Ultrafast nanomagnets: seeing data storage in a new light.

Magnetic materials provide the most important form of erasable data storage for information technology today. The demand for increased storage capacity has caused bit sizes and features of the read-write transducers to be reduced to the nanoscale. However, increased storage capacity is only useful if there is a commensurate reduction in the time taken to read and write the data. In this article, the basic principles that determine the behaviour of nanomagnetic materials are introduced and their use in data-storage systems is described. Particular attention is paid to processes that limit the speed of operation of the data-storage system. It is shown that optical pump-probe experiments may be used to characterize dynamic magnetic processes with femtosecond temporal resolution. The macroscopic magnetization of a ferromagnet can be made to precess in response to an optically triggered magnetic field pulse, leading to reduced switching times. Alternatively, an ultrashort laser pulse may be used to manipulate the magnitude of the magnetization on femtosecond time-scales, leading to an ultrafast demagnetization in certain ferromagnets, and providing new insight into magnetotransport phenomena. Finally, the outlook for increased record and replay rates is assessed and the prospect of further use of optical techniques within magnetic data-storage technology is discussed.