Abstract
The intrinsic coercive force of compacts prepared from hydrogen-reduced ferric oxide powder has been studied as a function of particle size in the range 200–800 Å. For well-dispersed powder the coercive force increases sharply with particle size to a value of 970 oersteds, where the nominal particle size is 260 Å.; above this value the coercive force decreases sharply. An electron-microscope study of powders in the neighbourhood of the maximum shows that the experimentally determined coercive force is in good agreement with recent theory. X-ray line-broadening experiments indicate that packing effects, rather than strain anisotropy within particles, control the coercive force of compacts. A linear variation with packing density is obtained for all particle sizes investigated.
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