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CMP
Credit: Jack Hobhouse

Roger Ward

Retiree

Sub department

  • Condensed Matter Physics
Roger.Ward@physics.ox.ac.uk
Telephone: 01865 (2)72271,01865 (2)72355
Clarendon Laboratory, room 164
  • About
  • Publications

Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

Scientific Reports Nature Publishing Group 4:1 (2014) 7277

Authors:

D Li, Ma, S-G Wang, Roger Ward, Thorsten Hesjedal, X-G Zhang, A Kohn, E Amsellem, G Yang, J Liu, J Jiang, H-X Wei, X Han

Abstract:

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.
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Direct evidence of the anisotropy of magnetization in rare-earth metals and rare-earth/Fe2 alloys

Physical Review B American Physical Society (APS) 90:5 (2014) 054407

Authors:

L Benito, K Dumesnil, RCC Ward
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Ultrafast optical parametric pumping of magnetization reorientation and precessional dynamics in DyFe2/YFe2 exchange springs.

Physical review letters 113:6 (2014) 067601

Authors:

LR Shelford, Y Liu, U Al-Jarah, PAJ de Groot, GJ Bowden, RCC Ward, RJ Hicken

Abstract:

The magnetization dynamics of a wound [DyFe(2)(20  Å)/YFe(2)(80  Å)](×40) exchange spring multilayer have been explored in optical pump probe experiments. Ultrafast optical heating was used to modify the magnetic parameters of the multilayer, while the time resolved magneto-optical Kerr effect was used to probe its response. Although the probe signal is dominated by precession and winding of the exchange spring within the soft YFe(2) layer, reorientation of the DyFe(2) hard-layer magnetization is detected on time scales less than 100 ps. Micromagnetic simulations reproduce the main features of the experimental data and indicate a dramatic optically induced reduction of the hard-layer anisotropy. The results establish the feasibility of switching a spring system by means of parametric excitation.
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Malleability of uranium: Manipulating the charge-density wave in epitaxial films

Physical Review B American Physical Society (APS) 89:24 (2014) 245101

Authors:

R Springell, RCC Ward, J Bouchet, J Chivall, D Wermeille, PS Normile, S Langridge, SW Zochowski, GH Lander
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In-plane uniaxial magnetic anisotropy induced by anisotropic strain relaxation in high lattice-mismatched Dy/Sc superlattices

Physical Review B American Physical Society (APS) 89:13 (2014) 134421

Authors:

L Benito, C Ballesteros, RCC Ward
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