Effect of magnetic field strength on the alignment of α′′-Fe16N2 nanoparticle films

Abstract

Aligning the magnetic orientation is one strategy to improve the magnetic performance of magnetic materials. In this study, well-dispersed single-domain core–shell α′′-Fe₁₆N₂/Al₂O₃ nanoparticles (NPs) were aligned by vertically applying magnetic fields with various strengths to a Si wafer substrate followed by fixation with resin. X-ray diffraction indicated that the alignment of the easy c-axis of the α′′-Fe₁₆N₂ crystal and the magnetic orientation of the NPs depended upon the applied magnetic field. Magnetic analysis demonstrated that increasing the magnetic field strength resulted in hysteresis loops approaching a rectangular form, implying a higher magnetic coercivity, remanence, and maximum energy product. The same tendency was also observed when a horizontal magnetic field was applied. The fixation of the easy c-axis alignment of each nanoparticle caused by Brownian rotation under the magnetic field, instead of Néel rotation, was the reason for the enhancement in the magnetic performance. These results on the alignment of the magnetic orientation of α′′-Fe₁₆N₂ NPs suggest the practical application of high-performance permanent bulk magnets from well-dispersed single-domain α′′-Fe₁₆N₂/Al₂O₃ NPs.