New Materials and Interface Effects in Charge and Spin Transport in Magnetic Heterostructures

Magnetic heterostructures are key devices for spin electronics. Their preparation requires a combination of thin film deposition with sub-angstrom control, field-annealing, and nanopatterning. If fully functional, they can help fundamental research on new materials and effects as well open applications in sensors, memory, logic, and oscillators. An introduction will present examples of basic effects and their applications. We then will discuss several novel materials and interface-induced effects occurring in magnetic heterostructures: The growth of altermagnetic thin films and their integration in magnetic tunnel junctions with barriers such as RuO₂ are at present intensively investigated due to their potentially spin-split band structure and related spin currents. X-ray analysis reveals a high crystalline quality of the films with or without twinning depending on the choice of the substrate. When integrated with an MgO tunnel barrier and a ferromagnetic counter-electrode, signatures of a tunneling magnetoresistance strongly depend on the bias voltage and are not yet fully understood. When integrated with ferromagnets (Ni₈₀Fe₂₀) or heavy metals (Pt), an analysis based on the 2ω method shows the presence of torques in accordance with a spin current at the interface. When replacing the altermagnet by a ferromagnet, the heavy metal can show a proximity-induced ferromagnetism at the interface, which substantially influences the results of well-known phenomena such as the spin Seebeck, anomalous Nernst, or anomalous Hall effects. Examples will be discussed using metallic as well as insulating ferro- or ferrimagnets and recipes for disentangling the many effects will be given.