Highly oriented permanent magnet and process for producing the same

A process for producing a highly oriented rare earth base permanent magnet which satisfies a dimensional relationship a.gtoreq.b>c, where a is the longer side or major axis of the magnet, b is the shorter side or minor axis of the magnet, and c is the thickness of the magnet, and which has a direction of magnetization inclined at an angle not exceeding 3 degrees with respect to the line normal to the plane defined by a and b, said process comprising the steps of:

• providing a mold comprising magnetic material mold members and nonmagnetic material mold members, said magnetic material mold members and said nonmagnetic material mold members being arranged to form a cavity in said mold, said nonmagnetic material mold members projecting inwardly;
• loading an alloy powder as the starting material into said mold having said cavity that satisfies a relationship A .gtoreq.B>C, where A is the longer side or major axis of the cavity, B is the shorter side or minor axis of the cavity, and C is the depth of the cavity, and said cavity being formed in a substantially uniform parallel magnetic field;
• exerting a compressive force of at least 0.4 tons/cm.sup.2 in a direction substantially perpendicular to the plane defined by A and C while applying a magnetic field in a direction substantially perpendicular to the plane defined by A and B, thereby effecting in-field molding so as to obtain a preform having the direction of magnetization inclined at an angle, said angle being no more than 3 degrees with respect to the line normal to the plane defined by A and B;
• and
• performing cold isostatic pressing at a pressure higher than that employed in the preforming step.