  This work demonstrates synthesis and study of fcc-Co derived from an
isostructural Co4N. Diffusion measurements carried out in this work, reveal
that N self-diffusion is the swiftest in Co4N compared to other transition
metal nitrides or even the mononitride CoN. By the application of a high
substrate temperature (Ts) growth or thermal annealing temperature (Ta); N
diffuses out from the fcc-Co4N above 573 K leaving behind a high purity fcc-Co
phase. Generally, Co grows in a hcp structure and a (partial) hcp to fcc-Co
transformation takes place around 700 K or above 70 GPa. The proposed route
through nitridation and diffusion of N not only bring down the phase transition
temperature, an impurity present in the form of hcp-Co can be avoided
altogether. Oriented Co4N(111) thin films were grown using a CrN(111) template
on a quartz substrate using a dc magnetron sputtering. Samples were grown at
different Ts or room temperature grown Co4N samples were annealed at different
Ta. Analysis using x-ray diffraction, N K-edge x-ray absorption, x-ray
photoelectron and secondary ion mass spectroscopy confirmed the formation of
fcc-Co4N or fcc-Co phases. It was found that Co-N bonding and N concentration
get significantly reduced at a high Ts or Ta. Magnetization measurements
combining ex-situ and in-situ magneto-optical Kerr effect showed differences in
anisotropy and coercivity of Co4N and fcc-Co samples. Combining structural,
electronic and magnetization measurements, it has been observed that a high
purity fcc-Co can be conveniently derived from the isostructural Co4N aided by
an exceptionally high N self-diffusion in Co4N.
