Designer 3D Magnetic Mesostructures

Abstract

Micro Hall probe magnetometry has been used to investigate the magnetisation of various electrodeposited microcrystals. Superconducting tin crystals of almost perfect square cuboid shapes exhibit a strong size dependence of the supercooling of the superconducting state and, for the smallest accessible crystals, the crossover to the mesoscopic regime can be readily explored close to their critical temperatures. Experimental results are in good agreement with Ginzburg-Landau simulations using the exact experimental parameters. Electroplating of the tin cores with another material provides unique core-shell structures of either two superconductors (S-S’: tin-lead) or of a superconducting core, covered with a ferromagnetic shell (S-F: tin/lead-nickel). The critical parameters of the tin core in Sn-Pb core-shell crystals are considerably enhanced and superconductivity in the tin core is detected up to 1:16 TSn c . Little-Parks oscillations in the shell can be analysed to reveal the extent of the superconducting sheath and hence can be utilised to measure the range of the proximity effect close to the critical temperature of the shell. In S-F core-shell structures, field cancellation effects govern the overall behaviour. Under certain conditions it was possible to switch the overall magnetic response from para(ferro-)magnetic to diamagnetic and back at finite applied fields. Micromagnetic simulations qualitatively reproduce the experimentally observed effects. Applications for the core-shell structures include magnetic guidance or memory devices.

Date of Award	16 Apr 2012
Original language	English
Awarding Institution	University of Bath
Supervisor	Simon Bending (Supervisor)