Ferromagnetic coercivity of Sm-Co alloys

We have investigated the Sm2(Co,Fe,Cu,Zr,Cr)14.8permanent magnets by NMR using both the Co and Sm nuclei and by Mossbauer spectroscopy using the Fe nucleus. A full set of samples was prepared, each containing an additional constituent regarding its predecessor. Samples were analysed, both prior to and after step annealing designed to precipitate out a uniform 2nd phase structure. Our findings are: 1) the addition of Cu precipitates out Fe and Co; noting the shift in the hyperfine field concurrent with this precipitation, one can assume the replacement of these transition metals by the Cu; 2) the addition of Fe causes some substitutional displacement for the Co with the remainder being Undissolved in ar Fe-Co phase-this increases the remanence; 3) further removal of free Fe is accomplished through the addition of Zr and a subsequent step anneal; thus Zr helps increase the remanence by dissolving Fe; 4) the second, and more important, role of the Zr is known to be an increase in the coercive force, our results indicating that Zr preferentially substitutes in the 1:5 phase-problably replacing the Sm-lowering the magnetic properties of the cellular boundary 1:5 phase, causing it to exert a more effective pinning of the domain walls, in agreement with experimental findings; 5) the addition of Cr with Zr causes the preferential substitution of Fe into the 4f site of the 2:17 phase, thereby increasing the anisotropy and facilitating the removal of the Fe-Co phase. This represents one of the first times that the functions of the constituents of a complex intermetallic alloy has been able to be analysed on a microscopic basis by resonance techniques.