Improvements in magnetic recording media density have reduced the grain size to around 8 nm at present.  At such small grain volume scales, magnetic particles can become susceptible to thermal excitation over the anisotropy barriers that stabilise the information, so that materials with higher anisotopy are required. As bit sizes are reduced so must the grain size of the particles that comprise the bits, in order to maintain good signal to noise ratios (SNR). Uniformity of particle size and shape is also important for good recording performance.

The media industry continually searches for new methods to improve the density and uniformity of magnetic particles.  One approach in which there has been some interest uses self-assembled nano particle arrays where the particles can be produced with very narrow size distributions and a well defined particle separation in the as-deposited state. Particle diameters as small as 2 nm can be produced with a size dispersion of only 5%.

Our group uses small angle neutron scattering (SANS) to measure the magnetic structure of self-assembled nanowires and nanospheres and much of this work has been carried out in collaboration with Hitachi and IBM - see ILL Scientific Highlight 2002. We are also undertaking a major new initiative within SUPA to look at the synthesis of novel nanomagnetic systems using colloidal routes. Such particles have a range of potential applications, ranging from magnetic storage and sensors through to biological assays and directed drug delivery.

References

Towards Better Recording Media,
'Neutrons and Magnetism', ILL Publication, T Thomson, S L Lee, C D Dewhurst, (2004).

Agglomeration and sintering in annelaed FePt nanoparticle assemblies studied by small angle neutron scattering and X-ray diffraction.
Thomson, T. and Lee, S.L., PRB 72 (6): Art. No. 064441, 2005.

Structural and magnetic model of self-assembled FePt nanoparticle arrays.
T.Thomson, M.F. Toney, S. Raoux, S. L. Lee, S. Sun, C.B. Murray, B.D.Terris, J. Appl. Phys. 96(2) 1197 (2004).