Correlation between microstructure and magnetic properties of Nd-Fe-Cr-B magnets

Sintered magnets of (Nd/sub 16/Fe/sub 76/B/sub 8/)/sub 1-x/Cr/sub x/ and (Nd/sub 18/Fe/sub 74/B/sub 8/)/sub 1-x/Cr/sub x/ have been prepared by blending Cr powders of different particle sizes with the master magnet powder before sintering. Cr addition is shown to produce changes in the coercive field strength depending on the amount and particle sizes of the Cr powder. The coercivity increase is caused by pinning of domain walls at small inclusions in the intermediate phase and by improved isolation of the hard magnetic grains. Deterioration of coercivity results from a decrease in the intrinsic properties of Nd/sub 2/(Fe, Cr)/sub 14/B phase and nucleation of domain walls at large FeCr inclusion.<
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