On Curie temperature of B20-MnSi films

TL;DR

This study investigates the Curie temperature of MnSi thin films, revealing an unexpected increase up to 43 K that appears linked to slight Mn excess and phonon softening, independent of structural variations.

Contribution

It demonstrates that MnSi films can have higher Curie temperatures due to stoichiometric deviations, regardless of structural differences.

Findings

Curie temperature reaches up to 43 K in thin films

Increased Curie temperature linked to Mn excess and phonon softening

Structural parameters have minimal impact on Curie temperature

Abstract

B20-type MnSi is the prototype magnetic skyrmion material. Thin films of MnSi show a higher Curie temperature than their bulk counterpart. However, it is not yet clear what mechanism leads to the increase of the Curie temperature. In this work, we grow MnSi films on Si(100) and Si(111) substrates with a broad variation in their structures. By controlling the Mn thickness and annealing parameters, the pure MnSi phase of polycrystalline and textured nature as well as the mixed phase of MnSi and MnSi1.7 are obtained. Surprisingly, all these MnSi films show an increased Curie temperature of up to around 43 K. The Curie temperature is likely independent of the structural parameters within our accessibility including the film thickness above a threshold, strain, cell volume and the mixture with MnSi1.7. However, a pronounced phonon softening is observed for all samples, which can tentatively be attributed to slight Mn excess from stoichiometry, leading to the increased Curie temperature.