  Epitaxial Fe4N thin films grown on lattice-matched LaAlO3 (LAO) substrate
using sputtering and molecular beam epitaxy techniques have been studied in
this work. Within the sputtering process, films were grown with conventional
direct current magnetron sputtering (dcMS) and for the first time, using a high
power impulse magnetron sputtering (HiPIMS) process. Surface morphology and
depth profile reveal that HiPIMS deposited film has the lowest roughness, the
highest packing density and the sharpest interface. La from the LAO substrate
and Fe from the film interdiffuse and forms an undesired interface spreading to
an extent of about 10-20 nm. In the HiPIMS process, layer by layer type growth
leads to a globular microstructure which restricts the extent of the
interdiffused interface. Such substrate-film interactions and microstructure
play a vital role in affecting the electronic hybridization and magnetic
properties of Fe4N films. The magnetic moment (Ms) was compared using bulk,
element-specific and magnetic depth profiling techniques. We found that Ms was
the highest when the thickness of the interdiffused layer was lowest and only
be achieved in the HiPIMS grown samples. Presence of small moment at the N site
was also evidenced by element-specific x-ray circular dichroism measurement in
HiPIMS grown sample. A large variation in the Ms values of Fe4N found in the
experimental works carried out so far could be due to such interdiffused layer
which is generally not expected to form in otherwise stable oxide substrate. In
addition, a consequence of substrate-film interdiffusion and microstructure
results in different kinds of different kind of magnetic anisotropies in films
grown using different techniques.
