NEXBIAS: New exchange bias systems for magnetic applications

The NEXBIAS RTN is concerned with the phenomena of exchange bias materials where an anti- ferromagnetic material is deposited or grown on the surface of a ferromagnetic material. In this way the magnetisation of the ferromagnet is pinned to the antiferromagnet and hence cannot reverse in the normal way. Such materials have current applications in magnetic recording read heads but also have great potential for the development of new sensor systems and particularly new solid state non-volatile memory chips devices (e.g. MRAMs) for computers. The phenomenon of exchanging biasing was discovered in the 1950s and yet, surprisingly, is not fully understood. It has recently become clear that different models of the origin of the effect are required for different materials systems. Hence it may be that more than one intrinsic parameter controls the behaviour of such systems. A problem with a complexity on this scale cannot be addressed in a single laboratory and hence collaboration is essential. The principle scientific objective of the NEXBIAS RTN is to try and establish the fundamental mechanisms of exchange biasing in a range of materials. A strong team of six academic laboratories together with an industrial partner (Siemens) forms the network. The network will fabricate a range of materials using a variety of techniques including MBE, sputtering, nanowires and fine particles to try to elucidate the fundamental origin of the exchange biasing effect. Techniques such as ion irradiation and doping with impurities will be used to distinguish between interface and bulk effects. An advanced characterisation programme involving the use of in- situ tools and ex-situ instruments extending out to the use of large experiments at central laboratories for X-ray studies will be implemented. In this way feedback will be provided to the fundamental understanding of the effect on a wide range of samples. The fully characterised materials will then be used.