The effect of strain induced by Ag underlayer on saturation magnetization of partially ordered Fe16N2 thin films

Abstract

Partially ordered Fe-N thin films were grown by a facing target sputtering process on the surface of a (001) Ag underlayer on MgO substrates. It was confirmed by x-ray diffraction that the Ag layer enlarged the in-plane lattice of the Fe-N thin films. Domains of the ordered α″-Fe16N2 phase within an epitaxial (001) α′-FexN phase were identified by electron diffraction and high-resolution aberration-corrected scanning transmission electron microscopy (STEM) methods. STEM dark-field and bright-field images showed the fully ordered structure of the α″-Fe16N2 at the atomic column level. High saturation magnetization(Ms) of 1890 emu/cc was obtained for α″-Fe16N2 on the Ag underlayer, while only 1500 emu/cc was measured for Fe-N on the Fe underlayer. The results are likely due to a tensile strain induced in the α″-Fe16N2 phase by the Ag structure at the interface.