Indian Journal of Engineering & Materials Sciences
Vol. 11, August 2004, pp. 353-357
Preparation and characterization of vacuum deposited magnetic
polyaniline thin films†
Prafull Mathura, S C K Misraa, Ram Kishoreb, U C Upretib & J L Pandeya
a
Engineering Materials Division, bMaterials Characterization Division
National Physical Laboratory, New Delhi 110 012, India
Received 24 January 2003; accepted 20 October 2003
Vacuum deposited polyaniline thin films have been found to exhibit excellent magneto-optic properties. The vacuum
deposited thin films of doped polyaniline have been prepared on various substrates and their optical, electrical and magnetic
characterization carried out. The thin films prepared on different substrate show a variety of surface topography and
magnetic domains in crystalline phase. The crystallinity is induced by the influence of substrate on which the film is
deposited. This technology establishes the feasibility of preparation of high-density disc storage magnetic recording media
using vacuum deposited thin films. The advantage of these films is their magnetization at lower magnetic fields.
IPC Code: Int. Cl.7 H01F 10/26
During the last few decades there is remarkable
growth of interest in development of magnetic thin
films for industrial and technological applications
particularly
as
recording
media.
The
microminiaturization has led to the development of
computer
equipment,
surgical
tools
and
communications pipelines shrink ever smaller, the
next step in engineering is to merge biological and
mechanical molecules and compounds into really,
small machines. This may happen in many different
ways like collection of information by fastest methods
and efficient and compact storing of the information
in smallest space. This can be done by miniaturizing
the magnetic storage devices. Such devices can be
prepared by using nano-technology using dimensions
and tolerances in the range of 0.1-100 nm. This also
accelerates the need of miniaturization of magnetoopto-electronic devices. This is made possible by
using nano-crystalline polymeric thin films magnetic
devices. The magnetic polymeric thin films have
several advantages over conventional inorganic ones
like ease of fabrication, low temperature processing
and a very flexible metrology for preparation of film
with desired properties. These films are used for
magnetic gyrator for phase shifters, insulators and
amplifiers, magnetic memory devices disc storage,
_______________
Presented at International Workshop on Recent Advances in
Nanotechnology of Magnetic Fluids, held at National Physical
Laboratory, New Delhi, during 22-24 January 2003.
magnetic tapes and sheets and cards. It is therefore,
essential to study the magnetic properties and the
details of feasibility of preparation of nano-crystalline
magnetic polyaniline thin films. There have been
studies on determination of magnetic susceptibility
and polyaniline and its blends as in the past few years
as the polymeric magnetic materials have become
increasingly important in the area of information
storage and magnetic recording1-8. The thin film
magnetic configuration depends on various
experimental factors like deposition, size, shape,
structure, substrate, processing, contamination and so
on. Magnetic metal doped polyaniline is emerging as
a new materials for preparation of magnetic thin film
for recording media. Vacuum deposited thin films are
the best and preferred media for use as magnetic
films. The magnetic polyaniline structure remains
unchanged after vacuum evaporation due to
polymerization and conjugation of the chains broken
during the evaporation9-11. It has been established that
polyaniline has a magnetic behaviour arising from its
electronic and lattice contributions and gives rise to
reasonable magnetic susceptibility, which varies with
temperature. Polyaniline possesses diamagnetic
susceptibility indicating the existence of free electron
spins. Adding various dopants so as to enhance the
magnetization of polyaniline further can modify the
density of states of free electrons. This magnetic
polyaniline has a potential of being used as active
magnetic device in the form of powder, pellets or thin
354
INDIAN J ENG. MATER. SCI., AUGUST 2004
films. The films can be prepared by various methods
for many applications. We have devised a completely
dry process to prepare polyaniline thin films by
vacuum evaporation of polyaniline powder onto
suitable substrate. These films can be made magnetic
by suitably doping the polyaniline powder during the
synthesis. The preparation and study of magnetic
polyaniline vacuum deposited thin films for use in
magnetic data storage applications has been reported.
Experimental Procedure
Preparation of un-doped and Fe-doped polyaniline
nano-crystalline films was done in two steps. First,
preparation of polymer and preparation of polymeric
magnetic film on a substrate and second, preparation of
nano-crystalline polymeric thin films on suitable
substrates. A copolymer of aniline and formaldehyde
was prepared by dissolving 10.5 g of aniline in 12.5
mL of 10 M hydrochloric acid diluted with 11 mL
distilled water. 12 mL of 25% formaldehyde solution
was added to this solution, followed by addition of
ferric chloride in a predetermined quality. The resultant
solution was stirred for 60 min and poured into 200 mL
of 5-10% NaOH solution. The precipitate obtained was
filtered, washed and dried. This powder was used for
preparation of polymeric films by evaporation on glass
substrate under a vacuum of 10-6 mm Hg. The accurate
temperature for evaporation of polyaniline powder was
determined by carrying out DTA of Fe-doped
polyaniline powder so as to ensure a perfect
homogeneous Fe-doped uniform polyaniline thin film
and also to determine the polyaniline evaporation
temperature (Fig. 1). The optical characterization of
vacuum deposited magnetic polyaniline thin films was
carried out using Hitachi UV-3400 spectrophotometer,
Mössbauer spectro-scopy, surface topography, X-ray
diffraction analysis, electron spin resonance and
Fig. 1⎯DTA (differential thermal analysis) of magnetic Fe-doped
polyaniline
electrically detected magnetic resonance were carried
out. Since the thickness of the vacuum deposited films
is of the order 1000Å, it was required to carry out
measurements at low fields.
To study the magnetic properties of a material it is
essential to magnetize the polymeric thin film
specimen12-14. This was done by placing the specimen
film in a uniform magnetic field. The lines of
magnetic flux around the film form a closed path. The
cycle of magnetization of the film consisted of
magnetizing and demagnetizing the specimen. For
demagnetization a small steady current is passed
through the solenoid in series with the specimen film.
The direction of current is now reversed to complete
the magnetization-demagnetization cycle.
Results and Discussion
Fig. 1 shows the differential thermal analysis
(DTA) of polyaniline nano-crystalline magnetic thin
film doped with Fe, indicating the temperature of
evaporation around 288°C and at this temperature the
whole of Fe-doped polyaniline nano-crystalline
magnetic thin film converts into a thin film comparing
of nano-crystalline composites of polyaniline
nanocrystalline magnetic thin film and Fe-crystallites.
This process of evaporation re-polymerization of the
nano crystalline domain rich polymeric thin films.
Fig. 2 shows UV-visible spectra of undoped and
doped polyaniline. This spectrum shows the effect of
addition of Fe on the optical characteristics. The
addition of Fe in polyaniline nanocrystalline magnetic
thin film induces the formation of nano-composite
complex of Fe with polyaniline nano-crystalline host.
Fig. 2⎯UV visible spectra of un-doped and doped polyaniline
MATHUR et al.: VACUUM DEPOSITED MAGNETIC POLYANILINE THIN FILMS
355
Fig. 3⎯EDAX of polyaniline thin films
Fig. 5⎯Electron diffraction of Fe-doped polyaniline nanocrystalline magnetic thin films
Fig. 4⎯Surface topography of (a) un-doped and (b) doped
polyaniline nano-crystalline magnetic thin films
From Fig. 2, it can be seen that doping of polyaniline
with Fe has remarkable effect on optical absorption
spectra and position of the optical absorption peak.
Doping of polyaniline thin film by Fe also induces
crystallinity in the films, which is a direct evidence of
magnetizable nano-crystalline domains. Fig. 3 shows
the EDAX of polyaniline thin films indicating the
semi-amorphous and crystalline peaks of Fe doped
polyaniline nano-crystalline magnetic thin film. The
surface topography of undoped and doped polyaniline
nano-crystalline magnetic thin film is shown in Figs
4a and 4b. It is observed those magnetizable
crystalline domains are formed after annealing of the
Fe-doped thin films (Fig. 4b). The crystallinity of the
Fe-doped polyaniline nano-crystalline magnetic thin
film is shown in Fig. 5 (electron diffraction). These
thin films are highly magnetic as shown by the B-H
curve compared to a steel substrate Fig. 6. The degree
of magnetization is quite high. It can be observed that
due to specimen being thin film (1000 Å) sufficient
magnetization is achieved at low magnetic fields. The
same is confirmed by Fig. 7 showing ESR and EDMR
signal from Fe-doped polyaniline nano-crystalline
magnetic thin film. This signal also induces the
EDMR signal that may be fitted with a Lorentzian.
While the ESR signal is asymmetric as can be seen in
Fig. 7, the asymmetry in the line shape can have
different origins, possibly due to distribution of gfactor or spin diffusion related to a diverse conduction
mechanism in polyaniline magnetic thin films due to
polarons and bi-polarons. This may also give rise to
typical ESR lineshapes coming from structure of
guest host matrix structure arising out of Fe/
356
INDIAN J ENG. MATER. SCI., AUGUST 2004
Fig 6⎯B-H curve of polyaniline thin films
Fig. 8⎯The Mössbauer spectroscopic analysis of Fe-doped
polyaniline thin films
linearity in polyaniline thin films as reported earlier9. From these results it can be concluded that the
spectra show presence of dopant in polyaniline thin
films which further reveal complete homogenization
and paramagnetic behaviour of the film. The
Mössbauer spectroscopic analysis of Fe-doped
polyaniline thin films were carried out and Mössbauer
parameters were calculated from the graph which
showed isomeric shift 0.355 mm/s with respect to ∝Fe, quadrupole splitting 0.693 mm/s and linewidth
0.505 mm/s (Fig. 8).
11
Fig. 7⎯ESR and EDMR of Fe doped polyaniline nano-crystalline
magnetic thin film
polyaniline complexes in otherwise semiconducting
polyaniline base. EDMR signal is enhancing, i.e., Δ σ
> 0, as expected for conduction in polyaniline. The
EDMR signals come from the peculiarities of the
process of polaron hopping via paramagnetic sites. If
we assume that in a magnetic polymeric thin films,
the paramagnetic states are polarons and bi-polarons,
there are various types of hopping processes
associated with the various energy levels occupied by
the charged defects in polyaniline thin films, giving
rise to the observed signals having a broad
component. It is observed that for homogeneous
resonance lines the linewidth of ESR/EDMR signals
is inversely proportional to the spin-spin relaxation
time. Thus, for the broader component the relaxation
time is most probably shorter than for the narrower
line. For electric fields higher than 200 V/cm the
conductivity is found to increase exponentially with
the electric field, which is direct evidence of non-
Conclusions
The feasibility of preparation of vacuum deposited
magnetic nano-crystalline polyaniline thin films for
device applications has been established. The optical
absorption, ESR/EDMR study indicates the presence
of free charge carrier in the magnetic thin films. The
ESR studies and SEM study are indicative of presence
of magnetizable domains in the thin films. These
domains can be magnetized at low fields as indicated
by B-H curve. It can be concluded that vacuum
deposited polyaniline thin films hold potential for
being used as active magnetic devices for a wide
variety of applications including storage media,
magnetic bubble memory, switching and monitoring
of very small magnetic fields like those in biological
specimen.
Acknowledgements
The authors are grateful to Prof. Vikram Kumar,
Director, NPL, New Delhi for his interest in this
work.
MATHUR et al.: VACUUM DEPOSITED MAGNETIC POLYANILINE THIN FILMS
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