Effect of magnetocrystalline anisotropy on the magnetic properties of Fe-rich R-Fe-B nanocomposite magnets

Nanocomposite ribbons consisting of hard-magnetic R2Fe14B (R = rare-earth) and soft-magnetic Fe3B phases were produced by melt spinning and subsequent heat treatment. Alloys of composition Nd4-xSmxFe77.5B18.5, with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 all showing strong remanence enhancement, were selected to investigate the effect of the magnetocrystalline anisotropy of the R2Fe14B-type phase on the exchange coupling with the soft-magnetic phase in the nanocomposite magnets. An enhancement of exchange coupling due to anisotropy reduction was found, as expected on the basis of the model of Kneller and Hawig. A maximum of the energy product (BH)(max) was achieved for x = 0.2 after annealing at 700 degrees C. The thermomagnetic behavior also changes upon substitution of Sm for Nd. (C) 1999 American Institute of Physics. [S0003-6951(99)01841-0].