The effects of grain condition on magnetic properties in Nd4Fe76Co3(Hf1-xGax)B-16 alloy

The best linear fit of H-c(T)/M-s(T) versus 2k(1)(T)/mu(0)M(s)(2)(T) implie s that H-c is determined by a nucleation process in nanocrystalline two-pha se magnets. The condition of the grain shapes is improved after adding Hf a nd Ga, but the surfaces are deteriorated by some precipitates on the bounda ry. Taking into account the values of alpha, N-eff, the results of transmis sion electron microscopy (TEM), and Mossbauer spectroscopy, the magnetic fi eld heat treatment not only induces grain refinement but also causes a unif orm distribution of the soft and hard phases. Both the remanence and energy product values are increased by 20-30% for all ribbons after annealing wit h magnetic field. The magnetic interaction in Nd2Fe14B/Fe3B + alpha Fe-base d nanocrystalline two-phase magnets is studied using delta M plots in this paper. It is found that the exchange-coupled interaction is greatly enhance d in the sample annealed with magnetic heat treatment, especially Nd4Fe76Co 3Hf0.5Ga0.5B16, which achieves the highest energy product (BH)(max) = 15.8 MGOe.