Thin Solid Films 519 (2011) 8243–8246

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Thin Solid Films

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Room temperature ferromagnetism in Ni doped In2O3 nanoparticles

Ram Prakash a,⁎,1, Shalendra Kumar b, Faheem Ahmed b, Chan Gyu Lee b, Jung Il Song a

a Department of Mechanical Engineering, Changwon National University, #9 sarim-dong, Changwon-641-773, Republic of Koreab School of Nano and Advanced Materials Engineering, Changwon National University, #9 sarim-dong, Changwon-641-773, Republic of Korea

⁎ Corresponding author.E-mail addresses: rpgiuc@gmail.com (R. Prakash), jis

1 Present address: School of Physics, Shri Mata Vaish320, India.

0040-6090/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.tsf.2011.03.105

a b s t r a c t

a r t i c l e i n f o

Available online 6 April 2011

Keywords:In2O3

NanoparticlesXRDDiluted magnetic semiconductor

In the present work, Ni doped In2O3 nanoparticles were prepared using simple co-precipitation method. Fromthe x-ray diffraction analysis it is observed that all samples exhibit single phase polycrystalline nature. All thediffraction lines correspond to the bixbyite type cubic structure. A UV visible analysis reveals that optical bandgap decreases from 4.63 to 3.84 eV with Ni doping. DC magnetization measurements reveal that Ni dopedIn2O3 nanoparticles exhibit room temperature ferromagnetism.

ong@chanwon.ac.kr (J.I. Song).no Devi University, Katra-182

l rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Diluted magnetic semiconductor (DMS) obtained by introducingtransition metal (TM) into conventional semiconductors, have attractedmuch interest in potential spintronic applications due to its novelmagnetic, magneto-optical and magneto electrical properties [1]. Theprediction of room temperature (RT) ferromagnetism in Mn-doped ZnOand GaN by Dietl et al. [2] has triggered extensive studies on oxide-baseddiluted magnetic semiconductors (DMSs). Recently various transitionelements doped oxide semiconductor such as ZnO, TiO2, SnO2, MoO2 andIn2O3, have been studied extensively [3–12]. Indium oxide (In2O3) atransparent and wide band gap (3.75 eV) oxide, has a wide variety oftechnological applications, including flat-panel displays and gas sensors,due to a remarkable combination of optical transparency and electricalconductivity and/or dopability combined with a high work function.Indium oxide can exhibit considerable non-stoichiometry, and showsextremely good n-type dopability. The functional properties in theseoxides are, to a large extent, controlled by the presence of native pointdefects and impurities. The doping mechanism in In2O3 is considerablymore complex than thesimplepictureof everyoxygenvacancyproducingtwo free electrons. Oxygen-deficient In2O3 is highly compensated with aratio of the concentrationsof free carriers todonor defects of about 1:5. RTferromagnetism can be achieved by doping or co-doping of 3d transitionmetal (TM) impurities into In2O3,which is attractive due to its integrationof optical, electronic and magnetic properties into one single material.Various articles report the ferromagnetism in TM doped In2O3 [8–12].Chandradass et al. [8] had reported RTMF in Fe doped In2O3 nanoparticlespreparedbycoprecipitation.G. Peleckis [9], had reportedFM inMndoped

In2O3 below 46 K. Li et al. [10] had observed room-temperatureferromagnetism in Fe and Ni-co-doped In2O3 samples. In another study,Hong et al. [11] had reported RTFM in Co doped In2O3 thin films. Subiaset al. [12] had reported local structure of Co doped In2O3 using x-rayabsorption spectroscopy. In the present paper, we have prepared Nidoped In2O3 nanoparticles and studied their structural and magneticproperties. These nanoparticles are crystalline and single phase and showroom temperature ferromagnetism.

2. Experimental detail

Ni doped In2O3 nanoparticles of composition (In1− xNix)2O3

(0≤×≥0.10) were prepared by a simple co-precipitation method.The starting materials of In(NO3)3·9H2O, Ni(NO3)2·9H2O and NH4OHwere of analytical grade. Different mole ratios of In(NO3)3·9H2O andNi(NO3)2·9H2O were added into 20 ml distilled water: the solutionwas then under magnetic stirring at room temperature for 0.5 h.Ammonium hydroxide was slowly dripped into the former solutionunder stirring until the pH=9 was reached. The obtained whiteprecipitate was washed by ethanol, dried at 80 °C for 24 h, andtransferred to alumina crucible, calcined at 400 °C for 5 h in airatmosphere. The thermal decomposition behavior of the washed anddried gel was studied by TG–DTA analysis (STA 1500). These thermalstudies were used to get the calcination temperature for thesenanoparticles. The crystalline quality and phase of the sample wascharacterized by X-ray diffraction (XRD) (Philips X'Pert MPD3040diffractometer) using Cu Kα radiation in the 2θ range 10–90°. Thevoltage and the current settings were 40 kV and 30 mA, respectively.The samples were continuously scanned with a step size of 0.02° (2θ)at a count time of 1 s per step. The particle size of the calcinatedpowder particles was observed using scanning electron microscope(TESCAN, Mira II LMH) at an accelerating voltage of 30 kV with anattached energy dispersed X-ray spectrometer (EDS). Raman spec-troscopy measurements were done using Micro Raman spectrometer

Fig. 1. X-ray diffraction patterns of (In1−xNix)2O3 (x=0.0, 0.01, 0.03, 0.05, 0.07 and0.10) nanoparticles . Inset shows the plot of lattice parameters with x values (Nicontent).

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(Model-NRS-3100 from JASCO, Japan) with laser wavelength of532 nm. The optical absorbance spectra were measured using a UV–VIS spectrophotometer (Aglilent 8453) at room temperature in thewavelength range of 200 nm to 800 nm. The magnetic properties ofthe products were characterized by a PPMS-physical propertymeasurement system (Quantum Design, Inc.).

Fig. 2. FE–SEM images of (In1−xNix)2O3 with x=(a) 0.0, (b) 0

3. Results and discussion

Fig. 1 shows the XRD pattern of Ni doped In2O3 nanoparticles offormula (In1−xNix)2O3 with x values x=0, 0.1, 0.03, 0.05, 0.07 and0.10. The XRD pattern of undoped In2O3 is single phase and can beindexed as cubic structure with JCPDS No. 71-2195. The differentpeaks are marked with corresponding reflection planes in the pattern.Most of the intense peaks from JCPDS data are present in the samples.XRD patterns of all Ni doped samples have single phase nature, similarto undoped sample. The XRD patterns of doped samples are slightlyshifted to lower 2θ values indicating increase in inter-planer spacingof the corresponding planes resulting in an increase in latticeparameter. Since (222) reflection is the highest intensity peak for allthe samples, therefore, we chose this peak for calculation ofcrystalline size of nanoparticles. We calculated crystallite size (D) ofthe nanoparticles using the Debye–Scherrer formula [13] given by

D = 0:94 × λ = B cos θð Þ

where λ is the wavelength of the x-ray source and B2=Γ2−b2 inwhich Γ is the full width at half maximum (FWHM) of an individualpeak at 2θ (where θ is the Bragg angle) and b is instrumentalbroadening.

The lattice parameter is increasing with increasing Ni dopingconcentration. Inset in Fig. 1 shows the plot of lattice parameter withNi content in the nanoparticles. The lattice parameter for undopedsample is 10.123 Å which increased to 10.132 Å for 10 at.% Ni dopedsample. The increase in lattice parameter with Ni doping indicates

.01, (c) 0.03, (d) 0.05, (e) 0.07 and (f) 0.10 nanoparticles.

Fig. 3. Raman spectra of (In1−xNix)2O3 (x=0.0, 0.01, 0.03, 0.05, 0.07 and 0.10)nanoparticles. Fig. 5. Magnetization hysteresis (M-H) curve of (In1−xNix)2O3 (x=0.0, 0.01, 0.05 and

0.07) nanoparticles measured at room temperature.

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inclusion of Ni in In2O3 crystal. The crystalline size for undopedsample is 12 nm and it increased to 14 nm for 10% Ni doped sampleindicating that particle size does not change much with Ni doping upto 10 at.%.

After confirming that our samples are single phase, we haveperformed FE–SEM measurements to get the shape and size of thenanoparticles. From the SEM micrographs it clear that particles arespherical in shape and their diameter is increasing with Ni dopingwhich is in accordance with crystalline size variation obtained fromXRD data. The variation of particle size can be seen from themicrographs as shown in Fig. 2. The conditions of measurementsuch as magnification and operating voltage were 200kX and 30kV,respectively for all samples. The particle sizes estimated from SEManalysis are in well agreement with that calculated from XRD data.

Fig. 3 shows Raman spectra of Ni doped In2O3 nanoparticles. TheseRaman spectra were recorded in the range 100–1150 cm−1 at roomtemperature. The In2O3 belongs to cubic C-type rare earth oxidestructure and for this type of structure the factor group analysispredicts 4 Ag (Raman), 4 Eg (Raman)+14 Tg (Raman)+5 Au

(inactive)+5 Au (inactive)+14 Tu (Infra-red) modes [14]. Donget al. [15] have reported Raman peaks at wave numbers 126, 300, 360489 and 622 cm−1 for In2O3 nanowires. In the present case, Ramanmodes are observed at 180, 142, 473, 629,794, and 1077 cm−1 for allsamples undoped and Ni doped In2O3 nanoparticles. The positions ofRamanmodes do not changemuchwith Ni doping, indicating that thestructure of the host matrix remains the same up to 10 at.% Ni dopingin In2O3 host matrix. These observed positions are characteristic ofstandard Raman spectra for In2O3 and these observed values of Ramanmodes are also in agreement with the previously reported [14–16]values.

Fig. 4. UV Visible spectra of (In1− xNix)2O3 (x=0.0, 0.01, 0.07 and 0.10) nanoparticles.

Optical properties of Ni doped In2O3 nanoparticles were charac-terized using a UV–VIS spectrophotometer. The absorption coefficientα can be calculated from the relation:

α = 2:303�a=t

where a is the absorbance and t is the thickness of the cuvette. Theoptical band gap of the nanoparticles was determined by applying theTauc relationship [17] given by:

αhν = A hν−Eg� �n

where A is a constant, h is Planck's constant, ν is the photon frequency,Eg is the optical band gap and n = 1

2 for direct band gap semiconduc-tor. An extrapolation of the linear region of a plot of (αhν)2 on the Y-axis versus photon energy (hν) on the X-axis gives the value of theoptical band gap (Eg). The plots of (αhν)2 and hν are shown in Fig. 4for Ni doped In2O3 nanoparticles. The calculated value of optical bandgap for undoped nanoparticles is 4.63 eV which decreases with Nidoping. The calculated values of band gap for 1 and 7 at.% Ni dopedsamples are found to be 4.36, and 3.84 eV respectively. Thesecalculated values of band gap are higher than bulk In2O3 value(3.7 eV) indicating blue shift with bulk reported values. These resultsare in good agreementwith the reported values for nanoparticles [18].

To study the magnetic properties of these nanoparticles, we havemeasured magnetic hysteresis at room temperature using PPMSsystem. The magnetic hysteresis is shown in Fig. 5 for (In1−xNix)2O3

(x=0, 0.1, 0.03, 0.05, and 0.07) nanoparticles. Inset in Fig. 5 shows theexpanded view of hysteresis loops. All the Ni doped samples showferromagnetic hysteresis, indicating room temperature ferromagne-tism in Ni doped samples while the undoped sample also shows weakferromagnetism. The saturation magnetization increases from0.01 emu/g to 0.032 emu/g with increase in Ni doping from 1 at.% to7 at.% in the Ni doped In2O3 nanoparticles. The increase in magneti-zation values with Ni doping indicates that the observed ferromag-netism is due to Ni doping. Further study is in progress to get insight ofthe origin of ferromagnetism in these nanoparticles.

5. Conclusion

In conclusion, we have prepared Ni doped In2O3 nanoparticlesusing the co-precipitation method. The prepared nanoparticles werecharacterized by the x-ray diffraction, scanning electron microscopy,Raman spectroscopy, UV–visible spectroscopy and dc magnetizationhysteresis loop measurements. XRD results reveal that all samplesexhibit single phase polycrystalline nature. XRD patterns correspondto bixbyite type cubic structure of In2O3. Optical band gap decreases

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with Ni doping. Ni doped In2O3 nanoparticles exhibit ferromagnetichysteresis loop at room temperature.

Acknowledgments

This work is supported by research fund of Brain Korea 21 (BK21)Project Crops of second phase.

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