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 <inline-formula> <tex-math notation="LaTeX">$H_{N}$ </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">$H_{d}$ </tex-math></inline-formula> is widened by an increase in the size of the non-magnetic phase and that the ratio of the spatial size of <inline-formula> <tex-math notation="LaTeX">$H_{d}$ </tex-math></inline-formula> to the exchange length <inline-formula> <tex-math notation="LaTeX">$L_{\mathrm {ex}}$ </tex-math></inline-formula> is an important factor of determining <inline-formula> <tex-math notation="LaTeX">$H_{N}$ </tex-math></inline-formula>. Resultantly, the increase in the exchange strength increased <inline-formula> <tex-math notation="LaTeX">$H_{N}$ </tex-math></inline-formula>. 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 <inline-formula> <tex-math notation="LaTeX">$L_{\mathrm {ex}}$ </tex-math></inline-formula> and resultantly improves <inline-formula> <tex-math notation="LaTeX">$H_{N}$ </tex-math></inline-formula> at high temperatures.

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