Magneto-optische und magnetische Untersuchungen an MBE gewachsenen MnS- und MnCrS-Strukturen

With regard to the constant miniaturization of established electronic devices the point will be reached where the intrinsic properties of these materials differ from the fundamental characteristics of the corresponding bulk structures. Particularly for ferro- and antiferro-magnetic materials these properties are still not fully understood. Hence, with the help of molecular beam epitaxy grown zinc blende ZnSe/MnS/ZnSe structures on a GaAs-Substrate the open question on the properties of these low dimensional Materials will be answered. Therefore the influence of a reduced dimension by a successive decrease of the layer thickness of the antiferromagnetic MnS films as well as the effect of an incorporation of chromium into the MnS is studied. By a time resolved, temperature and magnetic field dependent investigation of a characteristic emission of the Manganese 3d electrons which are responsible for the magnetism, a detailed analysis of the magnetic properties of MnS down to real two dimensional structures becomes possible. One result of these experiments is that the thinnest MnS layer (1.8nm) shows a phase diagram of a two dimensional Heisenberg-spin-system with a weak uniaxial anisotropy along the growth direction of the layer structure. Additionally, common techniques like SQUID measurements and electron spin resonance spectroscopy confirm these results. However, these Methods reach their resolution limit. The measurement concepts developed for MnS were transferred on MnCrS layer structures with increasing chromium content. These studies show a significant increase of the magnetic phase transition as well as a change from an antiferro- to a more ferromagnetic character of the MnCrS system with the incorporation of chromium.