Our new paper “Grain-size dependent demagnetizing factors in permanent magnets” has been published in Journal of Applied Physics (JAP). http://dx.doi.org/10.1063/1.4904854
UPDATED UPDATE: an updated reprint version that should be better for Google Scholar crawling is now available here
Abstract: The coercive field of permanent magnets decreases with increasing grain size. The grain size dependence of coercivity is explained by a size dependent demagnetizing factor. In Dy free Nd2Fe14B magnets, the size dependent demagnetizing factor ranges from 0.2 for a grain size of 55 nm to 1.22 for a grain size of 8300 nm. The comparison of experimental data with micromagnetic simulations suggests that the grain size dependence of the coercive field in hard magnets is due to the non-uniform magnetostatic field in polyhedral grains.
The article is free to download for 30 days, after which it will be available to journal subscribers. At that time I will post a reprint version on this site, which will be indexed by Google Scholar and other search engines.