Inter-elemental Exchange Mechanisms in Complex Magnetic Materials

Magnetism arising from the interplay of different magnetic species is a topic of special relevance, especially when looking at the design of device heterostructures and other complex magnetic materials. In this proposal we aim to study the magnetism in two classes of materials by XAS and XMCD. Co3-xNixSn2S2 is a material class with a complex Kagome crystal structure showing peculiar magnetic properties upon Ni-doping, namely an increase in coercive field with decreasing critical temperature. We here aim to individually address the magnetic moment on the Co, Ni and Sn sites trying to unravel the role of the individual elements in the collective magnetic behaviour. MnBi2Te4 – (Bi2Te3)n – Cr2Ge2Te6 /Fe3GeTe2 are heterostructures grown by MBE, coupling a magnetically extended topological insulator to a high-Tc ferromagnetic substrate. Already in previous experiments we have found a strong coupling between the 2D ferromagnetic Mn lattice and the Fe-based substrate, whose nature changes with the thickness of an intermediate non-magnetic TI. Extending this to the ferromagnetic Insulator Cr2GeTe6 poses the next step towards utilizing these heterostructures in device design by controllably switching single magnetic layers against each other. Taken together both material classes aim to understand the coupling between different magnetic elements in a structure either by incorporation in the same crystal lattice or their coupling over an material interface. Our experiments crucially depend on the element- as well as surface-sensitive nature of the XMCD experiment, allowing us to individually address different magnetic atoms and probe contributions from monolayers placed on top of a crystal surface.