Development of new CuMn-V epitaxial antiferromagnetic semiconductors for applications in spintronics

This proposal aims to develop new room-temperature antiferromagnetic semiconductor thin films which are compatible with mainstream electronics while offering unique spin-based functionalities.

Systems combining the logic functions of semiconductors with the sensing and storage capabilities of magnetic materials are highly sought-after as building blocks for a new generation of fast, non-volatile and high-density electronic devices.

In principle magnetic semiconductors offer many advantages over both magnetic metals and non-magnetic semiconductors for such applications, but despite major efforts over more than 10 years room temperature ferromagnetic semiconductors have still not been convincingly demonstrated.

It has recently been predicted that exciting new functionalities can be realized using antiferromagnetic materials. In an antiferromagnet, electron spins on adjacent atomic sites are aligned anti-parallel to each other, so that the net magnetic polarization is zero. These staggered electron spins offer an alternative mechanism for the storage and sensing of information. This greatly enhances the prospects for technological applications of magnetic semiconductors, as there are several candidate materials with antiferromagnetic spin order at room temperature, at least in bulk form.

We are proposing to develop high quality thin films from two materials, CuMnAs and CuMnP, identified as having the highest potential for room temperature applications based on antiferromagnetic spin order. Materials will be produced by molecular beam epitaxy, an established method for growing single crystal thin films which is widely used in the semiconductor industry.

We will identify the optimal conditions for producing ordered single-phase films and will develop methods for producing n- and p-type doping. The structural, electrical and magnetic properties of the films will be investigated using a range of approaches.

The proposed materials development programme will provide a solid foundation to establish within the UK a strong research activity in antiferromagnetic semiconductor spintronics.

The development of new materials is central to the introduction and development of new technologies. With this proposal we aim to investigate two materials never before synthesized in thin-film form, and take the first steps towards determining their viability as the building blocks for beyond-CMOS technology. While this proposal is predominantly focussed on spintronics, the materials themselves may find applications in other areas, such as energy harvesting and storage, optoelectronics, microwave technology, or quantum information processing. We are unaware of any other research programmes, either nationally or internationally, focussed on the thin film growth of the CuMn-V materials, thus the possibility for impact as an important 'world-first' is high.

More specifically, the development of new antiferromagnetic semiconductors, with tuneable electrical and magnetic properties and compatibility with existing microelectronics technology, will broaden and deepen the prospects for spintronics as a new paradigm in information processing. The exchange-bias of a ferromagnet by these materials opens an immediate research opportunity for integrating conventional semiconductor functionalities directly within the exchange pinning layers in common spintronic devices. Furthermore, it has recently been demonstrated that, by utilizing the exchange spring effect to control the staggered AFM moment orientation in ferromagnet-antiferromagnet bilayers, magneto-resistance effects exceeding 100% at fields below 50mT can be realized in tunnelling from an antiferromagnetic layer in a spin-valve stack. This effect has its origin in the spin-orbit induced density-of-states anisotropy in the antiferromagnet. Relativistic ab initio calculations have indicated that even larger tunnelling magnetotransport anisotropy (eg, 10 to 100 times larger density of states anisotropies than in the antiferromagnetic metal IrMn) should be realizable in CuMn-V materials, which in addition have the possibility of control by doping or electrical gating.

Antiferromagnetic spintronics is a young and rapidly developing field with much untapped potential. The primary deliverable of this research programme will be a unique source of well-characterized, high quality antiferromagnetic semiconductor thin films and heterostructures which will be made available to the UK research community. This will put the UK at the forefront of this emerging field, stimulating further research and providing a solid foundation for the development of new spin-based devices and technologies, of direct and lasting benefit to the UK's economic competitiveness.