Resolving the magnetic structure across interfaces in functional heterostructures

by Thomas Saerbeck (Institut Laue-Langevin)

Monday 2 Dec 2024, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

Nanostructured magnetic materials are at the heart of many current and future technological devices and applications, such as magnetic random access memory, magnetic sensors and quantum computing designs. Discoveries of new materials and physical properties, such as topological spin textures or long range exchange coupling in oxides, continue to fuel research efforts in nanoscale heterostructures seeking to exploit their exotic properties. A key question in materials research concerns the connection between physical properties (transport, magnetism, mechanical) and chemical as well as physical structure. This is particularly true for nanoscale materials, where the physical dimensions and interfaces are decisive in determining the physical properties. Additionally, novel phenomena may arise in heterostructures from interactions across the interface between dissimilar materials. Such proximity effects and exchange coupling are two driving mechanisms for new physics and functional behavior to emerge. Both can blur and shift the structural, electronic, chemical and magnetic boundaries independently of each other, making separate measurements of these quantities indispensable. 

Polarized neutron reflectometry (PNR) plays a dominant role in the investigation of buried layers and interfaces, which are typically difficult to access by other non-destructive techniques. In particular, PNR can resolve the magnetic moment configurations across individual layers separately from structural details, and therefore reveal interfacially driven phenomena or long range coupling mechanisms. The high sensitivity of PNR allows to identify and localize nanometer magnetic layers with sub-nanometer resolution and provides magnetizations in absolute units. Combined with complementary techniques, this depth resolved structural and magnetic profile provides insights into the underlying physical mechanisms in magnetic thin film systems. Following an overview about the technique, I will present recent investigations illustrating the sensitivity of PNR to highly localized interfacial magnetism as well as long range ordered magnetic configurations along the thickness of the sample.