Roger Ward

Abstract:

The magnetic structure of Laves phase superlattices of structure [70/30]60, [150/100]50 and [50/70]60 were discussed. It was found that the [50/70]60 sample showed unexpected behavior because the moments aligned largely perpendicular to an applied field. The net moments on the DyFe2 and YFe2 layers were also discussed.

Abstract:

The temperature dependence of the internal field in the one-dimensional S = 1 chain compound LiVGe2O6 has been measured using muon-spin rotation. Two muon-spin-precession frequencies are observed, corresponding to two distinct stopping sites. The results demonstrate that LiVGe2O6 undergoes a second-order phase transition to long-range magnetic order at TN = 24.5 K. In the paramagnetic regime, we find exponential muon-spin relaxation which is dominated by fluctuations of the ⁵¹V nuclear moments. © 2003 The American Physical Society.

Abstract:

The chemical structure of epitaxial γ cerium and the chemical and magnetic structures of cerium/neodymium superlattices have been studied using x-ray and neutron diffraction techniques. The samples were grown using molecular-beam epitaxy, optimized to yield the desired Ce allotropes. The x-ray measurements show that, in the superlattices, both constituents adopt the dhcp structure and that the stacking sequence remains intact down to T 2 K; these are the first measurements of magnetic ordering in single-crystal dhcp Ce. The magnetic structure of the superlattices with thicker Nd layers exhibit incommensurate order and ferromagnetism on separate sublattices in a similar manner to Nd under applied pressure. The sample with thickest Ce layers has a magnetic structure similar to bulk β Ce, which has commensurate transverse modulation with a propagation wave vector [1/2 0 0] and moments along the hexagonal a direction. These two types of magnetic order appear to be mutually exclusive. γ Ce is the high-temperature fcc phase of Ce, our single-phase epitaxial sample is observed to go through a new, but partial, structural transition not previously seen in the bulk material. © 2003 The American Physical Society.

Abstract:

The magnetic field-induced degradation of magnetic properties in molecular beam epitaxy grown FeMn/NiFe exchange-coupled bilayers was discussed. When the samples were subjected to several magnetic sweeps, there was blister-shaped deterioration of the film surface quality and the magnetometry data suggested an increasing fraction of the NiFe moments. Analysis showed further degradation could be attributed to the formation of the nonmagnetic FeMn oxide by oxidation of the bare FeMn.