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D. Süss, T. Schrefl, R. Dittrich, M. Kirschner, F. Dorfbauer, G. Hrkac, J. Fidler:
"Exchange spring recording media for areal densities up to 10 Tbit/ine²";
Journal of Magnetism and Magnetic Materials, 290-291 (2005), 551 - 554.

In order to achieve an areal density of 10 Tbit/in2 in perpendicular recording, grains with diameters of about 3 nm are required. However, for such grain sizes, common hard disk materials are magnetically too soft to be thermally stable. Extremely hard magnetic materials such as FePt have a too large coercive field and cannot be reversed with conventional head fields. The proposed FePt (2 nm)/Fe3Pt (14 nm)/FePt (2 nm) trilayer reduces the coercive field by a factor of 8 compared to a single-phase FePt layer of the same thickness. At the same time the energy barrier is only decreased by 40%. A high signal to noise ratio can be expected for the multilayer structure since the switching field distribution is insensitive on the angle α between the easy axis of the hard layers and the external field. A change from α=0.1° to 1° changes the coercive field by less than 2.5% (10% for conventional perpendicular media). Thus, small distribution of the anisotropy axes angles have less effect than in conventional perpendicular media.

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC05938184

http://dx.doi.org/10.1016/j.jmmm.2004.11.525