Biomedical Engineering Reference
In-Depth Information
photoelectron spectroscopy (XPS). The magnetic properties of samples have
been characterized employing vibrating sample magnetometer (VSM) and
ferromagnetic resonance (FMR) techniques.
Nanocrystalline Fe-Ni thin films have been prepared by the partial
crystallization of vapor-deposited amorphous precursors. The microstruc-
ture was controlled by annealing the films at different temperatures. X-ray
diffraction, transmission electron microscopy and energy dispersive x-ray
spectroscopy investigations showed that the nanocrystalline phase was that
of Fe-Ni. Grain growth was observed with an increase in annealing
temperature. X-ray photoelectron spectroscopy observations showed the
presence of native oxide layer on the surface of the films. Magnetic studies
using a vibrating sample magnetometer showed that coercivity has a strong
dependence on grain size. This is attributed to the random magnetic
anisotropy characteristics of the system. The observed coercivity depen-
dence on grain size is explained using modified random anisotropy model.
Glancing angle x-ray diffraction studies showed that the irradiated films
retain their amorphous nature. The topographical evolution of the films
under swift heavy ion bombardment was probed using atomic force
microscopy and it was noticed that surface roughening was taking place
with ion beam irradiation. Magnetic measurements using a vibrating sample
magnetometer showed that the coercivity of the films increased with an
increase in ion fluence. The observed coercivity changes are correlated with
topographical evolution of the films under swift heavy ion irradiation.
Investigations on the effect of thermal annealing on the surface roughness
of the Fe-Ni thin found that surface smoothing of the film occurs at higher
annealing temperature. Ferromagnetic resonance measurements revealed
that the demagnetizing field along the in-plane direction decreased with
annealing temperature while that along the out-of plane direction increased.
This resulted in a transition of surface magnetization direction from out-of-
plane to in-plane. The observed modifications of the magnetic properties are
correlated with annealing induced surface modification in Fe-Ni thin films.
Atomic force microscopy was used to study the evolution of the surface of
these columnar thin films with deposition time. It has been found that the
root mean square roughness increased with deposition time but showed a
less significant change at longer deposition times. The separation between
the nanostructures increased sharply during the initial stages of growth and
the change was less significant at higher deposition time. These results
suggest that, during initial stages of growth, self-shadowing dominates and
as deposition time increases surface diffusion also plays an active role in the
growth process.
It is important to note the influence of substrate surface roughness on the
structural and magnetic properties of obliquely deposited amorphous
nanocolumns of Fe-Ni. Experiments showed that the surface roughness
