MAGNETIC MATERIAL FOR THERMOMAGNETIC RECORDING MEDIUM AND ITS PRODUCTION

摘要

PURPOSE:To set the Curie point temp. based on the combination ratio between iron and nitrogen within a practicable temp. range by subjecting pulverous iron powder to reduction nitridation for a prescribed period at a prescribed temp. in an atm. of a gaseous mixture composed of NH3 and H2 and setting the combination ratio of the iron and nitrogen in such a mannr as to form epsilon-phase iron nitride Fe3N-Fe2.2N. CONSTITUTION:The desired product is obtd. by bringing the pulverous iron powder into reaction with the gaseous mixture composed of ammonia/hydrogen for the prescribed period at the prescribed temp. The raw material which can be used includes high-purity iron oxide, iron oxyhydroxide and iron oxalate. The raw material is preferably subjected to a treatment for preventing sintering using phosphoric acid, etc. as a pretreatment in order to prevent the sintering among the particles. The material treated by an alkali method rather than an acid method has the easier tendency to progression of nitridation reaction and better magnetic characteristics in the case of using goethite and hematite. The reaction temp. is preferably in an about 350-550 deg.C range in general, although the optimum temp. thereof varies slightly with raw materials.