Recent developments in magnetic recording materials (invited)

Abstract

Modern recording surfaces call for small, uniform, highly dispersible and orientable particles with high coercivity and an appropriate moment density or, alternatively, thin films having similar properties. Greatly improved particles of all kinds have been introduced in the last few years. The list includes iron oxides with compositions in the range Fe₂O₃–Fe₃O₄ (H_c = 250–450 Oe), cobalt‐modified iron oxides and chromium dioxide (H_c = 450–700 Oe), and particles of iron, cobalt and their alloys (H_c = 700–1100 Oe). Increasing coercivity corresponds at present to lesser commercial importance and unfortunately, the more attractive magnetic properties seem almost invariably to be associated with thermal, mechanical or chemical instability. Metallic films continue to be attractive because of their thinness, magnetic material undiluted by non‐magnetic material, flexibility of magnetic properties and low noise, but their disadvantages include poor reproducibility, poor resistance to wear and propensity to high levels of defects and to corrode. Recent developments of each kind of recording material will be reviewed with particular emphasis being given to unsolved problems.