SHEET MAGNET HAVING MICROCRYSTALLINE STRUCTURE AND METHOD OF MANUFACTURING THE SAME, AND METHOD OF MANUFACTURING ISOTROPIC PERMANENT MAGNET POWDER

摘要

PURPOSE: A thin-film magnet optimal for use in various types of small motors, actuators, and magnetic circuits for magnetic sensors and a method for its manufacture is provided. CONSTITUTION: A sheet magnet having a residual magnetic flux density Br of not less than 10kG, a cost performance equal to that of a hard ferrite magnet, and a thickness of 70 SIMILAR 300 mu m contributing to the miniaturization and thinning of a magnetic circuit, and a method of manufacturing the same. When a molten alloy of a predetermined structure having a small content of a rare earth element is subjected to continuous casting using a cooling roll in a vacuum inert gas atmosphere of not more than 30 kPa at a predetermined peripheral speed of the roll, it turns into a crystalline structure substantially not less than 90 % of which comprises a FE3B type compound and a compound phase having alpha -Fe and Nd2Fe14B type crystalline structures compatible with the former. A continuous sheet magnet of 70 SIMILAR 300 mu m in thickness comprising a microcrystalline structure of 10 SIMILAR 50 nm in average crystal grain diameter having magnetic characteristics of iHc >/= 2kOe, Br >/= 10kG and practically usable as a permanent magnet can be obtained. A sheet magnet which has heretofore been difficult to be industrially produced can be mass-produced at a low price by a simple method.