Prediction of improved magnetization and stability in Fe16N2 through alloying

Abstract

We study the structural, energetic, electronic, and magnetic properties of Fe16 − xMxN2 alloys, where M represents 3d transition metals Ti, V, Cr, Mn, Co, and Ni, using special quasirandom structures and density functional theory calculations. We describe stabilization of Fe16N2 resulting from the enhanced occupation of bonding states relative to the corresponding antibonding states as observed from crystal orbital Hamiltonian population analysis. The hybrid HSE06 functional is employed to calculate a magnetic moment of 2.844 μB/Fe, agreeing with recent experimental work and suggesting the importance of electronic exchange effects. Upon alloying, magnetization is found to decrease with all transition metals excluding Mn, for which exceptionally strong ferromagnetic coupling is achieved via nitrogen-mediated exchange interactions. We identify a 1.41% magnetization increase at low Mn concentrations coupled with a decrease in formation energy, making Fe16 − xMnxN2 a suitable candidate for permanent magnet applications. Novel end-member systems of the form M16N2 are also investigated, with results implying stability and potential synthesizability of all compounds except Ti16N2 owing to weak metallic bonding among Ti atoms.