Nanoscale structure and magnetic properties of Nd-Fe-Nb-B-C permanent magnets

We investigated the nanoscale structure and magnetic properties of Nd/sub 2/(FeNb)/sub 14/(BC)//spl alpha/-Fe. We studied several alloy compositions and the effect of C and Nb on the properties, and thus produced a new alloy of Nd/sub 9/Fe/sub 85.5/Nb/sub 1.0/B/sub 4/C/sub 0.5/. Its mean grain size is about 40 nm. Grain refinement enhanced the remanence, because of greater ferromagnetic exchange coupling between the hard and soft magnetic phase grains. Annealing improved the properties further. By optimizing the processing conditions, we obtained relatively high performance [J/sub r/=1.099 T, H/sub ci/=518.3 kA/m, J/sub r//J/sub s/=0.82, (BH)/sub max/=137.8 kJ/m/sup 3/] when the alloy was annealed at 700/spl deg/C for 15 min. We examined the magnetic domain structure in the nanophase alloy by magnetic force microscopy. The length of the magnetic contrast in the alloy is in the range of 450-550 nm, much bigger than the mean grain size. Here, we interpret the length in terms of interaction domains, which originate from the exchange coupling effect.