Structural, Magnetic Properties of Wide Band Gap Oxide Semiconductors by MMSE Journal

Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Structural, Magnetic Properties of Wide Band Gap Oxide Semiconductors46 B. Balaraju1, M. Kuppan1, S. Harinath Babu2, S. Kaleemulla1,a, N. Madhusudhana Rao1, C. Krishnamoorthi1, Girish M. Joshi3, G. Venugopal Rao4, K. Subbaravamma5, I. Omkaram6, D. Sreekantha Reddy7 1 – Thin films Laboratory, Centre for Crystal Growth, VIT University, Vellore-632014, Tamilnadu, India 2 – Department of Physics, Annamacharya Institute of Technology and Sciences, New Boyanapalli, Rajampet-516 126 andhra Pradesh, India 3 – Polymer Nanocomposite Labrotory, Centre for Crystal Growth, VIT University, Vellore-632014, Tamilnadu, India 4 – Materials Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam-603102, Tamilnadu, India 5 – Department of Physics, AMET University, Kanthur, Chennai-603112, Tamilnadu, India 6 – Department of Electronics and Radio Engineering, KyungHee University, Yongin-si, Gyeonggi-do 446-701, Republic of Korea 7 – Department of Physics and Sungkyukwan Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwan – 440746, Republic of Korea a – skaleemulla@gmail.com DOI 10.2412/mmse.95.56.253 provided by Seo4U.link

Keywords: iron oxide, oxide semiconductors, particle geometry, magnetic measurements.

ABSTRACT. Iron oxide (Fe2O3), Manganese oxide (MnO2) and Nickel oxide (NiO) nanopowder samples were prepared using mechanical grinding method and subjected to their structural and magnetic properties. Microstructures, crystallite size of the nanoparticles were studied using X-ray diffractometer (XRD). Magnetic measurements were carried out using vibrating sample magnetometer low temperature (100 K). From the magnetic studies, it was found that the magnetic moment increased with increase of applied field in iron oxide and saturation was not observed even at high magnetic fields. The magnetic studies of NiO revealed ferromagnetic behaviour whereas MnO2 undergoes paramagnetic behaviour.

Introduction. In recent years dilute magnetic oxide semiconductors are finding much interest due to their important properties such as optical transmittance, electrical conductivity and ferromagnetism. Due to these reasons much focus is being put on wide band gap metal oxide semiconductors such as indium oxide, tin oxide, zinc oxide, titanium oxide, copper oxide etc. These oxide materials are so important because they possess high carrier density, wide bang gap, ease of preparation, low cost and high Curie temperature. Among the other oxides, α-Fe2O3 also one of the most important material as it finds in many potential applications. It can form four different polymorphs such as alpha, beta, gamma and epsilon [1]. If the Fe2O3 nanoparticles were prepared of the order of single domain, they exhibit interesting properties such as superparamagnetism and large coerciviy. These nanoparticles find potential applications such as gas sensors, catalyst, photovoltaics, high density magnetic storage devices, bio separation, magnetic resonance imaging agent etc.[2-5]. Moreover efforts were put for the synthesis of nanoparticles using different physical and chemical methods. The literature survey indicates that different synthesis methods such as sputtering, decomposition, hydrothermal, solvothermal, sol-gel and electrochemical processes [6-9] were applied for the synthesis of

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

nanoparticles. Here in order study the impurity free α-Fe2O3, simple mechanical milling method was applied for the preparation of α-Fe2O3 nanoparticles. Experimental. The commercially available α-Fe2O3 powder was procured from Sigma Aldrich (India). α-Fe2O3 nanoparticles were prepared by simple mechanical milling method. The powder was milled using Agate mortar and ground thoroughly for 16 hours using pestle. After that the samples were characterized for structural, optical and magnetic properties. X-ray diffraction (X-ray diffractometer, D8 Advance, BRUKER) patterns were used to study the structural aspects. The optical reflectance and absorbance spectra were recorded using UV-VIS spectrophotometer (JASCO-V-670) in the wavelength range of 200 nm to 2500 nm. The magnetic studies were performed upto 0.1T field at low temperature (100 K) using vibration sample magnetometer (VSM Lakeshore 7404). Results and discussion.

Fe2O3 (3 0 0)

(a)

(1 2 2) (2 1 4)

2000

(0 2 4)

(1 1 0)

(0 1 2)

2500

(1 1 3)

(1 0 4)

3000

(1 1 6) (0 1 8)

Structural properties. Fig. 1 shows the X-ray diffraction profile of the Fe2O3 nanoparticles. The diffraction peaks such as (0 1 2), (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (1 2 2), (2 1 4) and (3 0 0) were found in their respective diffraction angles. From this, the structure of the nanoparticles was found to be in rhombohedral structure. These are in good agreement with that of standard XRD pattern of α-Fe2O3 derived from the JCPDS Card No. 33-664 [10]. No other diffraction peaks related to either FeO or Fe3O4 were found in the profile indicating that the source material is pure from any kind of impurities. Fig. 1 (b) shows the X-ray diffraction patterns of the MnO2 nanopowder. As shown in Fig. 1 (b), the diffraction peaks such as (1 1 0), (3 1 0), (2 1 1), (3 0 1), (4 1 1) and (5 2 1) reflections were found at 12.8°, 28.8°, 37.5°, 42.0°, 50.0°, 60.3° can be respectively.

(b)

(3 1 2)

MnO2 (0 0 2)

(5 2 1)

(4 3 1)

(2 1 1)

1500

(3 0 1)

2000

(3 1 0)

2000

NiO

(6 2 2)

4000

6000

(4 0 0 )

1000

(2 2 2)

Intensity (arbitrary units)

1500

2 (degrees)

Fig. 1. X-ray diffraction profiles of NiO, MnO2 and Fe2O3 nanoparticles. These reflections clear indexed to a tetragonal structure of standard MnO2 having JCPDS data Card no. 44-0141. Here also no other phases such as MnO, Mn2O3, Mn3O4 and Mn were found in the profile. Fig. 1 (c) shows the XRD profile of nickel oxide nanopowder. From the diffraction peaks it was found that the nanoparticle were in face centred cubic structure without any other impurity phases MMSE Journal. Open Access www.mmse.xyz 202

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within the detection limit of X-ray diffractometer. The observed results are found in good agreement with the standard JCPDS data Card No. 65-2901. The crystallite size (G) of all the samples has been calculated by using the Debye-Scherer formula,

(1)

where k is particle geometry dependent constant (for spherical shape k ~1),  is the wavelength of used ( = 1.5406 Å),  is the full width-at-half maximum (FWHM) and  is the diffracted angle, respectively. The estimated average crystallite size of α-Fe2O3, MnO2 and NiO are found to be about 39 nm, 32 nm and 19 nm respectively. Optical properties. Fig. 2 shows the diffuse reflectance spectrum of α-Fe2O3 nanoparticles. From the optical reflectance data, the optical band gap of the nanoparticles was estimated. The optical bang gap (Eg) was obtained by plotting (αhυ)2 versus the photon energy (hυ) and by extrapolating the linear region (α = 0). The optical band gap was estimated using the Tauc equation

100

Fe2O3

Reflection (%)

0 500

1000

1500

2000

Wavelength (nm)

Fig. 2. Diffused reflectance spectrum of α-Fe2O3 nanoparticles.

ℎ =

Eg − ℎ

(3)

where hν is the photon energy, α is the absorption coefficient and n is either 1/2 for a direct transition or 2 for an indirect transition. The optical band gap of semiconductor can be estimated from the intercept of the extrapolated linear fit for the plotted experimental data of (αhν)n versus incident photon energy hν near the absorption edge. An optical band gap of 2.08 eV was observed for α-Fe2O3 nanoparticles. The observed optical band gap is inconsistent with that of published work [11]. Magnetic properties. Fig. 3 shows the magnetic hysteresis measurements for MnO2, NiO and αFe2O3 samples at 100 K. It can be seen that the magnetization increases almost linearly under an applied magnetic field for all three samples. The saturation in the magnetization could not be observed even under the high magnetic field of 0.1T for α-Fe2O3. This observation is similar to the earlier study[12]. The ferromagnetism is observed in NiO nanoparticles unlike bulk NiO at low temperature MMSE Journal. Open Access www.mmse.xyz 203

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due to surface magnetization effect occurring at nanoscale. The MnO2 nanoparticles show paramagnetism at low temperature. Magnetic properties of similar oxides were studied and found that they exhibit diamagnetism in nature whereas on doping ferromagnetism was observed at 100 K [1315].

1.5

MnO2 Magnetization (emu/g)

1.0

NiO -Fe2O3

0.5 0.0 -0.5 -1.0 -1.5 -10.0k

-5.0k

0.0

5.0k

10.0k

Applied Field (Oe)

Fig. 3. M-H loop of MnO2, NiO and α- Fe2O3 nanoparticles. Summary. Powder samples of α-Fe2O3, MnO2 and NiO has been reduced to nanosize by mechanical grinding. They are then subjected to structural, optical and magnetic studies. The structural studies confirm the single phase formation of all the samples. The optical properties of α-Fe2O3 have been studied confirming the previous reports. The magnetic property of α-Fe2O3, MnO2 and NiO samples shows their inability to reach saturation magnetization at low temperature even on applying high field. The α-Fe2O3 and NiO nanoparticles showed ferromagnetism with maximum magnetization values as 0.198 emu/g and 1.507 emu/g respectively at 100 K. The MnO2 nanoparticles showed paramagnetic behaviour at 100 K. References [1] M.A. Chougule, S. Sen, V.B. Patil, Facile and efficient route for preparation of polypyrrole-ZnO nanocomposites: Microstructural, optical and charge transport properties, Journal of Applied Polymer Science, 125 (2012) E541-E547, DOI : 10.1002/app.36475. [2] E. Katz, I. Willner, A quinone-functionalized electrode in conjunction with hydrophobic magnetic nanoparticles acts as a "Write-Read-Erase" information storage system, Chemical Communications, (2005) 5641-5643, DOI : 10.1039/B511787A. [3] Y.-X.J. Wang, S.M. Hussain, G.P. Krestin, Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging, European Radiology, 11 (2001) 2319-2331, DOI : 10.1007/s003300100908. [4] S. Yan, D. Zhang, N. Gu, J. Zheng, A. Ding, Z. Wang, B. Xing, M. Ma, Y. Zhang, Therapeutic Effect of Fe2O3 Nanoparticles Combined with Magnetic Fluid Hyperthermia on Cultured Liver Cancer Cells and Xenograft Liver Cancers, Journal of Nanoscience and Nanotechnology, 5 (2005) 1185-1192, DOI : 10.1166/jnn.2005.219. [5] M. Zahn, Magnetic Fluid and Nanoparticle Applications to Nanotechnology, Journal of MMSE Journal. Open Access www.mmse.xyz 204

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Cite the paper B. Balaraju, M. Kuppan, S. Harinath Babu, S. Kaleemulla, N. Madhusudhana Rao, C. Krishnamoorthi, Girish M. Joshi, G. Venugopal Rao, K. Subbaravamma, I. Omkaram, D. Sreekantha Reddy (2017). Structural, Magnetic Properties of Wide Band Gap Oxide Semiconductors. Mechanics, Materials Science & Engineering, Vol 9. doi: 10.2412/mmse.95.56.253

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