XMCD and TEM studies of as-cast and rapidly quenched Fe_(50)Nd_(50) alloys

摘要

We present the XMCD analysis of as-cast and melt spun Fe_(50)Nd_(50) samples performed at L_(2,3)-Nd and K-Fe absorption edges at 5 and 50 K in comparison with macroscopic data of XRD, TEM and magnetic properties measurements. In addition, we have measured the magnetic field dependence of XMCD signal for both types of the samples in magnetic fields up/down to 17 T. The obtained results pointed to the strong difference between structure and magnetic properties of the as-cast and melt spun Fe_(50)Nd_(50) alloys for both macroscopic and local measurements. The element selective XMCD loops for melt spun alloy show almost identical value of the coercive force H_(ci) for L_2-Nd and K-Fe edges and practically do not depend on temperature. XMCD loop at K-Fe edge is a sum of contributions of the Fe-based phases. The main Fe-rich phase has high H_(ci) ≈ 2,4 T as a highly anisotropic phase. The absence of the K-Fe XMCD loop saturation in the field up to 17 T points to presence of the second Nd-rich Nd-Fe phase which is ferromagnetic at temperature lower than 50 K. In accordance to the TEM results these both phases may coexist as the mixture of nanocrystals which was formed as a result of decomposition of the amorphous-like matrix phase. The XMCD loop at L_2-Nd edge with H_(ci) ≈ 1,9 T is the sum of contributions from two Nd-based phases: hard Fe-rich phase (H_(ci) ≈ 2,4 T) and Nd-Fe matrix phase of medium hardness with H_(ci) ≈ 1,3 T. The macroscopic loop showed the higher H_(ci) compared to XMCD loops. Such discrepancy may be caused by the fact that XMCD signal is collected from a 5-10 mcm thick surface layer, which contains many defects that reduce anisotropy and coercivity.