Download Half-metallic materials at the atomic scale

Half-metallic materials at the atomic scale
Lead supervisor: Ana M Sanchez
Co-supervisor: Gavin R. Bell
(Microscopy Group)
(Surface, Interface & Thin Film Group)
You will join a team of experimental and theoretical physicists investigating half-metallic
materials, which can conduct electrons with 100% spin polarisation. Our goal is to understand the
effect of low dimensionality on half-metallicity. The work will be based in Warwick but we
collaborate closely with the Universities of Cambridge and York, with Toshiba Research Europe
Ltd. and with Diamond Light Source.
The concept of half-metallic ferromagnetism was derived from the unusual band structure of the
semi-Heusler compound NiMnSb by de Groot in 1983. Over the last decade, half-metallic
ferromagnets (HMFs) have become important potential materials for spintronic applications. The
predicted 100% spin polarisation at the Fermi level is of great interest for next-generation data
storage devices, ultra-low energy spin-based logic and perhaps even quantum computation.
Half-metallicity has been predicted a number of different material systems, including semiHeusler alloys, full Heusler alloys (e.g. Co2MnSi) and oxides (e.g. Fe3O4). Successful performance
of these materials in realistic structures and technological conditions requires a detailed
understanding of not just the T = 0 spin polarisation but also the behaviour at 0 < T < TCurie and in
the presence of atomic-scale defects. Since practical devices also require thin film heterostructures,
a deep understanding of the effects of low dimensionality, interfaces and epitaxial defects on halfmetallicity is crucial. Atomic-scale characterisation is required.
Advanced aberration corrected electron microscopy and spectroscopy techniques with sub-Å
resolution will be used to determine the atomic structure of the HMF films and their interfaces with
metal, semiconductor and/or oxide substrates. Additionally, image simulations will be used to
retrieve the atomic structure from experimental data. You will concentrate on detailed
characterisations such as (1) disordering of Heusler alloys in metallic heterostructures at the unit
cell scale, (2) polymorphism and interface structures of transition metal pnictides (e.g. MnSb)
within semiconductor heterostructures, and (3) interface structures in oxide multi-layers. The
samples will be grown in York and Warwick using advanced epitaxy techniques.
The successful applicant will join the Microscopy Group and will be working very closely with
the Surface, Interface & Thin Film Group at Warwick. This PhD project provides the opportunity
to demonstrate your independence and originality, being appropriate for students who enjoy nanoscale physics at low dimensionality. The successful applicant will work in a world-leading research
area. Experimental and data analysis skills would be an advantage for this project.
Scanning transmission electron microscopy (STEM) images of MnSb/ GaAs(111) interfaces (white
arrows indicate the interface). In (a) we shown the Ga terminated GaAs(111)A face, and in (b) the MnSb
on GaAs(111)B forms with an unknown intermediate structural phase at the interface.