Roger Ward

Abstract:

Spin-polarised neutron reflectometry has been used to investigate a magnetic exchange spring, formed in a (75Å DyFe2/150Å YFe2) × 18 multilayer thin film. The existence of an exchange spring is found to enhance the level of neutron spin flipping during reflection, a strong indicator of the formation of transverse magnetic moments within the YFe2 layers. © 2003 Published by Elsevier B.V.

Abstract:

Magnetic multilayers are known to have behaviour shaped by the intrinsic magnetic properties of their constituents and of their interactions. Multilayers composed of Uranium (5f electrons) and transition metal (3d electrons) provide the unique combination of a potentially large orbital moment with strong electronic hybridisation effects between the extended 5f states and the strongly magnetic 3d states. In this study U/Fe multilayers with layer thicknesses 20ÅIV edge using different geometries of circular polarisation helicity and applied magnetic field. Some evidence of U moments has been observed. © 2003 Elsevier B.V. All rights reserved.

Abstract:

A vector vibrating sample magnetometer has been used to determine the direction of easy magnetisation in a thin film of DyFe2. The 4000 Å thick film, with a [110] growth direction, was prepared using molecular beam epitaxy. The results show that the direction of easy magnetisation is temperature dependent. At 4K this direction corresponds to the [001] type axes. But at 290K, the easy axis is close to a [1̄10] direction, but pointing out of the plane of the film at angle of ∼(14±3)°. On the basis of the vector magnetometer results at 290K we find two easy magnetisation axes close to [3̄50] or [5̄30] (and opposite directions). Finally, it is shown that DyFe2 films are unique in that the remanent magnetisation can be manipulated to point either in or out of the plane of the film. © 2003 Elsevier B.V. All rights reserved.

Abstract:

The basal plane magnetoelastic stress, B^γ,2, of Dy 16/Ho22, Dy14/Lu30 and Dy 21/Lu11 (0001) superlattices is investigated. For Dy 16/Ho22 we obtain B^γ,2 (12 T, 0 K) = 0.4GPa, while for Dy21/Lu11 and Dy21/Lu 11 it amounts 0.33 and 0.9 GPa, respectively. In the first case, the value obtained is explained in terms of the known values of B ^γ,2 for bulk Dy and Ho, including small interface and strain contributions, whereas in the Dy/Lu samples, B^γ,2 have large non-bulk contributions. The differences in epitaxial compression and in electronic structure for both kind of superlattices can explain these results. © 2004 Elsevier B.V. All rights reserved.

Abstract:

At room temperature, ⁵⁷Fe Mössbauer studies suggest that the easy axis in MBE grown (1 1 0) DyFe2 films is [3̄ 5 1]. Whereas vector vibrating sample magnetometer investigations indicate [3̄ 5 0]. But both agree that the easy axis points at some 14° out of the plane of the film. In this paper, we give theoretical expressions for (i) the energy stability of the [ū v 0] axis, (ii) the field required to pull the magnetization back into the [1̄ 1 0] plane of the film, and (iii) energies of the [ū v 0] and [0 0 1] axes. These expressions are used to derive values for the fourth order crystal field and the magneto-elastic strain term. © 2004 Elsevier B.V. All rights reserved.