Roger Ward

Abstract:

The Stoner-Wohlfarth model, adapted to include magnetic exchange springs, was used to study coercivities of antiferromagnetically coupled DyFe2/YFe2 multilayer films. It was observed that coercivity rises sharply as the net magnetic moment of the superlattice approaches zero. A computational model was developed to explain the bending field, signifying the onset of a magnetic exchange spring, and the irreversible switching field, associated with magnetic reversal.

Abstract:

The resonant magnetic reflectivity from U/Fe multilayers was analyzed. These multilayers were produced through dc sputtering and analyzed using techniques such as polarized neutron reflectivity, conversion electron Mössbauer spectroscopy and magneto-optic measurements. The reversal of the polarity of the asymmetry ratio between the first and second superlattice peaks between the first and second superlattice peaks indicates a nonuniform moment distribution through the uranium layers.

Abstract:

The magnetic properties of a series of molecular beam epitaxially (MBE) grown (110) Tb1-xDyxFe2 alloy films on sapphire substrates were studied. All the measurements were performed at room temperature with the field applied along an in-plane axis. The difference between the bulk and MBE films is attributed to the presence of a magnetoelastic strain term, induced during crystal growth by the sapphire substrate.

Abstract:

Anisotropic magneto-resistance measurements for the presence of a meta-stable magnetic state in DyFe2 films were performed. The films were grown using molecular beam epitaxy. The direction of easy magnetization in the films was known to change from [001] at low temperatures to close to [351] at room temperature.

Abstract:

The magnetic ordering in CeLu alloys has been studied using neutron diffraction, and the electronic state of the Ce has been determined using X-ray magnetic resonant scattering (XMRS). CeLu orders with the same magnetic structure as Ce Y, but the temperature dependence of the order parameter is different and the average saturated moment on the Ce sites is lower. The diffuse neutron magnetic scattering observed in other Ce alloys is not observed for CeLu, and this implies that this unusual scattering originates from the competition between exchange and dipolar interactions. The XMRS results show that the Ce in CeLu alloys has an inter- mediate valence, and the results suggest that this behaviour is due to chemical pressure.