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

• Published in: Applied physics letters 2013-12, Vol.103 (24)
• Main Authors: Yang, Meiyin, Allard, Lawrence F., Ji, Nian, Zhang, Xiaowei, Yu, Guang-Hua, Wang, Jian-Ping
• Format: Article
• Language: English
• Subjects: Applied physics; Columnar structure; Domains; Electron diffraction; Image transmission; Iron nitride; Magnetic saturation; Magnetism; Magnetization; Scanning electron microscopy; Scanning transmission electron microscopy; Substrates; Tensile strain; Thin films; Transmission electron microscopy; X-ray diffraction
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4847315

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.