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Structural and magnetic properties of holmium-scandium alloys and superlattices

BrynJacobsen, C; Cowley, RA; McMorrow, DF; Goff, JP; Ward, RCC; Wells, MR; (1997) Structural and magnetic properties of holmium-scandium alloys and superlattices. PHYS REV B , 55 (1) 317 - 329.

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Abstract

The properties of Ho-Sc alloys and superlattices grown by molecular-beam epitaxy have been investigated using x-ray and neutron-diffraction techniques. Structural studies reveal that the alloy samples have different a lattice parameters for the Sc-seed layer and the Ho:Sc alloy grown on top of the seed layer; while the superlattices have different a lattice parameters for the Sc seed, and for both the Ho and Sc in the superlattice layers. The structural characteristics are related to the large lattice mismatches (of the order 7%) between the constituent elements. The magnetic moments in the alloys form a basal-plane helix at all temperatures, with distortions of the helical arrangement for samples with the highest Ho concentrations. The dependences of the Neel temperature, T-N and the helical wave vector upon both temperature and concentration are compared with those of other alloy systems. It is found that a good description of the dependence of T-N upon concentration is given by a virtual-crystal model where the peak in the conduction-electron susceptibility varies linearly between that of the pure constituents. In the superlattices, the moments also form a basal-plane helix at T-N. In this helical phase, some samples exhibit a short-range coherence of an antiferromagnetic coupling between adjacent Ho blocks. For one superlattice, there is a low-temperature transition to a ferromagnetic phase, in which moments are ferromagnetically aligned within Ho blocks, and coupled antiferromagnetically between adjacent Ho blocks. The contrast with systems which have Y or Lu as the nonmagnetic element is discussed in terms of the structural properties of the samples, band-structure calculations, and the possible influence of dipolar forces.

Type: Article
Title: Structural and magnetic properties of holmium-scandium alloys and superlattices
Keywords: RARE-EARTH SUPERLATTICES, GD-Y SUPERLATTICES, YTTRIUM, SUSCEPTIBILITIES, METALS, ORDER
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/60100
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