Interplay between magnetisation dynamics and structure in MnCoGe thin films

Abstract We investigated the relation between magnetisation dynamics and microstructure in magnetocaloric MnCoGe thin films grown on two different substrates (Si or Ge). All the films show a hexagonal structure at room temperature, being polycrystalline when grown on Si substrates or displaying highly textured columnar grains with same orientation when grown on Ge substrates. Their static and dynamic magnetic properties present anomalies at lower temperature, with pronounced or singular features observed only for the highly textured samples : a significant modification of the magnetisation dynamics, as a large decoherence of the uniform resonance mode measured by ferromagnetic resonance (FMR) is found between 200 K and 10 K, when the magnetic field is applied normal to the surface, pointing to a spin order transition or a distorted structure with a canted spin arrangement. Below a freezing temperature, typical features of spin-glass like non-equilibrium dynamics are noted in the magnetic relaxation and memory effects suggesting magnetic frustration and disorder. In addition, the in-plane angular dependence of the resonance field displays a partial transition from the hexagonal phase below 200 K that can be attributed to the distortion of the hexagonal lattice with a canted spin arrangement observed in doped samples. The FMR linewidth increases strongly in this temperature range indicating a high magnetic damping, which is equally observed for the samples grown on Si below 40 K.