting the disorder transition process.

Findings

Transition from $L2_1$ to $A2$ structure with increasing fluence

Decreased magnetic saturation moment correlates with structural disorder

Disorder initiates at the upper part of the films

Abstract

We investigated the structure-property relationship of Co$_2$MnSi Heusler thin films upon the irradiation with He$^+$ ions. The variation of the crystal structure with increasing ion fluence has been probed using nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM), and associated with the corresponding changes of the magnetic behavior. A decrease of both the structural order and the moment in saturation is observed. Specifically, we detect a direct transition from a highly $L2_1$-ordered to a fully $A2$-disordered structure type and quantify the evolution of the $A2$ structural contribution as a function of ion fluence. Complementary TEM analysis reveals a spatially-resolved distribution of the $L2_1$ and $A2$ phases showing that the $A2$ disorder starts at the upper part of the films. The structural degradation in turn leads to a decreasing magnetic moment in saturation in response to the increasing fluence.