Structure and magnetism of MnGe thin films grown with a nonmagnetic CrSi template

We report a method to grow B20 MnGe thin films using molecular-beam epitaxy, which employs an ultrathin CrSi template layer on Si(111). This layer is expected to be nonmagnetic, in contrast to MnSi and FeGe buffer layers that have been used previously. This template layer permits an investigation of the intrinsic properties of MnGe in the ultrathin-film limit without the influence of a neighboring magnetic layer. Single-phase MnGe(111) films were grown with thicknesses between 2 and $40\phantom{\rule{0.16em}{0ex}}\mathrm{n}\mathrm{m}$, which exhibited low interfacial roughnesses on the order of $0.6\phantom{\rule{0.16em}{0ex}}\mathrm{n}\mathrm{m}$. The films crystallized in a B20 structure with a small rhombohedral distortion. Magnetometry measurements in out-of-plane fields are consistent with a cone phase derived from helimagnetic order propagating along the film normal. However, an unexpected remanent moment develops below $35\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, concomitant with features in the field dependence of the transport data. This provides indirect evidence for the presence of a low-temperature phase which has been identified by others as either a triple-$Q$ topological spin-hedgehog lattice, or a multidomain single-$Q$ helical state.