Sm2Fe17 interstitial magnets (invited)

Various processing routes for making permanent magnets based on interstitially modified Sm2Fe17 have been recently developed. Zn bonding of coarse grained Sm2Fe17N3 gives coercivities μ0JHc as high as 2.2 T. Effective methods to prepare highly coercive Sm2Fe17N3 powders for polymer bonding are mechanical alloying and rapid quenching. With the very simple method of additional milling of coarse grained nitrided powders we achieved μ0JHc≊1.5 T. A coercivity up to 3.5 T has been achieved by a modified HDDR procedure, reducing the particle size of the starting material by milling prior to the hydrogenation–disproportionation–desorption–recombination (HDDR) treatment. This is attributed to a better control of two critical parameters, namely grain size and the amount of unrecombined α-Fe accompanying the intermediate TbCu7 structure-type phase. Resin bonded HDDR-Sm2Fe17N3 magnets show an unexpected high initial susceptibility. This may be due to a strong magnetic interaction of the grains. To develop coercivity in Sm2Fe17Cy≳1 obtained by gas–solid reactions of Sm2Fe17 the same methods as those applied to Sm2Fe17N3 can be successfully used. Fully dense magnets with a coercivity up to 1.5 T were made from the interstitially as well as substitutionally modified compound Sm2Fe15Ga2C2 by hot pressing of highly coercive powders.