Iron-based rare-earth nanocomposite magnet and method for producing the magnet

A method for producing an iron-based rare-earth nanocomposite magnet, the method comprising the steps of:

• preparing a molten alloy having a composition represented by the formula:
• T100−x−y−z−nQxRyTizMn , where T is either Fe alone or Fe in combination with at least one element selected from the group consisting of Co and Ni;
• Q is at least one element selected from the group consisting of B and C;
• R is at least one rare-earth element including substantially no La or Ce;
• and M is at least one metal element selected from the group consisting of Al, Si, V, Cr, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au and Pb, the mole fractions x, y, z and n satisfying the inequalities of
• 5 at %≦x≦8 at %,
• 7 at %≦y≦10 at %,
• 0.1 at %≦z≦5 at % and
• 0 at %≦n≦10 at %, respectively;
• rapidly cooling and solidifying the molten alloy to make a rapidly solidified alloy including at least 20 vol % of R2T14 Q compound phases with an average crystal grain size of 80 nm or less;
• and
• heating the rapidly solidified alloy, thereby making an iron-based rare-earth nanocomposite magnet including the R2T14Q compound phases and α —Fe phases that form a magnetically coupled nanocomposite magnet structure, where the R2T14Q compound phases have an average crystal grain size of 20 nm or more, the α —Fe phases are present at grain boundary triple points in a grain boundary region between the R2T14Q compound phases, the grain boundary region having a thickness of 20 nm or less, wherein a ratio of the average crystal grain size of the R2T14Q compound phases relative to that of the α —Fe phases is 2.0 or more, and the magnet has magnetic properties including a coercivity of at least 400 kA/m and a remanence of at least 0.9 T.