Effect of synthesis method on the ferromagnetic
behavior ZnO nanoparticles
MdGazzali P.M.*, SoumyaRajan, G.Chandrasekaran
Department of Physics, Pondicherry University, R. Venkataraman Nagar, Kalapet, Pondicherry-605014, India
*
Corresponding author’s e-mail:gazzali313@gmail.com, Tel.: +91-9444905538
ℎ𝑖𝑔ℎ
Abstract
We report a comparative study of chemically
synthesized and ball milled ZnO in order to understand
the role of defects and lattice strain. Important conclusion
has been drawn from the results of structural, optical and
magnetic studies.
Keywords:
Nanoparticles,
autocombustion. XRD, VSM
bill-milling,
sol-gel
Introduction
ZnO has attracted considerable attention as a
semiconducting material with wide direct band gap and
large exciton binding energy at room temperature.
Extensive research on ZnO confirmed that it is a proper
candidate to be used in the field of electronics, gas
sensors,photovoltaics, electrochemistry and thin film
transistors. The various properties of ZnO depend on the
composition and morphology and defect structure [1]. It
is well known that the oxygen vacancies affect the
properties of ZnO significantly. In this work we applied
XRD, Raman and UV measurements to study the defect
induced ferromagnetism in mechanically activated and
chemically prepared samples.
Experimental
The commercial ZnO powder (Himedia A.R.
99.5 %) is mechanically milled in a planetary ball mill
for two different milling times, 150 and 300 minutes
and designated as bulk, ZnO-150 and ZnO-300. ZnO
NPs are also prepared by sol-gel auto-combustion
method with zinc nitrate and glycine as precursors and
designated as ZnO-CM. The phase identification of the
samples is determined using X’Pert PRO X-ray
Diffractometer with Cu-Kα radiation. Raman scattering
measurements are recorded using confocal microRaman microscope (Renishaw inVia Reflex) in the
range 100–1400 cm-1 with an excitation wavelength of
514.5 nm. Room temperature M-H loop measurements
are carried out using Vibrating Sample Magnetometer
(Lakeshore VSM 7410). UV-Vis absorption /
reflectance measurements are made by Lambda 650
UV-Vis diffuse reflectance spectrometer (PerkinElmer).
Results and discussions
X-Ray diffraction patterns all the samples are
coinciding with the peaks of ZnO wurtzite structure
(JCPDS No: 01-075-0576). Particle size, lattice strain
and lattice constants are calculated. The observed shift
and enhancement of FWHM of 𝐸2
~ 438 cm-1 and
E1(LO) ~ 586 cm-1 phonon modes in the Raman spectra
may be attributed to the increased defect density
concentration and lattice strain [2]. UV studies show a
decrease in band gap energy (Eg) with the lowest value
(3.21 eV) for the ZnO-150 sample.The observed red
shift of Eg may be induced by electrons generated from
oxygen vacancies [3]. VSM measurements confirm the
soft ferromagnetic (FM) nature in all the samples.
Magnetization is found to increase with the increase in
milling time. But the ZnO-CM shows the highest
magnetization of 126 memu/g and coercivity of 141 Oe
among our samples. This controversy may be attributed
to the presence of residual carbon in the chemically
prepared ZnO lattice [4].
Conclusion
The structural characterization of the starting
ZnO powder and its variation upon by mechanical
activation and chemical preparation are performed by
XRD and Raman scattering measurements. The band
gap energy variation of the samples reflects the impact
of intrinsic and extrinsic defects. The occurrence of
oxygen vacancies induces FM in the investigated
samples.
Reference
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