Magnetoresistive sensors for magnetic domain wall technologies

Recent developments in magnetic nanotechnology have seen new device concepts emerge that could challenge traditional silicon-based microelectronics in certain applications. A key advantage of magnetic devices over alternative technologies is that they generally do not require power to retain data. In specific cases, magnetic nanotechnology devices may also offer higher device density, lower power consumption, improved reliability or additional functionality compared with their rivals. Some of these magnetic devices are made using thin ferromagnetic layers separated by a non-magnetic metal spacer layer just a few atoms thick. The upper and lower layer will have different magnetisation directions and the electrical resistance of the overall device depends on their relative orientation due to an effect known as 'giant magnetoresistance' (GMR). Already, these devices are widely used as magnetic field sensors in many applications, e.g. in computers and automotive products. Other technologies are being developed based upon networks of planar magnetic nanowires, usually with just a single magnetic layer and no spacer layers. The geometry of the wires is important, since this restricts magnetisation to lie in one of two directions along the wire axis. This provides a simple system for representing the binary numbers of digital information. Opposite magnetisation directions can meet, and where this happens, they are separated by a transition region known as a 'domain wall'. Domain walls can be easily created or removed and made to propagate through a nanowire network using magnetic fields or electrical currents in the nanowires. In this way, information is written, deleted and sent through a circuit, be it a sensor, memory or logic device. However, for these devices to be commercially successful, we must have read-out of the magnetic data in form compatible with modern electronics. There have not been any demonstrations of this to date. In this collaborative research programme, we will address this deficiency by developing a nanoscale device to read data in magnetic nanowires. Our recent calculations have shown that the magnetic field from domain walls is very high close to the nanowires. We will use this field to change the magnetic configuration of a nearby sensor and detect these changes using GMR. This will be a significant step for magnetic nanowire technologies since it will allow nanowire devices to be fully integrated as stand-alone integrated circuits. We will also use these sensors for scientific measurements to improve our understanding of the behaviour of domain walls in magnetic nanowires.The applicants for this project bring together world-leading experience in nanofabrication, magnetic nanowires, GMR materials and computer modelling of nanoscale magnetic systems, making this the ideal team to undertake such a challenging project.