Nanostructured magnetic networks: a materials comparison

One method to achieve the enhanced coercivity necessary for the next genera tion of ultra high density recording media is to use a patterned substrate to nanostructure the magnetic material. By sputter-depositing a magnetic fi lm onto the surface of a nanoporous substrate, unique magnetic properties r esult from the reduced dimension and topography of the him, The resultant " network" film has a coercivity nearly two orders of magnitude higher than a continuous thin film of the same thickness. This increase in coercivity ha s been attributed primarily to shape anisotropy due to the proportional rel ationship observed between the coercivity and the moment of the deposited n etwork. To better understand the effect of the shape anisotropy, a number o f different classes of magnetic materials of varying moment and magnetocrys talline anisotropy were deposited onto porous templates and compared. In ge neral, these materials show a peak coercivity in the thickness range of 15- 20 nm. In this thickness the range a linear relationship between the coerci vity and moment is observed confirming the influence of shape anisotropy. A simple model assuming coherent reversal of a magnetized ellipsoid gives a ratio of 1.1 between the short and long axes. This value is significantly s maller than what it is observed by direct imaging. However, if a more reali stic model of magnetization reversal is employed (such as fanning) the rati o obtained is in close agreement with the experiments. (C) 1999 Elsevier Sc ience B.V. All rights reserved.