Non-collinear magnets form the basis of several new concepts in fundamental and applied science. They can host chiral topologically protected states like skyrmion phases which are an exciting object of condensed matter research. Moreover, such systems can be stabilized at ambient temperature and are promising materials for applications in next-generation memory devices based on spin manipulation (spintronics).
Tetragonal Heusler phases based on Mn3Ge, Mn2RhSn and Mn2PtSn recently were found to be versatile hosts for non-collinear spin structures. Here, the formation of non-collinear spin structures is a consequence of competing interactions and may occur for instance in acentric crystal structures when ferromagnetic exchange interactions compete with the spin-orbit- interaction induced Dzaloshinskii-Moriya interaction. A typical example are spiral spin structures, which by varying external parameters as temperature, pressure or magnetic field may be transformed into skyrmions.. The recent discovery of a new type of spin texture, so-called antiskyrmions, in the tetragonal Heusler phase Mn1.4Pt0.9Pd0.1Sn, which even persists above room temperature, nicely illustrates the potential of this class of compounds for applications in this field.
In this project we want to explore systematically the conditions for the formation of non-collinear spin structures, in particular those favouring the formation of skyrmions, in tetragonal Mn-based Heusler systems. For this purpose the above mentioned Heusler systems will be chemically modified. Bulk as well as thin film samples will be synthesized and their magnetic properties will be studied by using magnetization and magnetotransport measurements as well as by local probe techniques like nuclear magnetic resonance, muon spin resonance and Mössbauer spectroscopy. The supervisors of this project are experts in the application of these methods on quantum magnets and unconventional superconductors. The experimental work will perfomed at the MPI-CPfS and the TU Dresden as well as at international high intensity proton accelerator facilities such as the Paul-Scherrer-Institute near zürich. Switzerland. Direct imaging of skyrmion phases will be performed in collaboration with the research group of Professor S.S.P. Parkin by Lorentz transmission electron microscopy (LTEM) at Max Planck Institute of Microstructure Physics in Halle.