Neutron and Muon Studies of Spin Dynamics in Magnetic Systems

In this thesis I present an investigation on the spin dynamics observed during moment localisation, non-ergodic magnetic phase transitions, and weak itinerant electron magnetism.

The pseudo-binary compound Y(Mn1-xAlx)2 has been investigated under the influence of equivalent opposing chemical and mechanical pressures using Muon Spin Relaxation. The results reveal the application of external mechanical pressure (4.5kbar) to destabilise the manganese moment, and produce a ground stte distinctly different to that seen under ambient pressure conditions. Short-range nuclear and spin correlations have been studies via diffuse neutron scattering, and through a combination of analysis techniques I have mapped the temperature dependence of these correlations and their evolution due to the substitution of manganese for aluminium.

Applying new methods of hierarchical relaxation and non-extensive entopy I have studied the slow relaxation dynamics of the spin glass phase using Beutron Spin Echo spectroscopy. The results are dveloped further by applying the same analysis to a variety of glassy magnetic phenomena: spin glass freezing ((La1-xEr x)Al )Al2), and superparamagnetic blocking (Cr 1-xFe x). I have shown that within this framework the underlying freezing mechanisms result in distinctly different responses, and that in the case of spin glass relaxation an apparantly universal scaling relationship is present.

Finally the results of a Muon Spin Relaxation study on the moment fluctuations in Au4V above the Curie temperature are reported. The temperature dependence of the muon spin relaxation rate is to be similar to that of the archetypal weak itinerant helimagnet, MnSi.