The effects of refractory metals on the magnetic properties of α-Fe/R2Fe14B-type nanocomposites

The phase transformations and magnetic properties of rare earth lean and boron rich (Nd0.95La0.05)(x)Febal.M2B10.5 where x = 9.5 or 11 and M = Cr, Ti, Nb, V, Mo, Zr, Hf, Ta, Mn or W, melt spun ribbons have been investigated. Two magnetic phases, namely alpha-Fe and R2Fe14B, were found in ribbons studied. A third magnetic phase, the R2Fe23B3, was also detected in (Nd0.95La0.05)(9.5)Fe78M2B10.5 (M = Mo and Mn). Remanence (B-r) and coercivity (H-i(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-r and H-i(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 R2Fe14B phase. The combination of fine grain size and high volume fraction of R2Fe14B phase led to an increase in the H-i(c) and maximum energy product, (BH)(max) of nanocomposites studied. A B-r of 9.1 kG, H-i(c) of 16.7 kOe and (BH)(max) of 16.8 MGOe have been obtained on (Nd0.95La0.05)(11)Fe76.5Ti2B10.5.