Complementary resonant X-ray and polarized neutron reflectometry study of chiral MnGe thin films

The temperature-field phase diagram of MnGe possesses topologically trivial one-dimensional helical or conical modulations with a wavelength that varies with temperature between 3 nm and 6 nm. There are also additional magnetic phases that are under dispute. Small-angle neutron scattering (SANS) data have been interpreted to show evidence of a topological magnetic phase consisting of localized three-dimensional spin textures called spin-hedgehogs [1]. Other studies claim that this phase is a multi-domain helical state [2,3]. The possibility of non-trivial textures in other regions of the phase diagram are not fully explored, including an unidentified magnetic phase in the bulk compound near the magnetic ordering temperature of T_C = 175 K [4].

Whereas pervious studies of MnGe films stabilize the metastable structure using either a MnSi or a FeGe template layer, we have grown epitaxial MnGe films on Si(111) substrates using a non-magnetic CrSi template layer. This allows us to study MnGe in the ultra-thin film limit without the influence of a neighboring magnetic layer. In this poster, we describe the use of a combination of resonant X-ray magnetic reflectometry (RXMR) and polarized neutron reflectometry (PNR) to investigate the depth-dependent magnetic structure of the helical state as well as well as the low-temperature phase that is currently under debate.

1. N. Kanazawa, et al. Phys. Rev. B 96, 220414 (2017).

2. J. Repicky, et al. , Science 374, 1484 (2021).

3. A. Yaouanc, et al., Phys. Rev. B 95, 174422 (2017)

4. R. Viennois, Europhysics Letters, 111 17008 (2015).