Unusually high coercivity of sputtered Fe16N2 thin films on MgO (001) substrate

Abstract

alpha ''-Fe16N2 is a highly promising material for advanced permanent magnet applications due to its exceptional magnetic properties, including ultrahigh saturation magnetization and relatively high magnetocrystalline anisotropy. In this study, alpha ''-Fe16N2 thin films were epitaxially fabricated on MgO (001) single-crystal substrates using Fe (001) seed layers with a facing target sputtering system. Only (00L) reflections of alpha ''-Fe16N2 were observed, indicating that the films are well-textured. The degree of nitrogen ordering in the alpha ''-Fe16N2 phase (with the N-disordered phase being alpha'-Fe8N) reached 0.44. The saturation field (Hs) increased to similar to 7200 Oe with increasing film thickness. Stripe magnetic domain strucures were observed by Magnetic Force Microscopy (MFM), suggesting the formation of out-of-plane oriented magnetic domains. It was found that at critical thickness, an unusually high coercivity value of 884 Oe was achieved for those continuous films. MFM images revealed that the decrease in domain size at this thickness corresponded to an increase in coercivity, reaching its maximum value. This high coercivity observed indicates that the Fe16N2 films exhibit hard magnetic properties, making them a promising candidate for some thin film permanent magnet application, e.g., magnetic microelectromechanical systems (MEMS).