PURPOSE: To convert a surface layer into amorphous state and to form a firm highly corrosion resistant protective layer by irradiating the surface of a rare earth-iron magnetic material with a high energy electron beam.

CONSTITUTION: The surface of a polycrystal as rare earth-iron magnetic material is irradiated with a high energy electron beam having ≥10keV pressure voltage to undergo rapid heating and is then cooled rapidly, by which the surface layer is structurally converted into highly corrosion resistant amorphous state. The amount of iron oxide (Fe2O3) is reduced with the increase in the thickness of the amorphous layer, and corrosion resistance can be improved. Accordingly, the chances of application of this magnet to purposes requiring resistance to severe environment can be improved.