Effect depositions parameters on the characteristics of Ni0.5Co0.5Fe2O4 nanocomposite films prepared by DC reactive magnetron Co-Sputtering technique

Abstract

In this work, spinel ferrites (NiCoFe2O4) were prepared as thin films by dc reactive dual-magnetron co-sputtering technique. Effects of some operation parameters, such as inter-electrode distance, and preparation conditions such as mixing ratio of argon and oxygen in the gas mixture, on the structural and spectroscopic characteristics of the prepared samples were studied. For samples prepared at inter-electrode distance of 5 cm, only one functional group of OH- was observed in the FTIR spectra as all bands belonging to the metal-oxygen vibration were observed. Similarly, the XRD results showed that decreasing the pressure of oxygen in the gas mixture lead to grow more crystal planes in the samples prepared at inter-electrode distance of 5 cm. The energy band gap was determined for the sample prepared with mixing ratio of 65:35 and found to be 2.7, 2 and 3.35 eV for direct allowed, direct forbidden and indirect allowed transitions, respectively. The high structural purity was confirmed as no traces for any elements other than Co, Ni, Fe and O were found in the final samples.

Full text

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
76
Effect depositions parameters on the characteristics of Ni0.5Co0.5Fe2O4
nanocomposite films prepared by DC reactive
magnetron
Co-Sputtering technique
Tawfiq S. Mahdi and Firas J. Kadhim
Department of Physics, College of Science, University of Baghdad, Baghdad, Iraq
E-mail: dr.firas90@yahoo.com
Corresponding author: tawfik.s28@gmail.com
Abstract
Keywords
In this work, spinel ferrites (NiCoFe
2
O
4
) were prepared as thin
films by dc reactive dual-magnetron co-sputtering technique. Effects
of some operation parameters, such as the distance between
electrodes (inter-electrode distance), and preparation conditions such
as gas mixing ratio of argon and
oxygen, on the structural and
spectroscopic characteristics of the prepared samples were studied.
For samples prepared at an inter-electrode distance of 5 cm, only one
functional group of OH- was observed in the FTIR spectra as all
bands belonging to the metal-
oxygen vibration were observed.
Similarly, the XRD results showed that decreasing the pressure of
oxygen in the gas mixture leads to grow more crystal planes in the
samples prepared at an inter-electrode distance of 5 cm. The energy
band gap was determined for the sample prepared with a mixing ratio
of 65:35 and found to be 2.7, 2, and 3.35 eV for direct allowed, direct
forbidden, and indirect allowed transitions, respectively. The high
structural purity was confirmed as no traces for any elements other
than Co, Ni, Fe, and O were found in the final samples.
Magnetron
sputtering, reactive
sputtering, spinel
ferrite, thin films
Article info
.
Received: Mar. 2020
Accepted: May. 2020
Published: Jun. 2020
ﻱﻮﻧﺎﻨﻟﺃ ﺐﻛﺍﺮﺘﻤﻟﺍ ﺔﻴﺸﻏﺃ ﺺﺋﺎﺼﺧ ﻰﻠﻋ ﺐﻴﺳﺮﺘﻟﺍ ﺕﻼﻣﺎﻌﻣ ﺮﻴﺛﺄﺗNi0.5Co0.5Fe2O4
ﻙﺮﺘﺸﻤﻟﺃ ﻲﻠﻋﺎﻔﺘﻟﺃ ﻲﻧﻭﺮﺘﻨﻛﺎﻤﻟﺃ ﺬﻳﺫﺮﺘﻟﺃ ﺔﻴﻨﻘﺗ ﺔﻄﺳﺍﻮﺑ ﺓﺮﻀﺤﻤﻟﺃ
ﻱﺪﻬﻣ ﺢﻟﺎﺻ ﻖﻴﻓﻮﺗﻭ ﻢﻅﺎﻛ ﺩﺍﻮﺟ ﺱﺍﺮﻓ
ءﺎﻳﺰﻴﻔﻟﺍ ﻢﺴﻗ، ﻡﻮﻠﻌﻟﺍ ﺔﻴﻠﻛ، ﺩﺍﺪﻐﺑ ﺔﻌﻣﺎﺟ ،ﺩﺍﺪﻐﺑ، ﻕﺍﺮﻌﻟﺍ ﺔﺻﻼﺨﻟﺍ ﻞﻜﻴﻧ ﺐﻛﺮﻣ ﺮﻴﻀﺤﺗ ﻯﺮﺟ ،ﺚﺤﺒﻟﺍ ﺍﺬﻫ ﻲﻓ- ﺔﻴﻨﻘﺗ ﺔﻄﺳﺍﻮﺑ ﺔﻘﻴﻗﺭ ﺔﻴﺸﻏﺃ ﻞﻜﺷ ﻰﻠﻋ ﻲﻟﺰﻐﻤﻟﺍ ﺖﻳﺍﺮﻴﻓ ﺖﻟﺎﺑﻮﻛ
ﻦﻴﺑ ﺎﻣ ﺔﻓﺎﺴﻤﻟﺍ ﻞﺜﻣ ،ﻞﻴﻐﺸﺘﻟﺍ ﺕﻼﻣﺎﻌﻣ ﻦﻣ ﺩﺪﻋ ﺮﻴﺛﺄﺗ ﺔﺳﺍﺭﺩ ﻢﺗ .ﺮﻤﺘﺴﻤﻟﺍ ﻲﻠﻋﺎﻔﺘﻟﺍ ﻲﻧﻭﺮﺘﻨﻛﺎﻤﻟﺍ ﻙﺮﺘﺸﻤﻟﺍ ﺬﻳﺫﺮﺘﻟﺍ
ﻲﻓ ﻦﻴﺠﺴﻛﻭﻷﺍﻭ ﻥﻮﻛﺭﻵﺍ ﻱﺯﺎﻏ ﺐﺴﻧ ﻞﺜﻣ ،ﺮﻴﻀﺤﺘﻟﺍ ﻑﻭﺮﻅ ﻚﻟﺬﻛﻭ ﻦﻴﺒﻄﻘﻟﺍ ﺺﺋﺎﺼﺨﻟﺍ ﻰﻠﻋ ،ﺔﻳﺯﺎﻐﻟﺍ ﺔﻄﻠﺨﻟﺍ
.ﺓﺮﻀﺤﻤﻟﺍ ﺕﺎﻨﻴﻌﻠﻟ ﺔﻴﻔﻴﻄﻟﺍﻭ ﺔﻴﺒﻴﻛﺮﺘﻟﺍﻲﻓ ﻦﻴﺒﻄﻘﻟﺍ ﻦﻴﺑ ﺎﻣ ﺔﻓﺎﺴﻣ ﺪﻨﻋ ﺓﺮﻀﺤﻤﻟﺍ ﺕﺎﻨﻴﻌﻟﺍ 5cm ﻢﻤﻘﻟﺍ ﺕﺮﻬﻅ
ﺔﻋﻮﻤﺠﻤﻟ ﺩﻮﻌﺗ ﺓﺪﻴﺣﻭ ﺔﻤﻘﻟ ﺔﻓﺎﺿﺇ ﺏﻮﻠﻄﻤﻟﺍ ﺐﻛﺮﻤﻟﺍ ﺕﺎﺌﻳﺰﺟ ﺕﺯﺍﺰﺘﻫﻻ ﺓﺪﺋﺎﻌﻟﺍ
-
OH ﺩﻮﻴﺣ ﻁﺎﻤﻧﺃ ﺕﺮﻬﻅﺃ ﺎﻤﻛ
ﺔﺒﺴﻧ ﻞﻴﻠﻘﺗ ﻥﺃ ﺔﻴﻨﻴﺴﻟﺍ ﺔﻌﺷﻷﺍ ﻯﺮﺟ .ًﺍﺩﺪﻋﺮﺜﻛﺃ ﺔﻳﺭﻮﻠﺑ ﺕﺎﻳﻮﺘﺴﻣ ﻮﻤﻨﻟ ﻯﺩﺃ ﺔﻳﺯﺎﻐﻟﺍ ﺔﻄﻠﺨﻟﺍ ﻲﻓ ﻦﻴﺠﺴﻛﻭﻷﺍﺯﺎﻏ
ﺔﻳﺯﺎﻐﻟﺍ ﺔﻄﻠﺨﻟﺍ ﻡﺍﺪﺨﺘﺳﺎﺑ ﺓﺮﻀﺤﻤﻟﺍ ﺕﺎﻨﻴﻌﻠﻟ ﺔﻗﺎﻄﻟﺍ ﺓﻮﺠﻓ ﺔﻤﻴﻗ ﺪﻳﺪﺤﺗ 65:36 ﺖﻐﻠﺑﻭ 2.7 eV ﺕﻻﺎﻘﺘﻧﻼﻟ
ﻭ ﺔﺣﻮﻤﺴﻤﻟﺍ ﺓﺮﺷﺎﺒﻤﻟﺍ 2 eV ﻭ ﺔﺣﻮﻤﺴﻤﻟﺍ ﺮﻴﻏ ﺓﺮﺷﺎﺒﻤﻟﺍ ﺕﻻﺎﻘﺘﻧﻼﻟ eV 3.35 ﺷﺎﺒﻤﻟﺍ ﺮﻴﻏ ﺕﻻﺎﻘﺘﻧﻼﻟ ﺓﺮ
ﺍﺪﻋ ﺎﻣ ﻯﺮﺧﺃ ﺮﺻﺎﻨﻌﻟ ﺭﺎﺛﺁ ﺔﻳﺃ ﺮﻬﻈﺗ ﻢﻟ ﺫﺇ ﺓﺮﻀﺤﻤﻟﺍ ﺐﻴﻛﺍﺮﺘﻠﻟ ﺔﻴﻟﺎﻌﻟﺍ ﺔﻴﺒﻴﻛﺮﺘﻟﺍ ﺓﻭﺎﻘﻨﻟﺍ ﺪﻴﻛﺄﺗ ﻢﺗ .ﺔﺣﻮﻤﺴﻤﻟﺍ
ﺔﻴﺋﺎﻬﻨﻟﺍ ﺕﺎﻨﻴﻌﻟﺍ ﻲﻓ ﻦﻴﺠﺴﻛﻭﻷﺍﻭ ﺪﻳﺪﺤﻟﺍﻭ ﻞﻜﻴﻨﻟﺍﻭ ﺖﻟﺎﺑﻮﻜﻟﺍ.
DOI: 10.20723/ijp.18.45.76-88

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
77
Introduction
Ferrites are compound of mixed
oxides of iron and one or more other
materials which have ferrimagnetic
properties. Ferrites are regarded as
good magnetic materials because of
their higher resistivity, low cost, easy
manufacturing, and favorable magnetic
properties [1]. They are extensively
used as permanent magnets,
transformer core, high-frequency
application, and microwave devices
[2]. These compounds have several
types based on the crystal structure,
like spinel ferrite, garnet ferrite,
hexagonal ferrite, and other ferrites [3].
The first type (spinel ferrite) is the
class of oxide materials with
remarkable electrical and magnetic
properties, which have been
investigated and applied during the last
few decades. Due to their magnetic
properties, spinel ferrites have various
applications in numerous fields
including microwave devices,
recording media, magnetic fluids, gas
sensors, high-density information
storage, ferrofluids, and catalysts [4].
In spinel cubic structured ferrites,
MFe2O4 (M= Mn2+, Co2+, Ni2+, Zn2+,
etc.) here in, oxygen forms face-
centered cubic (f.c.c.) closed packing
and M2+ and Fe3+ occupy either
tetrahedral (A) or octahedral (B)
interstitial sites [5]. The magnetic
properties of ferrite nanoparticles also
get influenced by the method of
synthesis and process parameters even
though the common diagnostic tools,
such as XRD, show similar crystalline
structure [6]. It is known that the
magnetic properties depend on the site
occupancies by the magnetic ions [7].
Cobalt and nickel, both the ferrites,
belong to the category of inverse spinel
ferrites. Therefore, by substituting the
Co2+, Ni2+, and/or Fe3+ ions by suitable
cations, their structures undergo a
change from inverse spinel to mixed
spinel, leading to a corresponding
change in the magnetic properties.
Thus, by the choice of the cations as
well as their distribution in tetrahedral
and octahedral sites of the lattice,
interesting and useful magnetic
properties can be obtained [8].
Following what was mentioned above
regarding the various types of ferrite,
the composition under research aims to
put both Co and Ni together in a stable,
usable composition through which soft,
high-magnetization alloy is widely
used for recording head poles, thin-
film inductors or transformers.
NiCoFe2O4 alloys have been
demonstrated to have a low coercively
and high-saturation magnetization [9].
NiCoFe2O4 ternary alloys, rich in Fe,
have also been noted for their low
thermal expansion property, and
commercial applications of these
alloys include microwave guides,
spacecraft optics, laser housings, and
printed wired boards [10]. At the same
time, the hard facing alloys based on
Co or Ni have used for their high
mechanical and chemical properties
especially their wear and corrosion
resistance at high temperatures [11].
Also, NiCoFe2O4 can be used as a
binder with unique properties [12].
This binder when subjected to plastic
deformation, it substantially maintains
its face-centered cubic (f.c.c.) crystal
structure and avoids stress and/or
strain-induced transformations [13].
Cobalt ferrite (CoFe2O4) is a well-
known hard magnetic material with
high coercively and moderate
magnetization, which is useful in high-
density digital recording discs and
audio/videotape. However, CoFe2O4
has a high magneto crystalline
anisotropy, which makes it difficult to
achieve high initial susceptibility or
magnetic conductivity [14], while
nickel ferrite (NiFe2O4) is a typical soft
magnetic material with lower magneto
crystalline anisotropy [15]. It provides
an effective way to reduce the

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
78
anisotropy of CoFe2O4 by partly
substituting Co2+ for Ni2+, NiCoFe2O4.
In view of the above, a new type of
nanocomposite, NiCoFe2O4, which has
controllable magnetic properties, is
expected to be used in electromagnetic
and nanotechnology applications.
Amongst all inverse spinel ferrites, the
nickel substituted cobalt ferrite has
been extensively studied in view of
their good chemical and thermal
stability, high electrical resistivity,
magnetic anisotropy, high coercivity,
and moderate saturation magnetization,
various exchange interactions and
super-paramagnetism, etc. In addition,
they exhibit ferrimagnetism,
originating from the magnetic moment
of anti-parallel spins between Fe3+ ions
at tetrahedral sites and Co2+ or Ni2+
ions at octahedral sites [16].
Co-sputtering of materials offers an
important alternative to complex and
sometimes impossible alloying of
metallic materials for a single
sputtering target [17, 18]. Up to now,
co-sputtering was accomplished with
either two small, usually round
cathodes [19, 20] or a multicomponent,
tailored target [21].
Experimental part
Spinal ferrites thin films were
deposited onto glass substrate using
lab-made dc reactive closed-field
unbalanced dual magnetron
(CFUBDM) co-sputtering technique. A
high purity cobalt and nickel (99.99%)
targets were mounted on the cathode
according to a geometrical
arrangement. The geometrical
arrangement shown in Fig.1 was
proposed according to a numerical
treatment carried out to determine the
dimensions of both sheets with respect
to each other to achieve the required
doping process. This numerical
treatment was performed by applied
Modeling Lab. at using Q-point
Software produced by TimX
Company, Japan. Both electrodes
(cathode and anode) were made of
stainless steel with 10 cm diameter and
4 mm thickness which were placed
parallel to each other and the anode
could be vertically moved to adjust the
distance between target and substrate.
The electrodes were connected to dc
power supply to provide the required
electric power. The plasma was
generated by the electric discharge of
argon gas while the oxygen gas with a
purity of 99.99% was used as a
reactive gas. The mixing ratio of both
gases was controlled using a stainless
steel mixer before and flowed into the
deposition chamber. The deposition
chamber was evacuated to base
pressure about 2x10-2 mbar by an
Edward double-stage rotary pump with
a suction power of 8 m3/hr to reduce
uncontrolled contamination during the
experiment to minimum concentration.
The pressure during the operation was
kept to a constant value of
approximately 5x10-2 mbar, several gas
mixing ratios were used for each inter-
electrode distance. When the inter-
electrode distance is 4 cm, gas mixing
ratios Ar:O2 were 50:50, 60:40, 75:25
and 80:20 while the mixing ratios were
50:50, 55:45, 60:40, and 65:35 for
inter-electrode distance of 5 cm.
Crystallographic and the optical
characteristics of the prepared samples
were determined by the Fourier-
transform (FTIR), standard x-ray
diffraction (XRD) analysis, Scanning
electron microscopy (SEM), Energy
Dispersive X-ray Diffraction (EDX),
and UV-Visible spectroscopic. The
final samples presented in this work
were prepared without heat treatment
of the cathode and the anode for
2 hours of deposit time.

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
79
Fig.1: Geometrical arrangement of the
co-sputtering using Ni, Co, and Fe target.
Results and discussion
The FTIR spectra recorded in the
range of 400-4000 cm-1 are shown in
Fig.2. The bands of solids are usually
assigned to the vibration of ions in the
crystal lattice. There are two main
frequency bands, namely, the high-
frequency band (ν1) is observed at
584 cm-1 to 610 cm-1 whereas the
lower frequency band (ν2) is observed
at 412 to 418 cm-1 [22]. These two
observed bands ν1 and ν2 correspond to
the intrinsic vibrations of tetrahedral
and octahedral complexes,
respectively, following the main
characteristics of all the ferrite material
[23]. The broad metal-oxygen (M-O)
bands are observed in the infrared
spectra of samples with a gas mixing
ratio (50:50, 60:40, 75:25, and 80:20).
The band (ν1) in 600–550 cm–1 region
which seen in all gas mix ratio samples
were detected due to tetrahedral metal-
oxygen (CoFe2O4, NiFe2O4) stretching
vibration [23]. The absence of obvious
peak that due octahedral coordinated
metal ions had been noticed and that an
indication to lower frequency band (ν2)
expected to be around 400 cm-1 only in
gas mix ratio (80:20) where observed
at 412-450 cm-1. This probably caused
by the broadening of this peak
attributed to very small particles of
spinel ferrites [24].
From that point in contrast of the
samples prepared at different gas
mixing ratios (50:50, 55:45, 60:40,
65:35) and 5 cm the inter-electrode
distance, as shown in Fig.3, and that
lead to the clear observation of
the broad metal-oxygen (CoFe2O4,
NiFe2O4) bands at 400-477 cm-1, 508-
604 cm-1 excepted in the gas mixing
ratio (50:50) on the other side the
characteristics of vibrational bands of
(NiCoFe2O4) composite are found
in the FTIR spectra located around
508 cm-1, 1368 cm-1, and 1638 cm-1 in
the sample with gas mix ratio (65:35).
From all that has been mentioned
above, the two strong bands can be
recognized. The first one is around
1638 cm-1 attributed to the bending
vibrations of (O-H) band which also is
overlapping with that in (NiCoFe2O4)
composite, while the second-wide band
peak at 3451 cm-1 s is assigned to the
stretching modes of the free or
adsorbed water vapor. This adsorption
has resulted during the testing process
as the deposition process was
confirmed by the XRD patterns to
produce highly-pure structures [25].

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
80
Fig.2: FTIR spectra for samples prepared at inter-electrode distance of 4 cm.
400900140019002400290034003900
Transmittance (%)
Wavenumber (cm-1)
4cm
50-50
60-40
75-25
80-20

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
81
Fig.3: FTIR spectra for samples prepared at inter-electrode distance of 5 cm.
400900140019002400290034003900
Transmittance (%)
Wavenumber (cm-1)
5cm
50-50
55-45
60-40
65-35

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
82
Using both inter-electrode distances
(4 and 5) cm and several gas mixing
ratios, the spinel structures were
observed in the XRD patterns, as
shown in Figs. 4 and 5. The XRD
analysis of sample prepared at inter-
electrode distance of 4 cm and gas
mixing ratios Ar:O2 of 50:50 and 60:40
showed the presence of six
characteristic peaks at 30.32°, 35.60°,
37.06°,43.22°, 53.76°, and 57.48°.
These peaks are corresponding to
Miller indices (220), (311), (222), (400),
(422), and (510), respectively for the
spinel α-ferrite [26]. This confirms the
formation of spinel simple cubic
structure (JCPDS, No. 86-2267, Fd-
3m) while the samples prepared using
mixing ratios of 75:25 and 80:20, there
was no evidence on the formation of
spinel structure except CoF2O4, which
was observed in the sample prepared
using mixing ratio of 75:25 without the
formation of NiF2O4. This can be
attributed to the fact that the Ni2+ ion
(radius of 0.78Å) is smaller than Co2+
ion (radius of 0.82Å) [27]. On the
other hand, the samples prepared at
inter-electrode distance of 5 cm with
mixing ratios of 50:50, 55:45, 60:40,
and 65:35 showed all peaks assigned to
the formation of spinel α-ferrite, in
addition to the NiCoF2O4 as single-
phase cubic spinel structure, especially
for mixing ratio of 65:35, as confirmed
by JCPDS card (1-1221). No peaks of
impurities could be observed, which
confirms the high purity of prepared
samples. The average grain size of the
composite was estimated using Debye-
Scherer’s equation [28]
=.
   (1)
where D is the grain size, 0.89 is the
Scherrer’s constant, λ is the x-ray
wavelength, β is the full-width at half
maximum (FWHM) and θ is the
corresponding Bragg's angle. The
average grain size of the sample
prepared with a mixing ratio of 65:35
was found to be 14.43 nm.
The scanning electron microscopic
image of all the synthesized samples
was shown in Fig.6. The images show
that the particles have an almost
homogeneous distribution, and some of
them are in agglomerated form. Also
the micrographs show the presence of a
number of interfaces. It is evidenced by
SEM images that the aggregation of
particles lies in the nanometric region.
The average grain size for the prepared
sample varies from 26.86 nm to 40.82
nm. It was noted that the average grain
size of the samples obtained from SEM
images is larger than nanocrystal size
calculated from the XRD
measurements, which indicates that
each grain is formed by aggregation of
a number of nanocrystals. The shape of
the formed nanoparticles could not be
determined due to the limited
resolution of the measuring instrument
to 200nm. The particles were observed
as uniform grains (in different SEM
images) confirming the crystalline
structure of Ni-Co ferrite which were
detected by XRD studies.

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
83
Fig.4: X-ray diffraction (XRD) of samples prepared at inter-electrode distance of 4 cm
10 20 30 40 50 60 70 80
Intensity
2ɵ(degree)
4cm
50-50
60-40
75-25
80-20

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
84
Fig.5: X-ray diffraction (XRD) of samples prepared at inter-electrode distance of 5 cm.
(220)
(311)
(400) (422) (511) (440)
10 20 30 40 50 60 70 80
Intensity
2ɵ(degree)
5cm 50-50 55-45 60-40 65-35

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
85
Fig.6: SEM of the nanostructured NiCoFe2O4 thin film prepared using Ar: O2 gas mixture of 65:35.
The EDX is an analytical technique
used for the elemental analysis or
chemical characterization of the
prepared sample. It relies on
interaction of x-ray excitation and a
solid sample. Its characterization
capabilities are due in large part to the
fundamental principle that each
element has a unique atomic structure
allowing a unique set of peaks on its
electromagnetic emission spectrum. It
was essential to check the chemical
composition of the sample, so the
required compound (Ni0.5Co0.5Fe2O4)
prepared with a gas mixing ratio
(Ar:O2) of 65:35 and inter-electrode
distance of 5 cm was confirmed by
EDX. The qualitative composition of
the prepared samples as well as the
quantitative presence of Co, Ni, Fe,
and O in these samples are presented in
Fig.7 and the percentage elemental and
atomic amounts of these elements are
given in Table1. This result confirms
the stoichiometry of the prepared
compound. Also, no trace of any
impurity was found in the EDX
spectrum which confirms the high
structural purity of the synthesized
material.
Fig.7: EDX result of NiFe2O4 sample prepared using Ar:O2 gas mixture of 65:35.

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86
Table1: Element of each sample composition Ni-Co ferrite analyses by (%weight).
NiCoFe2O4 Composite
Ni
Co
Fe
O
Sum
wt. %
8.26
9.93
53.25
28.57
100%
A %
4.61
5.53
31.28
58.58
100%
B.E
4.47
4.43
4.34
The reactive dc dual-magnetron
sputtering technique is a convenient
way for obtaining a homogeneous tiny
spinel ferrite (Ni ferrite, Co ferrite) and
mixed spinel ferrites. The process
involves no impurity pickup or
material loss.
The absorption spectra of the
prepared samples were recorded in the
spectral range of 300-800 nm at room
temperature as illustrated in Fig.8. The
absorbance increases with increasing
of argon pressure in the gas mixture
(i.e., decreasing oxygen pressure) and
this behavior is similar to that of
samples prepared at different
conditions, such as inter-electrode
distance of 5 cm, and gas mixing ratio
of 50:50, 55:45, 60:40, and 65:35 after
the same deposition time. This increase
in absorbance agrees to Beer-Lambert
law as longer deposition time leads to
increase film thickness, which
represents the sample length in the law.
Fig.8: Absorption spectra of prepared samples of thin film using different gas mixing ratios
and different deposition time at two inter-electrode distances (4cm and 5cm).

Iraqi Journal of Physics, 2020 Tawfiq S. Mahdi and Firas J. Kadhim
87
From the last figures, the prepared
samples exhibit high absorption at the
spectral region shorter than 300 nm
and an absorption edge at about 320
nm. The energy bandgap of the ternary
(NiCoF2O4) sample prepared with the
mixing ratio of (65:35) can be
calculated by:
 =   
 (2)
where α is the absorption coefficient,
Eg is the energy band gap, A is
constant, and n is a given value
depends on the nature of the optical
transition (allowed direct, allowed
indirect, forbidden direct, or forbidden
indirect). The intercept of linear
behavior of (αhν)2, (αhν)1/2 and (αhν)3/2
versus hν assigns that the direct
(allowed and forbidden) and indirect
transitions, respectively, are the
dominant as shown in Fig.9 and
determines the energy band gap of the
prepared material [29].
Fig.9: Determination of indirect energy band gap for (NiCoF2O4) samples prepared using
gas mixture ratio 65:35 (a) indirect transition and (b) direct transition.

Iraqi Journal of Physics, 2020 Vol.18, No.45, PP. 76-88
88
Conclusions
Highly-pure spinel ferrites
(Ni0.5Co0.5Fe2O4) were synthesized by
the dc reactive magnetron co-
sputtering technique. The high
structural purity of the prepared
samples was confirmed by the
characterization as no impurities were
found in the final sample. The fine
control of the structural compositions
could be performed by controlling both
operation parameters and preparation
conditions of the co-sputtering system.
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