Rietveld analysis of intensively milled, exchange coupled, nanocrystalline Nd-Fe-B: microstructure and magnetic properties

Rietveld investigations have been applied on intensively milled and annealed stoichiometric Nd2 Fe14 B powders to get detailed information on the microstructure. The obtained data (phase ratio, grain sizes) allow a complete understanding of the magnetic behaviour. Due to an incomplete phase transformation, residual iron dominates the magnetic properties for most samples. Therefore remanent values slightly above 0.8 T cannot clearly be attributed to a size controlled enhancement effect of the 2:14:1 phase. Experiments under optimum inert gas conditions, however, led to nanocrystalline Nd2 Fe14 B powder with residual phases below 2 wt. % and a remanence value of 0.87 T. This result reveals microstructure controlled remanence enhancement on single phase Nd2 Fe14 B prepared by intensive milling, so far only reported for melt spun material. (author)