Thermal behaviour of nanostructured magnetic materials

Abstract

With the ever-increasing need to fit memory storage into a smaller space, technological solutions are utilising heat to allow data to be written into hard drives with extremely high coercivity. The purpose of this thesis is to explore and understand the thermal behaviour of magnetic materials that have been strategically nano-structured. The exploration diverges into three parts: firstly, the effect of magnetic domain direction, parallel and perpendicular to the direction of heat flow, has on the thermal transport, see chapter 3. This devolved into using magnetic and thermal simulations to estimate the required minimum thermal conductivity ratio of parallel to perpendicular domains, for the Scanning Thermal Microscope probe to resolve. Secondly, the relationship between thermal and exchange energy of Manganese perovskites were explored by isothermal magnetisation vs applied field measurements, carried out using a superconducting quantum interference device, see chapter 4. The perovskites were doped with various amounts of Calcium, and synthesised in various environments to observe this would alter the magnetocaloric effect of the perovskites. Lastly, the phenomenon of spin cross-over (SCO) in similar Manganese complexes were contrasted and compared. Magnetisation vs temperature measurements, coupled with X-ray diffraction characterisation of the molecules before and after the transition temperature, allowed insight into the cooperativity mechanism. The cooperativity of a crystal lattice is what allows for sharp SCO transitions exhibiting hysteresis. Molecules with this form of SCO transition are suitable candidates for memory storage.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering and Physical Sciences Research Council & Seagate Technology LLC
Supervisor	Solveig Felton (Supervisor) & Robert Bowman (Supervisor)