THIN FILMS FOR MAGNETIC RECORDING

Thin films of the ferromagnetic metals have been shown in the last few years to possess recording characteristics far superior to those of the more conventional, thicker particulate On the basis of simple physical principles, it was anticipated that media of high coercivity and media that were thin yet possessed sufficient magnetic moment for sensing would tend to yield higher resolution in magnetic recording. These anticipations have not only been realized, but the ability to vary the magnetic properties of thin films over large ranges has led to the experimental verification of the dependence of recording behavior on the nature of the medium, i.e., its thickness and magnetic properties. As has been discussed in previous p a p e ~ s , ~ the output has been shown to be some f(H,. . M,.) while the resolution is a f(H,/t) . The recording behavior has been covered previously in some detail. The purpose of this paper, therefore, will be to review how these thin films are fabricated and how their magnetic properties and perhaps other properties are related to their recording behavior. Films suitable for magnetic recording generally lie in the thickness range from 500 angstroms to several microns and are magnetically hard, generally metallic (i.e., H, is greater than 150 oersteds). These films can be fabricated (or at least the attempt has been made to fabricate them) in practically all the ways that thin films for any application are fabricated. The most successful means, however, have involved electrodeposition, electroless deposition, vacuum deposition, and sputtering. Although the properties of these films arise from their composition and structures and therefore may be theoretically independent of their method of fabrication, in practice, certain methods of fabrication easily produce certain structures and compositions that cannot be reproduced easily by other means. As a consequence, it is both convenient and meaningful to discuss these films in relation to their means of fabrication.