Investigating the Magnetic Manipulation of the Terahertz Radiation Emitted by Spintronic Structures

Abstract

This thesis reports on new routes for amplitude and polarisation control of terahertz (THz) radiation emitted from laser-driven spintronic THz emitters via the manipulation of the magnetisation of the structures. The spintronic structures tested are based on CoFeB/Pt bilayers and Pt/CoFeB/W trilayers fabricated by DC magnetron sputtering. Uniaxial magnetic anisotropy in the ferromagnetic film layers is enhanced and exploited leading to an experimental demonstration of full linear polarisation control of the emitted THz radiation using a varying external field applied along a hard axis of the spintronic structure. Furthermore, pre-magnetisation along an easy axis is shown to provide stable field-free THz emission from a spintronic emitter, with no reduction in signal amplitude compared to that under a saturating magnetic field. The micro-patterning of spintronic structures is examined as an alternate means of controlling the magnetisation through enhanced shape anisotropy. Micro-patterned spintronic emitters are successfully fabricated and tested, based on arrays of 2 micron x 5 micron rectangular bilayer and trilayer structures. Smooth THz amplitude control is demonstrated from rotation of patterned spintronic emitters within a fixed magnetic field. The limitations imposed by patterning due to charge confinement within the structures are examined and possible solutions using patterned ferromagnetic films on a continuous non-magnetic metallic layer are investigated.

Date of Award	26 Aug 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Darren Graham (Main Supervisor), Paul Nutter (Co Supervisor) & Thomas Thomson (Co Supervisor)