Roger Ward

Abstract:

Anisotropic and giant magneto-resistance (AMR and GMR) measurements for a molecular beam epitaxy grown (110) multilayer film [50 Å-DyFe 2/50 Å-YFe2] × 40 at 100 K are reported. The film possesses a bending field BB∼5T and an irreversible switching field BIS∼5T. These features allow the study of both AMR, and GMR caused by the creation not only of longitudinal but also transverse magnetic exchange springs, in the magnetically soft YFe2 layers. Finally, rotation experiments in applied fields show that like DyFe 2 films, there is a metastable state aligned along a [1̄ 1 0] axis at 100K. © 2004 Elsevier B.V. All rights reserved.

Abstract:

We have studied the magnetoelastic stress parameter, B ^γ,2, associated with the shear deformation within the basal plane of the (0 0 0 1) Dy (20 Å)/Sc (t = 20-60 Å) superlattices (SLs). The extrapolated B^γ,2 (0 K) values change from 1.45 to 0.9 GPa when t changes from 60 to 20 Å, respectively. All SLs show a thermal behavior of B^γ,2 affected by volume and interfacial contributions. The scandium thickness dependence of the volume contribution shows a surprisingly logarithmic behavior that indicates the existence of dislocations in the Dy blocks. © 2003 Elsevier B.V. All rights reserved.

Abstract:

Single-crystal holmium and gadolinium layers have been grown on yttrium substrates using the molecular beam epitaxy technique and their structures investigated using high resolution x-ray scattering. The experiments were performed using a Philips MRD diffractometer in Oxford, and with the XMaS facility at the ESRF. Holmium layers with a thickness below Tc′ = 115 Å give scattering that is characteristic of a pseudomorphic film structure with the same in-plane lattice parameter as the yttrium substrate to within 0.05%. For layers thicker than Tc′, there is a sharp reduction in misfit strain due to the creation of edge dislocations. The transverse lineshape of the holmium peaks exhibits a two-component lineshape for thicknesses above Tc′, but below about 500 Å. Above 500 Å the lineshape of the transverse scans becomes Gaussian and is characteristic of a mosaic crystal. The gadolinium layers show no sharp change of strain for layers as thick as 2920 Å and the transverse peak shape remained similar for all films. This is characteristic of pseudomorphic film growth and a failure to nucleate dislocations.