Spin fluctuations, geometrical size effects, and zero-field topological order in textured MnSi thin films

Noncollinear magnetic structures with broken inversion symmetry have recently revolutionized the field of spintronics. Among them, transition metal monosilices and germanides are potential candidates due to their nontrivial spin textures. Here we report the growth and magnetic and electronic characterization of high-quality (111)-oriented thin films of MnSi by magnetron sputtering. While thicker films order magnetically similar to their bulk counterpart and according to previous reports in literature, x-ray magnetic circular dichroism measurements indicate that 30-nm-thick films do not develop long-range magnetic order, presumably due to magnetic frustration introduced by domains of different chiralities and spin disorder. X-ray absorption spectroscopy shows a stabilization of ${\mathrm{Mn}}⁺$ oxidation state in epitaxial thin films evidencing different electronic structure as compared with bulk MnSi. Field- and angular-dependent magnetoresistance support a magnetically disordered scenario, while Hall resistivity develops features of zero-field topological order formerly ascribed to skyrmions. Our results highlight the importance of geometrical size effects and spin disorder in noncentrosymmetric magnets and suggest that the topological Hall effect in thin films cannot be taken as the sole criterium for the assignment of nontrivial magnetic structures.