Probe, correlate and understand magnetism, superconductivity, and phonons at the nanoscale (invited talk)

Probe, correlate and understand magnetism, superconductivity, and phonons at the nanoscale Margriet J. Van Bael1, Kristiaan Temst2, André Vantomme2 1Laboratory of Solid State Physics and Magnetism, KU Leuven, Belgium 2Instituut voor Kern-en Stralingsfysica, KU Leuven, Belgium When reducing the dimensions of metals down to the nanometer regime, quantum confinement effects result in pronounced deviations of the electronic, magnetic, and optical properties compared to the bulk behavior. In the field of magnetism, thin films and patterned structures allow a real tuning of the magnetic parameters by altering thickness, crystallographic orientation and shape, which affect the anisotropy parameters. Recently, this research area has seen major new developments like spin torque transfer, skyrmion lattice phases, dilute (ferro)magnetic semiconductors and spintronics based on antiferromagnetic semiconductors. The interface turns out to play a crucial role in multiferroic composite structures, where ferromagnetism and ferroelectricity are confronted with each other, in some cases leading to exciting new magnetoelectric coupling effects. Regarding electronic properties, fundamental studies of phase formation in silicides and germanides are carried out, with the aim of better understanding the interface between an electronic device and the ‘outside world’. Also the properties of atomic vibrations (phonons) are strongly affected by nanoscale confinement. Phonons influence many material properties, such as thermal and mechanical behavior. Furthermore, the electron-phonon interaction lies at the heart of Cooper-pair formation and is therefore of crucial importance in super¬conductivity. The phonon density of states directly determines key superconducting parameters such as the electron-phonon coupling strength and the critical temperature. There remains however a clear need for improving our fundamental understanding of the phonon related properties for materials with reduced dimensionalities, in particular because atomic vibrations are difficult to access at this scale. Our general aim is to understand how the size and structure of nanoscale objects, (thin films, nanowires, nanoparticles, …) affect their magnetic, superconducting and phonon properties. Moreover, it is of particular interest how magnetism, superconductivity and phonons mutually influence each other. New challenges are tackled in probing these functional properties at the atomic or nanoscale level, e.g., by using isotope specific techniques such as nuclear inelastic scattering of synchrotron radiation to probe the phonon properties or nuclear resonant scattering to probe the local magnetic ordering, while polarized neutron reflectivity allows to obtain magnetic depth profiles. Such local magnetic probing to complement more conventional SQUID-based magnetometry provides key information for understanding the magnetic ordering and phenomena at surfaces and interfaces in multiferroics, magnet/superconductor hybrid systems, etc. A number of representative PhD projects will be presented that are jointly carried out at the Laboratory of Solid State Physics and Magnetism and the Instituut voor Kern- en Stralingsfysica at KU Leuven. The main research infrastructure for sample fabrication and characterization, such as the Ion and Molecular Beam Laboratory, will be illustrated as well as the main methods for measuring phonon, magnetic and electronic properties, alongside with structural characterization.status: publishe