Composition-dependent Thin-film Synthesis of Layered Ternary Iron Nitrides FeMN2 (M = W, Mo)

Abstract

Ternary transition-metal nitrides with layered crystal structure host anisotropic bonding and reduced dimensionality that may lead unconventional electronic and magnetic behavior. The synthesis of these layered nitrides phases in thin-film form is difficult because reactive sputtering often favors metastable rocksalt-derived structures. Here we report the composition-dependent thin-film synthesis and characterization of structure and properties of layered ternary iron nitrides FeMN2 (M = W, Mo) with triangular Fe sublattice, prepared by reactive sputtering of amorphous precursors and post-deposition ammonia (NH3) annealing that staggers atomic mixing of the element precursors and long-range crystallization of extended structure. We find that FeWN2 maintains good phase purity across a broad composition range indicative of cation substitution in the layered structure, while FeMoN2 only shows good phase purity in Fe-poor composition, with an optimum corresponding to Fe0.8Mo1.2N2 stoichiometry. Azimuthal grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis shows that in both material systems, Fe-rich films exhibit strong out-of-plane fiber textures, and synchrotron X-ray absorption spectroscopy (XAS) provides insight into local Fe state and environment in both material systems. Room-temperature magnetization measurements of FeWN2 reveal that while the stoichiometric film shows a simple paramagnetic behavior, the Fe-poor films are weakly ferromagnetic. Together, these results suggest that off-stoichiometry and local disorder within the triangular Fe sublattice may partially relieve magnetic frustration in the layered framework, and highlight the strong coupling between composition, microstructure, and magnetic properties in layered nitride materials.