Effects of shape and number of grains on the demagnetization curve calculated for nanocrystalline Nd2Fe14B magnets

Demagnetization curves for nanocrystalline Nd2Fe14B magnets were calculated by using the micromagnetic finite-element technique. The shape of the grains is either cubic or tetrakaidecahedral. If the grain number N of the magnet is small, the calculated curve, especially that for μ0iHc, strongly depends on the applied field direction. The dispersion ranges of μ0iHc along different field directions and the average of these decrease with an increase of N. Upon increasing N to infinity, the average approaches a limit μ0iHc(N=∞). The values for μ0iHc(N=∞) are found to differ slightly for grains of different shapes. When the grain size is small, the values of μ0iHc(N=∞) coincide well with the experimental values for Nd2.33Fe14B1.06Si0.21 magnets with the same grain size with very thin grain boundary phase. Compared with the effects of grain number and the field direction, the effects of the grain shape are small.