R-Fe-B system fine crystal density magnet

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According to the present invention, an R-Fe-B based rare-earth alloy powder with a mean particle size of less than 20 µm is provided and compacted to make a powder compact. Next, the powder compact is subjected to a heat treatment at a temperature of 550 °C to less than 1, 000 °C within hydrogen gas, thereby producing hydrogenation and disproportionation reactions (HD processes). Then, the powder compact is subjected to another heat treatment at a temperature of 550 °C to less than 1, 000 °C within either a vacuum or an inert atmosphere, thereby producing desorption and recombination reactions and obtaining a porous material including fine crystal grains, of which the density is 60% to 90% of their true density and which have an average crystal grain size of 0.01 µm to 2 µm (DR processes). Thereafter, the porous material is subjected to yet another heat treatment at a temperature of 750 °C to less than 1, 000 °C within either the vacuum or the inert atmosphere, thereby further increasing its density to 93% or more of their true density and making an R-Fe-B based microcrystalline high-density magnet.