Roger Ward

Abstract:

Molecular beam epitaxial methods have been used to grow single crystal Laves phase DyFe2/YFe2 superlattice samples with a (110) growth direction. In particular, the magnetic properties of the YFe2 dominated multilayer samples [wDyFe2/4wYFe2]XN with w=20, 30, 40, 45, 50, and 55 Å are presented and discussed. In principle, the multilayer films should possess similar magnetic properties because they are all nominally Dy0.2Y0.8Fe2. However, it is shown that their magnetic properties depend strongly on the thickness of the DyFe2 layers w. Those films with w≥45 Å possess negative coercivities, while those with w≤40 Å are positive. It is argued that this behavior can be understood in terms of a strong increase of the intrinsic coercivity of the DyFe2/YFe2 superlattice, taken as a whole, as w is reduced. For w≤40 Å almost none of the DyFe2 moments can be flipped over in the available field range (12 T). © 2001 American Institute of Physics.

Abstract:

Molecular beam epitaxial methods have been used to grow single crystal Laves phase DyFe2/YFe2 superlattice samples with a (110) growth direction. Detailed magnetization curves have been obtained for YFe2 dominated multilayer samples [wDyFe2/4wYFe2]× 16 with w=45, 50, and 55 Å. In particular, it is shown that the formation of magnetic exchange springs in the magnetically soft YFe2 layers, can be used to engineer multilayer samples with a negative coercivity. Further, by using asymmetric field cycling procedures, we have investigated the irreversible parts of the M-B loop, associated with the switching of the DyFe2 multilayers. © 2001 American Institute of Physics.

Abstract:

The chemical and magnetic structure of Cerium/Neodymium superlattices grown by molecular-beam epitaxy have been determined using x-ray and neutron diffraction techniques. The x-ray studies show that both constituents adopt the dhcp structure, and that the stacking sequence is coherent over many bilayer repeats. The dhcp structure remains intact down to T ∼ 2K; these are the first measurements of magnetic ordering in single-crystal dhcp Ce. The magnetic structure of the samples with thicker Nd layers exhibit incommensurate order and ferromagnetism on separate sublattices in a similar manner to Nd under applied pressure. The superlattice with thickest Ce layers has an incommensurate magnetic structure similar to that predicted for bulk dhcp Ce. These two types of magnetic ordering appear to be mutually exclusive.

Abstract:

The coercivity of MBE-grown Laves-phase DyFe2-YFe2 thin-layered (≤ 50 Å) superlattice samples, with a (110) growth direction, can be varied by adjusting the relative thickness of the YFe 2 and DyFe2 layers. However, for sufficiently thick layers, the coercivity is found to be dependent on the thickness of the YFe 2 layers, even when the ratio of DyFe2/YFe2 is fixed. This feature is illustrated using the superlattice films [wDyFe 2/wYFe2] x 40, with, w = 75, 100 and 150 A. The underlying reason for the decrease in coercivity with increasing width w, is traced to the action of the magnetic exchange springs in the YFe2 layers. © 2001 Elsevier Science B.V. All rights reserved.