Phase formation, thermal stability and magnetic moment of cobalt nitride thin films

TL;DR

This study investigates the phase formation, thermal stability, and magnetic properties of cobalt nitride thin films prepared via reactive magnetron sputtering, revealing phase-dependent lattice expansion and enhanced magnetic moments surpassing pure cobalt.

Contribution

It provides new experimental evidence of magnetic moments exceeding pure cobalt in cobalt nitride films and explains this via a large-volume high-moment model.

Findings

Formation of multiple Co-N phases with increasing nitrogen flow.

Lattice expansion correlates with nitrogen content and phase.

Magnetic moments surpass pure Co due to lattice expansion and high-moment effects.

Abstract

Cobalt nitride (Co-N) thin films prepared using a reactive magnetron sputtering process by varying the relative nitrogen gas flow (\pn) are studied in this work. As \pn~increases, Co(N), \tcn, Co$_3$N and CoN phases are formed. An incremental increase in \pn, after emergence of \tcn~phase at \pn=10\p, results in a continuous expansion in the lattice constant ($a$) of \tcn. For \pn=30\p, $a$ maximizes and becomes comparable to its theoretical value. An expansion in $a$ of \tcn, results in an enhancement of magnetic moment, to the extent that it becomes even larger than pure Co. Though such higher (than pure metal) magnetic moment for Fe$_4$N thin films have been theoretically predicted and evidenced experimentally, higher (than pure Co) magnetic moment are evidenced in this work and explained in terms of large-volume high-moment model for tetra metal nitrides.