Advances in semiconductors, permanent magnetism, magnetic recording and high frequency materials are behind much of the progress in motor and transformer technology, computers and telecommunications over the course of the twentieth and twenty first centuries. The properties are determined by the ground state, or the most energetically favourable magnetic structure or spin configuration within the material. The lifetime of the system when excited to a higher energy state also has important consequences. In practical devices, excitations constrain the characteristic timescales and lengthscales over which a non-equilibrium spin population may be controlled. In model magnetic systems, an understanding of the excitations sheds light on the underlying spin interactions.
My focus is the experimental investigation of magnetic fluctuations and magnetisation dynamics using mainly spin resonance techniques at Canada’s particle accelerator centre, TRIUMF (cmms.triumf.ca). I am focussing on four arenas, ranging from model geometrically frustrated magnetic materials to artificial heterostructures of relevance for spin transport applications.
Pure spin or angular momentum currents detected by 8Li beta detected Nuclear Magnetic Resonance (β-NMR)
Generating a spin current through spin pumping relies on the precession of the magnetisation induced in a ferromagnet excited by a radio-frequency magnetic field on resonance (FMR). The magnetisation precession is damped via the emission of a polarised spin current into the neighbouring normal metal, which is typically indirectly measured using the Inverse Spin Hall Effect (ISHE) or as an increase in the FMR linewidth. The goal is to look for direct evidence of spin pumping into the nonmagnetic layer of the heterostructures using a depth resolved probe, measuring the spin diffusion length and spin relaxation timescales. I am using 8Li β-NMR techniques at TRIUMF to look for associated changes in the local magnetic field.
