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 (Nd_0.95La_0.05)_xFe _bal.M₂B_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 α-Fe and R₂Fe ₁₄B, were found in ribbons studied. A third magnetic phase, the R₂Fe₂₃B₃, was also detected in (Nd _0.95La_0.05)_9.5Fe₇₈M₂ B_10.5 (M=Mo and Mn). Remanence (B_r) and coercivity (_iH_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 _iH_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 ₂Fe₁₄B phase. The combination of fine grain size and high volume fraction of R₂Fe₁₄B phase led to an increase in the _iH_c and maximum energy product, (BH)_max of nanocomposites studied. A B_r of 9.1 kG, _iH_c of 16.7 kOe and (BH)_max of 16.8 MGOe have been obtained on (Nd_0.95La_0.05)₁₁ Fe_76.5Ti₂B_10.5