The role of local versus itinerant magnetism: studies of dilute magnetic semiconductors and multi-k magnets

Lim, Joshua A. (2013). The role of local versus itinerant magnetism: studies of dilute magnetic semiconductors and multi-k magnets. University of Birmingham. Ph.D.

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Abstract

The electronic properties of the materials studied in this thesis: a dilute magnetic semiconductor and a member of the actinide family, are thought to lie on the edge of local and itinerant behaviours. The role of localised versus itinerant magnetism is indirectly explored by characterising the magnetism through a range of experimental techniques.

Reports of magnetism in dilute magnetic semiconductors have been largely conflicting, with most focusing on thin films. This work characterises high quality bulk single crystals of Cr-doped TiO\(_2\) and finds no magnetic ordering down to 4K. This suggests that the observed thin film magnetisation is a result of non-equilibrium or impurity phases and lattice strains.

In the canonical 3-k magnet, USb, the spin waves soften at a temperature, T* (well below T\(_n\)), with no change in magnetic or structural symmetries. It had been suggested that this was due to de-phasing of the different Fourier components making up the 3-k state: this was tested using inelastic polarised neutrons and found not to be the case. Instead, the effects at T* are likely linked to a change in itinerancy. The magnetic domain dynamics are probed using X-ray photon correlation spectroscopy and find changes to the domains near T\(_n\) and also T*.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):