The effects of refractory metals on the magnetic properties of /spl alpha/-Fe/R/sub 2/Fe/sub 14/B-type nanocomposites

摘要

The phase transformations and magnetic properties of rare earth lean and boron rich (Nd/sub 0.95/La/sub 0.05/)/sub x/Fe/sub bal./M/sub 2/B/sub 10.5/, where x=9.5 or 11 and M=Cr, Ti, Nb, V, Mo, Zr, Nf, Ta, Mn or W, melt spun ribbons have been investigated. Two magnetic phases, namely /spl alpha/-Fe and R/sub 2/Fe/sub 14/B, were found in ribbons studied. A third magnetic phase, the R/sub 2/Fe/sub 23/B/sub 3/, was also detected in (Nd/sub 0.95/La/sub 0.05/)/sub 9.5/Fe/sub 78/M/sub 2/B/sub 10.5/ (M=Mo and Mn). Remanence (B/sub r/) and coercivity (/sub i/H/sub c/) values in the range of 8.0 to 9.1 kG and 9.5 to 18.9 kOe, respectively, have been achieved in nanocomposites with merely two magnetic phases. Among compositions studied, the Ti and W-substitutions were found to be most effective in increasing the B/sub r/ and /sub i/H/sub c/, respectively. For a fixed refractory metal substitution, namely, M=Cr, Ti or Nb, an increase in the total rare earth concentration resulted in nanocomposites of small grain sizes and a high volume fraction of the R/sub 2/Fe/sub 14/B phase. The combination of fine grain size and high volume fraction of R/sub 2/Fe/sub 14/B phase led to an increase in the /sub i/H/sub c/ and maximum energy product, (BH)/sub max/ of nanocomposites studied. A B/sub r/ of 9.1 kG, /sub i/H/sub c/ of 16.7 kOe and (BH)/sub max/ of 16.8 MGOe have been obtained on (Nd/sub 0.95/La/sub 0.05/)/sub 11/Fe/sub 76.5/Ti/sub 2/B/sub 10.5/.