Structural and magnetic properties of Co-N thin films deposited using magnetron sputtering at 523 K

Abstract

In this work, we studied cobalt nitride (Co-N) thin films deposited using a dc magnetron sputtering method at a substrate temperature (Ts) of 523 K. We find that independent of the reactive gas flow (RN2) used during sputtering, the phases of Co-N formed at this temperature seems to be identical having N at.% ∼ 5. This is contrary to Co-N phases formed at lower Ts. For example at Ts∼ 300 K, an evolution of Co-N phases starting from Co(N) → Co4N → Co3 N → CoN can be seen as RN2 increases gradually to 100%, whereas when Ts increases to 523 K, the phase formed is fcc Co along with a minuscule Co4N phase for RN2 ≥ 25%. We used x-ray diffraction (XRD) to probe long range ordering, x-ray absorption spectroscopy (XAS) at Co absorption edge for the local structure, Magneto-optical Kerr effect (MOKE) and polarized neutron reflectivity (PNR) to measure the magnetization of samples. Quantification of N at.% was done using secondary ion mass spectroscopy (SIMS). Measurements suggest that the magnetic moment of Co-N samples deposited at 523 K is slightly higher than the bulk Co moment and does not get affected with the RN2 used for reactive sputtering. Our results provide an important insight about the phase formation of Co-N thin films which is discussed in this work.