My research interests focus around the investigation of spin dependent electronic transport in solid state materials, with special reference to the questions arising from the emerging technology of spin-electronics (spintronics). Broadly, my research is split into two themes; (1) synthesis of new materials with novel spintronic properties to further understanding of spin transport phenomena and search for new spintronic materials and (2) characterization of electronic transport in thin film spintronic devices, to investigate the potential of various semiconductor and ferromagnetic materials systems for device applications. I am also affiliated to Experimental Solid State Physics, Imperial College London and many of the transport measurements are carried out there. Some specific areas are:

Chemical control of the anomalous Hall effect: In ferromagnets, the anomalous Hall effect (AHE) gives an extra component to the normal Hall effect proportional to the magnetization. Recently, spin was proposed as a cause of AHE, but this remains a controversial proposal. Understanding the mechanism of AHE will allow both intelligent design of new AHE materials and the development of AHE as a direct probe of spin transport in ferromagnets. Nd 2 Mo 2 O 7, a "ferromagnetic spin ice" naturally selects one spin chirality. Chemical substitution is being used to investigate the roles of spin chirality and spin dependent scattering in the ferromagnetic spin ice. (Part of this research is in collaboration with Prof. S.T. Bramwell , Dr M. A. Green and Dr A. S. Wills.
Studying transport spin polarization in spintronic devices: The spintronics revolution promises dramatically improved performance over conventional electronics. However, it has proved to be technologically challenging to inject, manipulate and detect spin polarized currents in semiconductor devices. The transport spin polarization of candidate spintronic ferromagnets is evaluated with transport measurements, in particular the Anomalous Hall Effect and Point Contact Andreev Reflection Spectroscopy. The anomalous Hall effect is a direct consequence of the natural polarization of the conduction electrons in ferromagnets, and it is being used to investigate the spintronic properties of thin ferromagnetic films. Particular emphasis is placed on the interfaces between ferromagnetic and semiconducting layers. This work is carried out in collaboration with Dr L.F.Cohen, Imperial College London.

Selected publications: (for a full publication list please click here)

Y. Bugoslavsky, Y. Miyoshi, S. K. Clowes, W. R. Branford, M. Lake , I. Brown, A. D. Caplin, and L. F. Cohen, " Possibilities and limitations of point-contact spectroscopy for measurements of spin polarization " Physical Review B 71, art. no.-104523 (2005).
W. R. Branford, S. K. Clowes, M. H. Syed, Y. V. Bugoslavsky, S. Gardelis, J. Androulakis, J. Giapintzakis, A. V. Berenov, S. B. Roy, and L. F. Cohen, " Large Positive Magnetoresistance in non-stoichiometric NiMnSb thin films on silicon " Applied Physics Letters 84, 2358 (2004).
W. R. Branford, S. K. Clowes, Y. V. Bugoslavsky, S. Gardelis, J. Androulakis, J. Giapintzakis, C. E. A. Grigorescu, S. A. Manea, R. S. Freitas, S. B. Roy, and L. F. Cohen, " Thickness dependence of Hall transport in Ni1.15Mn0.85Sb thin films on silicon " Physical Review B 69, art. no.-201305 (2004).
W. R. Branford, S. K. Clowes, Y. V. Bugoslavsky, Y. Miyoshi, A. V. Berenov, J. Rager, S. B. Roy, J. L. MacManus-Driscoll, and L. F. Cohen, " The Effect of Chemical Substitution on the Electronic Properties of Highly Aligned Thin Films of Sr2-xAxFeMoO6 (A=Ca, Ba, La; x=0, 0.1) " Journal of Applied Physics 94, 4714 (2003).
W. Branford, M. A. Green, and D. A. Neumann, " Structure and ferromagnetism in Mn4+ spinels: AM(0.5)Mn(1.5)O(4) (A = Li, Cu; M = Ni, Mg) " Chemistry of Materials 14, 1649-1656 (2002).

This page last modified 30 August, 2010