Investigation of Altermagnetic Candidate Mn5Si3 and MnSi-Mn5Si3 Mixed Phases

Altermagnets have attracted significant attention for combining antiferromagnetic features such as vanishing net magnetization and ultrafast spin dynamics with properties typically associated with ferromagnets, making them promising for spintronic applications. One candidate material for this emerging magnetic category is Mn5Si3. In this study, we propose using polarized neutron reflectometry on the POLREF instrument to investigate the magnetic structure of three thin film samples: pure Mn5Si3, MnSi and a mixed MnSix. These samples provide a platform to explore the emergence of altermagnetic order in Mn5Si3 and its possible interaction with the known helimagnet, MnSi. Magnetotransport measurements show an unexpected negative and isotropic magnetoresistance. Polarized neutron reflectometry will be used to determine the structural quality and phase uniformity of the Mn₅Si₃ and MnSi films, and to assess whether the mixed phase MnSix forms distinct layers or uniformly distributed phase-separated clusters. The strong contrast in neutron scattering length density between Mn5Si3 and MnSi makes polarized neutron reflectometry especially effective for this system, where X-ray scattering lacks sufficient contrast. These measurements will enable depth-resolved profiles of the magnetic moment within each phase as well as allow us to better determine the distributions and changes in magnetization when both phases are present.