Increase in Nucleation Field of Nanocrystalline Nd(Fe,Co)B Magnets Due to Strengthening of Exchange Interaction-Computer Simulation

The effect of the strength of exchange interaction on the nucleation field H_{N} was studied by computer simulation with varying temperature as well as the size of the non-magnetic phase for Nd(Fe,Co)B magnets composed of fine grains. It was clarified that the spatial distribution of demagnetizing field H_{d} is widened by an increase in the size of the non-magnetic phase and that the ratio of the spatial size of H_{d} to the exchange length L_{\mathrm {ex}} is an important factor of determining H_{N} . Resultantly, the increase in the exchange strength increased H_{N} . Based on this calculation result, magnetic properties of Nd(Fe,Co)B magnets were simulated and it was found that a small amount of substitution of Co for Fe increases L_{\mathrm {ex}} and resultantly improves H_{N} at high temperatures.