Exploring tunable magnet/superconductor hybrid quantum systems via spin-polarized low energy electron microscopy
Final Report Abstract
Spin-polarized low energy electron microscopy (SPLEEM) is an imaging technique which has been employed for the investigation of nanometric scale spin textures in magnetic thin films and multilayers with great success in the last decade. SPLEEM is an experimental technique which allows for the imaging of the full 3-dimentional (3D) spin texture of magnetic thin films. Given the fact that SPLEEM relies on the different probability of backscattering of spin polarized electrons, it requires the imaged magnetic films to have a high crystallographic order. This makes SPLEEM a unique microscopy technique for the investigation of epitaxial magnetic thin films and multilayers grown on single crystal substrates, which combines nanometric spatial resolution with 3D spin mapping. The scope of this project was twofold: 1. the discovery of magnet-superconductor hybrid systems hosting non-collinear spin textures; 2. the investigation of the influence of the superconducting phase transition on the magnetic ground state of the hybrid system. Magnetsuperconductor hybrid systems (MSHs) are heterostructures where magnetic thin films and multilayers are in direct proximity with a superconducting substrate. In this project, niobium (Nb) was the superconductor of choice, being the elemental superconductor with the highest critical temperature, TC = 9.2 K. Given the interest in investigating MSHs at room temperature as well as at low temperatures, we decided to perform our experiments at the low-temperature SPLEEM available at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, California. This is a microscope equipped with a flow cryostat, which is in principle capable to work at temperature as low as 7-8 K. The hope was to be able to investigate the prepared MSHs at T > TC as well as T < TC. During the two experimental sessions at LBNL – each one being two weeks long – we were successful in developing a recipe for the grown of an epitaxial magnetic multilayer on the oxygen-reconstructed surface of a Nb(110) single crystal. The prepared [Ni/Co]n multilayer was engineered so to host a magnetic ground state with out-of-plane anisotropy. However, the effect of the transition into the superconducting phase was not investigated due to the fact that the SPLEEM system is not yet capable of reaching temperatures lower than the TC of the Nb crystals.
