Effect of particle size on the magnetization process in lithographic arrays of Nd₂Fe₁₄B

Controlled arrays of Nd₂Fe₁₄B were fabricated via sputtering and lithography. The arrays were fabricated via optical and electron-beam lithography combined with dry etching technique. Designed particle size varies from 10 μmX10 μm to 0.5 μmX0.5 μm. We found an increase in the coercive field with decreasing particle size. Results of the micromagnetic calculations suggest that the coercive-field increase in smaller-sized particles is originated from the effective decrease in the exchange-coupling energy owing to the relative increase in the fraction of surface grain.