Enhanced critical fields in MnSi thin films

Abstract

The magnetic properties of the cubic helimagnet MnSi are governed by the Dzyaloshinskii-Moriya interaction which in the bulk stabilizes a helical ground state below 29 K with a spin-helix wavelength of 18 nm and a propagation vector along the [111] direction. Recently, MnSi has attracted a lot of attention after a skyrmion lattice had been discovered in the so called A-phase. We have prepared thin MnSi films on Si(111) substrates by codeposition of Mn and Si. Two films with a thickness below and above the spin helix length have been investigated using SQUID magnetometry. In comparison to bulk material, the films show an enhanced magnetic ordering temperature of 45 K. Magnetoresistance measurements performed on the films reveal a decrease of the resistivity with increasing field. They show together with the magnetic characterization that the critical fields describing the transition from the helical to a conical spin phase and from the conical phase to a parallel spin alignment are dependent on the film thickness and enhanced in comparison to single crystalline MnSi. The form anisotropy which prefers a spin alignment in the film plane is suggested to be the origin for the enhancement of the critical fields.