  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.
