CANADA: Polarised neutron reflectometry of the helical magnetism in thin film MnGe

MnGe is a chiral magnetic material that potentially possesses multiple interesting topological states. Although the cubic B20 phase is not thermodynamically stable in bulk, we have used molecular beam epitaxy to synthesise the first magnetically isolated MnGe films using paramagnetic CrSi as a template layer, in place of the magnetic seed layers used by others. Preliminary polarised neutron reflectometry (PNR) performed at POLREF was complicated by the low contrast in the scattering length density between MnGe and the Si substrate. We propose to continue our investigation of the controversial phase diagram of MnGe thin films by producing new samples better suited for PNR. By increasing the thickness of the template layer, we show that the expected reflectivity is drastically increased. We will use PNR to probe a controversial low-temperature phase, and characterise the temperature dependence of the helical pitch. We will investigate how finite size effects affect the competition between discrete helicoids and other magnetic textures, and potentially find evidence for a novel chiral interaction predicted to exist in MnGe.