Research: Structure-property relationship of Co2MnSi thin films in response to He+-irradiation

Chemical order has a strong impact on the properties of any given material. Hence, understanding and controlling the structure-property relationship is a crucial factor for their use in high-end applications. One route to tune the structure of functional materials is the irradiation with light ions, which is known to strongly modify their magnetic properties. In order to get insight into the structure-property relationship of the potential half-metallic ferromagnet Co₂MnSi, we applied a combination of magnetometry, nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) on Co₂MnSi thin films exposed to He+-irradiation. While NMR probes the local environment of the investigated nuclei over the entire sample volume, TEM provides structural information of selected regions of the sample. The evolution of the (local) structure as function of ion fluence is in turn linked to the macroscopic magnetic properties. Specifically, by means of NMR we observe a quantitative evolution from L2₁ to A2 type structure as function of ion fluence. Complementary HRTEM analysis reveals that the A2 disorder starts at the upper part of the films. This degradation of structure in turn leads to a decreasing magnetic moment in saturation in response to increasing fluence. Our results underline that structure analysis by NMR, which allows quantitative determination of phase fractions on an integral scale, and by TEM, which enables imaging down to the atomic scale, complement each other very well. 

F. Hammerath, R. Bali, R. Hübner, M. R. D. Brandt, S. Rodan, K. Potzger, R. Böttger, Y. Sakuraba, S. Wurmehl,
Structure-property relationship of Co₂MnSi thin films in response to He⁺-irradiation,
Sci. Rep. 9, 2766 (2019)