PURPOSE: To contrive to increase coercive force by a method wherein a molded alloy comprising Co, Fe, an rare earth element, a specific transition metal in a specific ratio is sintered and, after magnetized, ageing treatment is applied thereto to prevent 4πJs deterioration during ageing treatment.

CONSTITUTION: An alloy having a composition shown by a general formula R(Co1-x-yFexMy)z is prepared. In said formula, R is one or more of Y, Ce, Nd, Pn, Sm, Gd, Dy and a misch metal, M is one or more of Ti, Cr, V, Mn, Ni, Cu, Zn, Zr, Nb, Hf, Ta and W, x, y, z are respectively 0.02≤x≤0.5, 0.01≤y≤0.3, 8≤z≤9. Said alloy is finely divided and subjected to compression molding and, after resultant molded body is sintered or subjected to preliminary ageing treatment at about 750W850°C for about 0.1W10hr after sentering, the resultant sintered body is magnetized and ageing treatment is applied thereto at a temp. of about 800°C or less capable of holding a magnetized condition.