Heterogeneous phase formation in diluted magnetic semiconducting Zn 1-x-yCoxAlyO (CAZO) nanoparticles

Article abstract of DOI:10.1039/c4ra02973a

This article reports a systematic investigation of the synthesis and structural characterization of composite CAZO [(Zn_1-x-yCo _xAl_yO; x = 0.04, 0.03, 0.02; y = 0.01, 0.02, 0.03)] nanoparticles from combustion. The crystalline phase, morphology, size, and structure were characterized using X-ray diffraction (XRD), small and wide angle X-ray scattering (SAXS/WAXS), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The XRD and SAXS/WAXS analyses confirm the formation of the Co and Al co-doped ZnO hexagonal wurtzite structure with an additional metal oxide phase. The particle size and micro-strain were calculated by means of an integral breadth of X-ray diffraction lines. The selected area electron diffraction (SAED) patterns from TEM were correlated with the XRD patterns. The energy dispersive X-ray spectra (EDX) from SEM/TEM were recorded in order to analyze the composition of elements in the composite. The vibrational modes of the functional groups presented in the materials were assigned from FTIR and Raman spectra. The magnetic hysteresis measurement confirmed the room temperature ferromagnetism.

Full text of DOI:10.1039/c4ra02973a

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PAPER
Heterogeneous phase formation in diluted
magnetic semiconducting Zn1 Co Al O
ꢀxꢀy
x
y
Cite this: RSC Adv., 2014, 4, 23405
(CAZO) nanoparticles†
a
a
a
a
a
b
R. Siddheswaran,* R. Medlın, P. Belsky, V. Vavrunkova, J. Ocenasek, B. David
´ˇ
´
ˇ
´
ˇ
´
ˇ
a
and P. Sˇ utta
This article reports a systematic investigation of the synthesis and structural characterization of composite
CAZO [(Zn1ꢀxꢀyCo Al O; x ¼ 0.04, 0.03, 0.02; y ¼ 0.01, 0.02, 0.03)] nanoparticles from combustion. The
x
y
crystalline phase, morphology, size, and structure were characterized using X-ray diffraction (XRD), small
and wide angle X-ray scattering (SAXS/WAXS), scanning electron microscopy (SEM) and high resolution
transmission electron microscopy (HR-TEM). The XRD and SAXS/WAXS analyses confirm the formation
of the Co and Al co-doped ZnO hexagonal wurtzite structure with an additional metal oxide phase. The
particle size and micro-strain were calculated by means of an integral breadth of X-ray diffraction lines.
The selected area electron diffraction (SAED) patterns from TEM were correlated with the XRD patterns.
The energy dispersive X-ray spectra (EDX) from SEM/TEM were recorded in order to analyze the
composition of elements in the composite. The vibrational modes of the functional groups presented in
the materials were assigned from FTIR and Raman spectra. The magnetic hysteresis measurement
confirmed the room temperature ferromagnetism.
Received 3rd April 2014
Accepted 15th May 2014
DOI: 10.1039/c4ra02973a
www.rsc.org/advances
showed that ZnO doped with appropriate transition metals were
1
. Introduction
11–15
considered as diluted magnetic semiconductors
Zinc oxide is a signicant II–IV n-type semiconductor with a attracted a lot of interest due to their ferromagnetism at room
wide electronic band-gap (E
which
¼ 3.37 eV) and large free exciton temperature. Thus, zinc oxides of different morphologies with
g
binding energy (60 meV). Hence, it has been considered as a different dopant combinations are signicant and their appli-
good candidate for various applications, for example, gas cations are growing up. It is well known that ZnO materials are
sensors, photo-catalysts, ceramics, microwave absorbers, varis- widely used in various elds of science and technology using
16–23
tors, piezoelectric transducers, short wavelength optical different preparation methods.
Among the methods,
devices, solar cell windows, optical wave guides and spintronic combustion synthesis has many potential advantages such as
1
–9
devices.
ferromagnetism in diluted magnetic semiconductors has production rate, etc.
stimulated a great research interest for its potential applica- synthesis process was developed for the synthesis of
One of the recent studies of room temperature low processing cost, energy efficiency, relative simplicity, high
21,24,25 14
In our previous study, a combustion
10
x y
tions in spintronics and optoelectronics. ZnO nanostructures Zn1ꢀxꢀyCo Al O (CAZO) nanoparticles, where only the single
provide several opportunities for researchers to explore the phase formation was detected based on fast-scan XRD. Within
unique properties and applications. For semiconductors, present paper, we report in-depth analyses of the crystalline
doping and incorporation of metal elements is a powerful tool phase formation by slow-scan XRD, SAXS/WAXS and SAED
to tailor the electrical and optical properties for the construc- prole tting. Also, the surface morphology, particle size
tion of many optoelectronic devices. More interestingly, in distribution, elemental analyses and spectroscopic studies were
previous theoretical studies and experimental results have carried out.
a
New Technologies Research Centre, University of West Bohemia in Pilsen,
2
. Materials and methods
Plze nˇ -30614, Czech Republic. E-mail: rsiddhes@yahoo.com; rajendra@ntc.zcu.cz;
Preparation of [(Zn
0.02, 0.03)]
Co Al O; x ¼ 0.04, 0.03, 0.02; y ¼ 0.01,
Fax: +420377634702; Tel: +420-726914771
b
1ꢀxꢀy
x
y
CEITEC IPM, Institute of Physics of Materials, ASCR, v.v.i., Zi ˇz kova 22, CZ-61662
Brno, Czech Republic
Electronic supplementary information (ESI) available: Figures and information
about XRD, SAXS and Raman spectra of CAZO nanopowders, and also contains
gures of TEM micrographs of Zn0.95Co0.03Al0.02 and Zn0.95Co0.02Al0.03
nanocrystals. See DOI: 10.1039/c4ra02973a
ˇ
Initially, the CAZO nanoparticles were synthesized by citrate
nitrate auto-combustion (CNA) method using zinc nitrate
†
[Zn(NO
3
)
2
$6H
2
O], cobalt nitrate [Co(NO
3 2 2
) $6H O], and

O
O
aluminium nitrate [Al(NO
3
)
3
$9H O] as precursors, and citric
2
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acid [C
6
H
8
O
7
] as a fuel. The stoichiometric proportions of
The morphological features of the CAZO were observed by a
precursor metal nitrates were dissolved in de-ionized water. The scanning electron microscope (FEI Quanta 200 equipped with
amount of organic fuel (citric acid) was calculated from the EDX from EDAX) and the microstructures were recorded in
26
basic principle of propellant chemistry to be added with the detail using a high resolution transmission electron microscope
nitrates solution. The mixed solution was stirred well for 2 (JEM-2200FS equipped with EDX X-Max from Oxford instru-
ꢁ
hours at 60 C to achieve homogeneity, aerwards transferred ments). The Fourier transform infrared (FTIR) absorption
to platinum crucible and kept in a closed furnace maintaining a spectra were recorded using Nicolet-380 FTIR spectrometer
ꢁ
ꢀ1
constant temperature of 500 C. The combustion reaction was (Thermo Scientic) in the frequency range of 650–4000 cm
completed in a time span of 10 minutes and porous solid foam using ATR (attenuated total reection). Micro Raman spectro-
of nanopowders was obtained. The assumed reaction held scopic analyses were performed using the DXR Raman spec-
during the combustion process can be written as:
trometer (Thermo Scientic) with wavelength of the incident
beam 532 nm of Nd:YVO DPSS laser source. The spectra were
4
ꢀ1
(
1 ꢀ x ꢀ y)[Zn(NO
3
)
2
$6H
2
O] + x[Co(NO
3
)
2
$6H
2
O]
recorded for the wavenumber region 50–4000 cm , but the
CAZO absorbed and exhibited peaks only in the region 50–800
cm . The ferromagnetic hysteresis of the CAZO nanopowders
(1) was measure using a physical properties measurement system
PPMS, Quantum Design) in VSM mode.
+
y[Al(NO $9H
3
3
)
2
O] + (0.5583)x¼0.04,y¼0.01, (0.5611)x¼0.03,y¼0.02
,
ꢀ
1
(
0.5639)
[C H O ] ꢀ D / [Zn
Co Al O
x¼0.02,y¼0.03
6
8
7
1ꢀxꢀy
x
y
+
(N + CO + H O)[]
2 2 2
(
the eqn (1), the reactant mixture was set at the condition that
the value of oxygen balance is equal to zero. That is, the oxidizer
(
the NO
3
from the metals nitrate) completely and equivalently
3
. Results and discussion
reacts with the fuels (i.e., Zn, Co and Al with citric acid) without
requiring oxygen from any external source. The combusted
Structural characterization by X-ray diffraction
27
foams were crushed to obtain the nanopowder and then The main structure parameters (crystallite size and micro-
ꢁ
calcined at 600 C for 2 hours to obtain a fully crystalline strains) of the CAZO powders were investigated by X-ray
powder.
diffraction (XRD). Fig. 1 shows the X-ray diffraction patterns of
the CAZO synthesized with various Co and Al dopant levels. The
diffraction peaks of (100), (002), (101), (102), (110), (103), (200),
Characterization
(112), (201) and (004) planes were observed for all samples. All
the patterns t well with the hexagonal wurtzite type structure
corresponding to ZnO from the JCPDS card no.: 00-036-1451.
However, some additional phases corresponding to cobalt and
aluminium species were detected. The X-ray diffraction pattern
of Zn0.95Co0.02Al0.03O in comparison with different oxides of Zn,
Al and Co is shown in Fig. S1 of the ESI.†
The X-ray diffraction experiments were carried out using an
automatic powder X-ray diffractometer X'Pert Pro (PANalytical)
equipped with an ultra-fast linear semiconductor detector
PIXcel. Copper K
a
radiation (l ¼ 0.154 nm) was used as an
X-rays source. The ceramic alumina from NIST (National Insti-
tute of Standards and Technology) was used as an instrumental
standard.
According to JCPDS card no. 00-01-1307, the weak diffraction
ꢁ
ꢁ
peaks observed at angles 39.3 and 60.3 correspond to (222)
and (511) planes of Al O , respectively. A relatively weaker
The structure of the powder samples was investigated by
small and wide angle X-ray scattering (SAXS/WAXS) using the
2
3
2
ꢁ
diffraction peak observed at an angle 53.2 is indexed as (220)
plane of ZnO from the JCPDS card no. 00-13-0311. Also, the
SAXSess mc instrument (Anton Paar). The device uses a GeniX
Microfocus X-ray point source with a Cu anode (50 kV and 1
mA), single-bounce focusing X-ray optics and an advanced
collimation block. The experiments were performed in the
standard transmission setup (perpendicular incidence) and
imaging plates were used as detector. The scattering vector
2
ꢀ
1
range used for the experimental setup was 0.18–28 nm , i.e., it
covered both the SAXS and WAXS range simultaneously. The
scattering vector q is dened as q ¼ (4p/l)sin(2q/2), where l is
the X-ray wavelength and 2q is the scattering angle (with respect
to the incident beam). The sample exposition time was 10 min.
The powders were rst glued in between two pieces of scotch
tape which then was xed in the sample holder. The spectrum
of the scotch tape was measured as background. The 1D radial
intensity proles were created from the measured 2D scattering
images using the SAXS-quant soware (Anton Paar). Due to the
form of the samples (undened thickness of the powder
samples), it was not possible to calibrate the scattering inten-
sities on the absolute scale and hence the data are presented in
arbitrary intensity units (a.u.).
x y
Fig. 1 XRD pattern of the Zn1ꢀxꢀyCo Al O (CAZO) nanocrystals.
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Table 1 Size-strain results of the CAZO powders
The average crystallite size hDi in the direction perpendicular
to the diffracting lattice planes is
Zn0.95Co0.04Al0.01
O
Zn0.95Co0.03Al0.02
O
Zn0.95Co0.02Al0.03O
l
hDi ¼
;
(3)
Line hDi
hkl) [nm] h3i
hDi
hDi
f
C
b cos w
(
[nm] h3i
[nm] h3i
where l is the X-ray wavelength used and w is the Bragg's
1
0
1
1
1
1
1
2
00
02
01
02
10
03
12
01
37
30
27
19
28
18
32
24
0.00251
0.00257
0.00223
0.00224
0.00140
0.00133
0.00179
0.00129
35
25
23
21
30
19
24
22
0.00309
0.00330
0.00272
0.00303
0.00202
0.00226
0.00188
0.00170
26
18
21
19
24
21
28
25
0.00290
0.00309
0.00313
0.00350
0.00202
0.00283
0.00249
0.00228
angle.
The average micro-strain h3i in the diffracting volume is
dened as follows
f
G
b
h3i ¼ 4
:
(4)
tgw
ꢀ3
ꢀ3
ꢀ3
f
ꢂ27 ꢂ1.9 ꢃ 10
ꢂ25 ꢂ2.5 ꢃ 10
ꢂ23 ꢂ2.8 ꢃ 10
Evaluated crystallite size and micro-strains for the prom-
inent diffraction planes are given in Table 1. It is observed that
the particle size decreases with increase of aluminium content
and the micro-strain increases with decrease of the particles
size. This is due to smaller ionic radius of Al than Zn and Co.
ꢁ
ꢁ
weaker peaks observed at angles 44.8 and 65.2 are indexed as
(400) and (440) planes of Co
3 4
O , respectively (JCPDS: 00-80-
1532). But, these planes have comparatively negligible intensi-
Structural characterization by SAXS/WAXS analyses
ties rather ZnO planes. Shi in diffraction peaks and micro-
strains were calculated with respect to the standard ZnO
diffraction pattern. They are caused by interstitial or substitu-
tional impurities (doping) of metal ions of Co and Al in the
hosting sites. Since they exhibit majority of the peaks with
higher intensities corresponding to ZnO planes, it is considered
that the CAZO inherits the hexagonal wurtzite structure.
Therefore, it is determined that the CAZO nanocrystals are
formed as a composite of heterogeneous metal oxides.
The evolution of phase and size distribution of the CAZO
particles can be extracted by tting the SAXS/WAXS and the XRD
patterns. Fig. 2 shows the measured SAXS/WAXS proles on a
logarithmic scale. For all samples the intensity dependence in
30
the SAXS range follows the Porod's law very well (a power law
ꢀ
4
with exponent equal to ꢀ4: I ꢂ q ) expressing a very good
agreement with the theory for the high-q tail of scattering on
particles with a sharp interface (see the broken line at Fig. 2
representing the Porod's law). The average size of the particles
was observed greater than 25 nm, which is determined based on
the tting of particle size distributions to the experimental data
In powder X-ray diffraction, the position, height, integrated
intensity and FWHM are the main four parameters that char-
acterize the diffraction line proles. The broadening of a
diffraction line is a result of a real material structure, where the
size of the crystallites and the micro-strains are the most
important contributors to the broadening of the line. In this
study we used a procedure utilizing an integral breadth of a
31
using Irena program. It is a typical picture of small-angle
scattering of a powder with no signicant internal structure of
the material at nanometer scale (from about 1 nm to 20 nm).
In the WAXS range, four diffraction peaks were observed.
ꢀ1
28,29
The three peaks at q values of 22.5, 24.3, and 25.5 nm corre-
diffraction line.
Eqn (2) characterizes the integral breadth b
ꢁ
sponding to 2q angles of 32.0 (100), 34.7 (002), and 36.5 (101),
that includes two parameters namely the intensity I and the
0
respectively, originated from the ZnO (JCPDS: 00-036-1451) and
appeared for all samples (Fig. 2). These peaks can also be seen
integral intensity.
ð
1
b ¼ I Ið2wÞdð2wÞ
(2)
0
Ð
There, Iint ¼ I(2w)d(2w) is the integral intensity (area below
the line) and I is the maximal intensity of the diffraction line
0
I(2w). In general, the instrumental resolution of the equipment
has also to be taken into account in order to obtain a physical
(
depend only on the properties of the matter) component of
the broadening of the diffraction line. Furthermore, the
physical component of the integral breadth of the diffraction
line is a convolution of Cauchy and Gaussian components and
f
so it is necessary to perform de-convolution into a Cauchy b
C
f
and a Gaussian bG parts before the main real structural
parameters are determined. The Cauchy and Gaussian parts of
the integral breadth of the line correlate with the size of crys-
tallites and micro-strains, respectively. The average crystallite
size and micro-strains are determined using eqn (3) and (4),
2
9
respectively.
Fig. 2 SAXS/WAXS pattern for the CAZO nanoparticles.
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in the graphs in Fig. 1 from the XRD analysis. The peak at q ¼
ꢀ
1
ꢁ
8
.37 nm corresponding to 2q ¼ 11.8 (out of the range of the
XRD analysis) indicates the (101) plane of the Al O (JCPDS: 00-
2
3
016-0394) and appeared for all the combinations of
Zn1ꢀxꢀyCo
x
Al O. The two small broad humps around 4.5 and 14
y
ꢀ
1
nm were observed from the background (scotch tape), as can
be seen by comparison with its spectrum. As explained in the
experimental section, the scattering intensities are in arbitrary
units and thus, a quantitative comparison of the phase
composition of different samples cannot be compared directly.
Nevertheless, quantitative analysis was done by means of the
XRD studies.
Fig. 4 Raman spectrum of Zn0.95Co0.03Al0.02O, (a) experimental data
and fitted spectrum, and (b) decomposed fitted spectrum.
Fourier transform infrared spectroscopy (FTIR) analyses
The FTIR attenuated total reectance (ATR) absorbance spectra
of the CAZO samples are shown in Fig. 3. The apprehended
carbon and hydrogen during the combustion process and
organic impurities (which might remain adsorbed on the
surface of ZnO) due to sample processing are reasons to expect
C–H and C–O modes in the FTIR spectrum of this material. The
the molecules of multiple band structure in that region. The
ꢀ1
peak observed at 687 cm was assigned to Al–O vibration
ꢀ1
modes in Zn–O. The peaks observed between 850 and 900 cm
are caused by Co–O in Zn–O vibrations.
weak and broad asymmetrical absorption region at around 3400 Raman spectral characteristics
ꢀ
1
cm is likely due to the O–H vibrations from the physically
absorbed moisture in ambient atmosphere. The C–H stretching
modes of an aliphatic compound were observed between 2800
The measured and tted Raman spectra in Fig. 4a and b shows
the decomposed spectrum aer baseline correlation and
decomposition by least-square tting using Pearson's VII area
function for individual vibrational modes. ZnO wurtzite-type
ꢀ1
and 3000 cm . The sharper absorption peaks at 2850 and 2921
ꢀ
1
cm belong to symmetric and asymmetric vibrations of the
4
belongs to the space group C6V. According to the group theory,
ꢀ1
methylene group. The small shoulder at 2956 cm
assigned to methyl group. The weaker absorption peak observed
at 2350 cm is assigned to the CO stretching vibration from
2
ambient air. The absorption at ꢂ1600 cm was attributed to
the carbonyl group (C]O, stretching vibration). A narrow
strong peak at 1410 cm belongs to plain bending mode of C–
OH. Generally, similar C–H peaks have been observed in pure
ZnO powders and single crystals.
wavenumbers lower than 1100 cm
vibrations associated with Zn–O, Co–O and Al–O, but these
band are also overlapping with other ngerprint absorptions of
was
it has eight sets of phonon vibration modes of 2E
2
, 2A
modes are Raman inactive and
infrared active (silent modes). The A and E polar modes are
divided into transverse optical (TO) and longitudinal optical
LO) phonons (Raman and infrared active). Also, the two non-
1 1
, 2E and
34,35
2B
1
.
Among them, the 2B
1
ꢀ
1
1
1
ꢀ1
(
ꢀ1
polar E modes are Raman active. The Raman spectra of the
2
CAZO with various doping concentration have similar vibra-
tions as those shown in Fig. S3.†
32,33
In the spectral region with
ꢀ
1
were assigned for the
The characteristic bands of the wurtzite ZnO peaks observed
ꢀ1
ꢀ1
at 99 cm and 439 cm are assigned to E
TO phonon modes, respectively. The peak at 581 cm was
attributed to E (LO) mode in nanostructure due to the presence
of electric eld effects at surfaces, and TO branch of E
2 2
(low) and E (high)
ꢀ1
1
36
1
mode
was observed at 419 cm . Mode A (LO) usually around 580
cm is probably overlapped with E (LO), but for A (TO) mode
a weak line observed at 382 cm was assigned. Some other
weak vibrations observed at 332, 666 and 1154 cm (not seen in
Fig. 4) indicate the multi-phonon processes occurring in ZnO.
The presence of CoO compounds is indicated by bands centered
at around 176, 494, 529, 630, 702 and 721 cm . The vibrational
mode of CoO can occur in two phases of Co and Co with
ꢀ
1
1
ꢀ
1
1
1
1
ꢀ
ꢀ
1
37
ꢀ1
3
O
4
2 4
O
38
similar position of Raman modes.
Surface morphology and microstructure
The surface morphologies of the CAZO nanopowders prepared
by combustion synthesis are shown in Fig. 5. SEM observation
reveals that the CAZO nanopowder consists of porous and foam-
like morphology. It exhibits a homogenous morphology with
Fig. 3 FTIR spectra of the CAZO at different Co and Al concentrations. porous agglomerated structure. The porosity is assumed to
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Fig. 5 SEM micrographs of the CAZO nanopowder surface.
Fig. 7 HR-TEM micrographs of the Zn0.95Co0.04Al0.01O nanocrystals.
originate in the evaporation of gases during their decomposi-
tion. The energy dispersive X-ray spectra (EDX) of the CAZO
nanopowders are shown in Fig. 6 and report the presence of Zn,
Co, Al and O elements. The composition of the nanopowders
determined from EDX spectra shows a good agreement with the
stoichiometry of the solution.
The morphology, particles size and lattice planes of the
CAZO nanocrystals were analyzed by high resolution trans-
mission electron microscopy. The TEM and HR-TEM micro-
graphs are shown in Fig. 7 which conrms the formation of
hexagonal nanocrystals of ZnO. The size of the hexagonal sha-
ped particles varied in the range of 15–30 nm, while few of the
nanocrystals grown in z-direction bigger than average (with size
ꢂ100 nm) were found. The larger crystals are assumed to be
early formed nanocrystals which further grew during the
combustion and the calcination. Selected Area Electron
Diffraction (SAED) patterns were treated by Process Diffraction
39
soware. Data treatment included circular integration of
SAED intensities from TEM and calibration of the integrated
data intensity peaks by means of Camera Length (CL) for
comparison and indexation purposes with the standard Powder
Diffraction File (PDF). The SAED spectra in Fig. 8 conrmed the
Fig.
8 A plot of the comparison between SAED pattern of
2 3 3 4
Zn0.95Co0.04Al0.01O nanocrystals and standard ZnO, Al O and Co O
Fig. 6 SEM attached EDX spectra of the CAZO nanopowders.
X-ray diffraction patterns.
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M–H curve exhibits ferromagnetic nature with high remnant
magnetization with a small coercive eld and highly magne-
14
tized narrow hysteresis loop. The ferromagnetic hysteresis
increases with increase of Co concentration in the CAZO. For
the 2 at% of Co, the ferromagnetism was very small; it seems
almost like paramagnetic as shown in Fig. S7.† It was also found
that, no saturation magnetization is reached in any of the
samples with applied elds, which is ideal for spintronics.
4. Conclusions
The heterogeneous metal oxide composite nanoparticles of
Zn1 Co Al O were synthesised by CNA combustion method.
ꢀxꢀy
x
y
The prominent strong peaks of ZnO planes were identied from
XRD patterns conrm the formation of Co and Al co-doped ZnO
nanopowders. Additionally, minute peaks of (222) and (511)
planes of Al
2 3 2
O , (220) plane of ZnO , and (400) and (440) planes
of Co were observed. The presence of the shi in XRD peaks
3 4
O
and micro-strains correlate with the doping of Co and Al in Zn
sites. We conclude that both, the doping and individual metal-
oxides, were formed during the combustion synthesis process.
This composition was also conrmed by additional structural
analysis performed by means of SAXS/WAXS, Raman and FTIR.
The powder morphology, crystallite size, shape and inter-planar
distances were analysed by electron microscopy and diffraction.
The resulting particle size observed by SAXS was >20 nm, which
agrees with TEM micrographs. It also matches with the crys-
tallite size observed from XRD prole ranging from 18 to 37 nm.
Lattice deformation identied from the shi of XRD peaks
Fig. 9 EDX spectra of the CAZO nanocrystals from TEM.
diffraction of electrons from the ZnO lattice planes. The energy
dispersive X-ray spectra (EDX) from TEM were recorded in order
to conrm the elements in the composition. The EDX spectra
shown in Fig. 9 conrmed the presence of Zn, Co, Al and O in
the composition. Apart from these elements, the spectra
exhibited some elements such as Cu, C, Si which were present
in the carbon coated copper grid used as the sample holder.
ꢀ3
corresponds to average micro-strain of about 2.5 ꢃ 10 . It was
concluded that the combustion synthesised powder consists of
x y
Co and Al co-doped ZnO (Zn1ꢀxꢀyCo Al O; i.e., CAZO), and a
minute quantities of heterogeneous metal oxide phases of Zn,
Co and Al. It was also found that, the CAZO exhibits room
ferromagnetic hysteresis, which increases with Co content.
Room temperature ferromagnetism
The room temperature magnetic hysteresis (M–H) curve for the
ꢁ
14
CASO nanoparticles calcined at 600 C is shown in Fig. 10. The
Acknowledgements
The result was developed within the CENTEM project, reg. no.
CZ.1.05/2.1.00/03.0088 co-funded by the ERDF as part of
Ministry of Education, Youth and Sports OP RDI programme.
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