Development of MBE grown CrSe for spintronics applications

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Electrons are particles which have spin as well as charge, and like charge the orientation of the spin can be used to store and transport information. This has given rise to the rapidly developing area of spintronics. Currently the successful spintronic devices are all based on structures which contain alternating layers of magnetic and non-magnetic metals, and to date there have been considerable problems in developing successful spintronic devices containing semiconductors.Such devices require a magnetic material which can form a junction with a semiconductor to selectively either inject or remove electrons with one particular spin orientation. Ideally, the material should work well at room temperature, not react chemically with the semiconductor and only inject one spin orientation. To date there is no material with fulfils all three criteria.Half metals are types of magnetic material which have attracted considerable interest as potential semiconductor contacts. In a half metal, the bands for the two different spin electrons have quite different energies, so that the Fermi energy lies above the bottom of the Conduction Band for one spin orientation, but is below it for the other. For the first spin orientation the material behaves as a metal, while for the other it demonstrates all the typical semiconducting features, such as a bandgap.Recently it has been shown that compounds of certain transition metals with elements from group V or VI of the periodic table are half metallic when grown in the zinc blende crystal structure, which also means they can be grown as part of multilayer structures with more conventional semiconductors. However all of these compounds do not normally grow in this crystal structure which means that they have to be grown in a higher energy, metastable form.In this proposal we have identified one of the most promising of these materials, which is the compound chromium selenide. This has many attractive properties and should satisfy all three criteria for a good contact material.Despite this, zinc blende CrSe has never been grown before. The aim of this proof of principle proposal is to demonstrate that CrSe can be grown in the zinc blende crystal structure by molecular beam epitaxy (MBE). The structural properties (lattice constant, Poisson's ratio, etc) will be measured at Heriot-Watt University and samples will also be provided to Prof. Wolfram Heimbrodt at Philipps Universitaet, Marburg who will provide a basic assessment of the magnetic properties of the layers.If this proposal demonstrates that CrSe can be produced with the zinc blende crystal structure and, as predicted thin layers are ferromagnetic above room temperature, then a subsequent full proposal will then be produced which will aim to exploit the properties of CrSe in a range of spintronic devices.