Reentrant spin-glass behavior and enhanced Curie temperature in epitaxial MnSi*

We grew single crystal MnSi(111) thin films on Si(111) substrates by molecular beam epitaxy. The 3{\%} lattice mismatch created an in-plane tensile strain of $\varepsilon _{\vert \vert }$ = 0.005 $\pm $ 0.001, as measured by transmission electron microscopy, and induced an out-of-plane compressive strain $\varepsilon _{\bot }$= -0.0033 $\pm $ 0.0001, as determined by x-ray diffraction. The MnSi(111) films displayed two magnetic phases. The first transition from a paramagnetic phase to a phase with long range magnetic order occurs with an enhanced Curie temperature T$_{C}$ = 40 K as compared to bulk MnSi, which develops helical magnetic structure below T$_{C}$ = 29.5~K. This increase in T$_{C}$ can be explained by an in-plane strain. A second phase transition to spin glass, below T$_{f}$ = 35 K, maybe due to geometric frustration created by the compressive out-of-plain strain. We propose a relationship between the reentrant spin-glass behavior and the partial magnetic order reported for bulk MnSi under pressure.