Effect of Cr doping on crystallization behavior of Fe3B/Nd2Fe14B nanocomposite permanent magnets

Crystallization behavior and magnetic properties of melt-spun NdxFe82-xB18 and NdxFe79-xCr3B18 (x = 3.5-5.5 at%) alloys have been investigated by means of X-ray diffraction, transmission electron microscopy and magnetization measurements. For both the systems, a similar step proceeds until Fe3B and Nd2Fe23B3 crystallize from the amorphous state. For the Nd5Fe77B18 alloy the metastable compound Nd2Fe23B3 then decomposes along with Fe3B into Fe and nonmagnetic Nd1.1Fe4B4 without any occurrence of hard-magnetic Nd2Fe14B. For the Nd5Fe74Cr3B18 alloy, the decomposition of Nd2Fe23B3 into Nd2Fe14B and Fe3B occurs, resulting in a nanocomposite structure with a large fraction of Nd2Fe14B and a uniform grain size distribution. It is concluded that Cr contributes to increasing coercivity of Fe3B/Nd2Fe14B nanocomposite magnets by inducing the desired scheme of decomposition of the Nd2Fe23B3 compound. (C) 1998 Elsevier Science B.V. All rights reserved.