Roger Ward

Abstract:

The structure and magnetism of epitaxial thin-film dysprosium-praseodymium and erbium-praseodymium alloys with the double-hexagonal close-packed (dhcp) crystal structure have been investigated. Short-range atomic and magnetic order have been found for DyxPr1-x with 0.4 ≥ x ≥ 0.05 and ErxPr1-x with 0.2 ≥ x ≥ 0.05. The distribution of the two species within the alloys was established with x-ray and neutron diffraction techniques. The atomic order is complex; the four planes of the unit cell have differing concentrations of constituents. In addition there are occasional clusters within the close-packed planes. The magnetic behaviour was investigated using neutron diffraction. Surprisingly, only short-range order is observed in the dhcp-structure alloys. Magnetization measurements suggest that Dy0.13Pr0.87 exhibits spin-glass behaviour. The roles of the indirect exchange interaction, the dipole-dipole interaction and the crystal field are considered in detail.

Abstract:

A report on the magnetization and magnetoresistance measurements for antiferromagnetically coupled DyFe2/YFe2 multilayers was presented. The formation of short range springs in the magnetically soft YFe2 layers was demonstrated which resulted in giant magnetoresistance. Both the magnitude of the effect and its dependence on magnetic field were found to be in good agreement with the theory of Levy and Zhang for domain wall induced giant magnetoresistance.

Abstract:

We report on zero field cool susceptibility (χZFC), magnetization (M) and magnetoelastic stress (MELS) measurements, in the range 8-200 K and up to 12 T applied magnetic field, on (0001) superlattices [Ho15/Dy30]50 and [Ho30/Dy15]50. Magnetic phase diagrams are proposed, with a wide variety of magnetic phases: paramagnetic, helical, helifan, fan and ferromagnetic. Same magnetic phases for Dy and Ho coexist. Exchange polarization of Ho layers by Dy ones is manifested. Although compressed by basal plane a-lattice parameter misfit, spontaneous ferromagnetic order in Dy layers is suppressed, as well as ferro-cone phase in stretched Ho ones. However, modest applied magnetic field along b-axis (H≅0.6 T, at 10 K) produces ferromagnetic order in Dy (in basal plane) and ferro-cone in Ho. The basal plane hexagonal symmetry breaking magnetoelastic stress M^γ,2 (T = 0, 12 T) is separated for Ho and Dy layers, in good agreement with single-ion magnetoelastic coupling model. © 2001 Elsevier Science B.V. All rights reserved.