Nuclear magnetic resonance reveals structural evolution upon annealing in epitaxial Co2MnSi Heusler films.

Co2MnSi films were recently reported to show a significant increase in current-perpendicular-to-plane-giant-magnetoresistance upon annealing. Here, nuclear magnetic resonance was used to study the impact of annealing on the structure of such films. Below 550 °C, no long-range L21-order is observed, while annealing above 550 °C leads to the formation of the ideal L21 configuration, however, with a distinct degree of off-stoichiometry. Further evidence from restoring field measurements hints that interdiffusion may account for the drop in magnetoresistance observed for samples annealed above 600 °C. These results show that optimizing films for spintronics involves the identification of the best annealing temperature, high enough for long-range order to emerge, but low enough to maintain smooth interfaces. [ABSTRACT FROM AUTHOR]