Isotropic permanet magnet formed of a sintered body having a mean crystal grain size of 1-130 microns and a major phase of tetragonal system comprising, in atomic percent, 10-25% of R wherein R represents at least one of rare-earth elements including Y, 3-23% of B, no more than 50% of Co and the balance being Fe. As additional elements M, Al, Ti, V, Cr, Mn, Zr, Hf, Nb, Ta, Mo, Ge, Sb, Sn, Bi, Ni or W may be incorporated.The magnets can be produced through a powder meallurgical process resulting in high magnetic properties, e.g., up to 7 MGOe or higher energy product.