A survey of magnetic materials.

Magnetic materials are generally divided into three classes: soft magnetic materials with coercivity H sub c less than about 10 A/cm, hard magnetic materials with H sub c greater than 100 A/cm, and semi-hard magnetic materials with H sub c in between. Soft magnetic materials include low-carbon steel, silicon steel, nickel-iron alloys, cobalt-iron alloys, and spinel ferrites. Hard magnetic materials include Alnicos, hexagonal ferrites, cobalt rare-earths, chromium-cobalt-iron alloys, and more recently, neodymium-rion-boron alloys. Semi- hard magnetic materials include cobalt-iron-vanadidum alloys. Fine particles and continuous films, with coercivities in the range of 250 to 1000 A/cm, are used as magnetic recording media. This paper will provide a general survey, with additional emphasis on current and future trends on magnetic materials development and usage.