Summary
You will join a team of experimental and theoretical physicists investigating the interfaces between half-metallic ferromagnetic (HMF) materials and semiconductors. Our goals are to understand how atomic-scale defects and non-zero temperature affect spin-polarised transport across these crystalline interfaces so that they can be optimised for next-generation spintronic device manufacture. We collaborate closely with the Universities of York and Cambridge and with Toshiba Research Europe Ltd. Your role will be in performing and developing state-ofthe-art first-principles density functional theory (DFT) calculations, including defects and finite T effects, using high-performance computing (HPC) facilities in Warwick and York.
Background
Half-metallic ferromagnetic (HMF) materials have 100% spin polarisation at the Fermi level thanks to a spin gap straddling the Fermi level for one spin only (usually minority spin).
This property could be exploited in spin transport devices to produce, for example, high speed non-volatile memory or even configurable data processing devices. Such spintronic applications are presently hindered by the surprisingly poor performance of many HMF interfaces. The HMF state has been predicted for many materials, such as some Heusler alloys, transition metal oxides and binary transition metal pnictides (e.g. cubic B3 structure MnSb), using first-principles DFT calculations. However, typical DFT calculations neglect non-zero temperature T (hence reduced magnetisation M ) and the presence of atomic disorder and other defects. We will use state-of-the-art DFT calculations to examine realistic spintronic interfaces where such effects are explicitly included. Results from DFT will be compared to experimental data from a major experimental programme of research between York and
Warwick Universities (c. £1.5M funding): www.warwick.ac.uk/halfmetals
PhD project
You will join the Surface, Interface & Thin Film Group at Warwick. While we are mainly an experimental group we have a long tradition of using DFT for surface structure calculations. More recently, two current PhD students (with whom you would overlap by around 1 year) are working specifically on HMF surfaces and interfaces. We mainly use the highly complementary CASTEP and Munich SPR-KKR DFT codes. Through use of either large supercells (CASTEP) or the coherent potential approximation (CPA) in SPR-KKR we can calculate interfaces with realistic atomic-scale disorder. We are also able to calculate T > 0 properties through the disordered local moments (DLM) approach in CPA-KKR, in collaboration with Professor Julie Staunton of the Warwick Theory Group. Finally, we will use the calculated Bloch spectral function (BSF) with extracted band structures to calculate magneto-transport properties.
The project would suit any student with a good background in condensed matter physics: honours degree level Physics is essential, but not necessarily with a strong theoretical or mathematical bias. Experience of DFT, or computational physics and HPC more generally, would be an advantage but this is not absolutely necessary. The project is more akin to
“computer experiments”. You will need good communication and team skills to work closely with experimental scientists on our team. You would be expected to attend specialist workshops on DFT, e.g. those organised by the European Psi-K network, as well as national and international research conferences.

Figure: (top left) total energy and spin moment from T = 0 CASTEP calculation for different polymorphs of MnSb; (top right) Fermi surface of NiSb from T = 0 SPR-KKR calculation; (bottom left ) DOS for c-MnSb at T = 0 (max. M ) and T > 0 (reduced M ) from KKR-CPA-DLM calculation, showing destruction of half-metallic gap by infiltration of defect states from minority spin valence band maximum; (bottom right) predicted spin polarisation for bulk NiMnSb and c-MnSb at T > 0 from KKR-CPA-DLM method, showing the sudden collapse in polarisation at T = T *. For details see
Phys. Rev. B Rapid Comm. 85 (2012) 060403.
Teaching and support
You will be able to benefit from graduate-level teaching through the Midlands Physics
Alliance Graduate School (MPAGS) as well as specialised workshops such as the Institute of
Physics annual Magnetism course in York. We also offer the possibility of an industrial placement (extending your PhD correspondingly) and extensive training and portfoliobuilding in transferable skills, teaching and research, appropriate for both academic and industrial careers post-PhD.
Financial Support: Scholarships
There are several full or partial scholarships available for financial support. For further details please contact the Physics postgraduate admissions team and/or Dr. Gavin Bell
(Surface, Interface & Thin Film Group). You will be able to supplement grants or scholarships by paid teaching duties in Physics. Options include:
 Doctoral training grant (normally UK students only, EU students may be elibigle)
 Chancellor’s International Scholarship (overseas students: highly competitive)
 China Scholarships Council (Chinese students only)
 Overseas national government scholarships (we would be happy to support applications e.g. for Commonwealth scholarships)