This work is aimed at synthesizing and characterizing transition metals (Mn, Fe and Ni) doped ZnO nanostructures. The samples have been prepared by chemical co-precipitation method. The samples have been divided and one half has been coated SiO2. X-Ray diffraction indicated the formation of single phase ZnO. Optical and photoluminescence studies have been carried out using UV-Vis spectroscopy and Photoluminescence spectroscopy respectively. Magnetic responses of the samples have been studied using SQUID. The structural studies revealed that sample is having wurzite structure at room temperature. Magnetization results shows the ferromagnetism in 2  Fe doped, 5  Ni doped and 2  Mn doped ZnO.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3102

Bandyopadhyay, V.

Bhushan, K.

Mukherjee, S.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 5 No 2, 02030(5pp) (2013) Том 5 № 2, 02030(5cc) (2013) 
 
 
2077-6772/2013/5(2)02030(5) 02030-1  2013 Sumy State University 
Evidence of Itinerant Ferromagnetism in Transition Metal Doped ZnO Nanostructures 
 
V. Bandyopadhyay, K. Bhushan, S. Mukherjee* 
 
Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi – 835215 Jharkhand, India 
 
(Received 15 February 2013; published online 04 May 2013) 
 
This work is aimed at synthesizing and characterizing transition metals (Mn, Fe and Ni) doped ZnO 
nanostructures. The samples have been prepared by chemical co-precipitation method. The samples have 
been divided and one half has been coated SiO2. X-Ray diffraction indicated the formation of single phase 
ZnO. Optical and photoluminescence studies have been carried out using UV-Vis spectroscopy and Photo-
luminescence spectroscopy respectively. Magnetic responses of the samples have been studied using 
SQUID. The structural studies revealed that sample is having wurzite structure at room temperature. 
Magnetization results shows the ferromagnetism in 2  Fe doped, 5  Ni doped and 2  Mn doped ZnO.  
 
Keywords: ZnO, Dilute magnetic semiconductors, Co-precipitation, Ferromagnetism, Superconductivity. 
 
 PACS number: 75.50.Pp 
 
 
                                                                
* samrat.udc@gmail.com 
1. INTRODUCTION 
 
Diluted magnetic semiconductors (DMS) have re-
cently attracted huge research attention because of 
their potential application for spintronics devices. In 
DMS materials, transition or rare earth metal ions are 
substituted onto cation sites and are coupled with free 
carriers to yield ferromagnetism via indirect interac-
tions. ZnO based DMS is particularly interesting since 
it shows interesting spintronics property at room tem-
peratures. There has been a lot of interest in doping 
ZnO with 3d transition metal ions, since the prediction 
made by Dietl et al. [1] that Mn-doped ZnO would be 
ferromagnetic at room temperature. Magnetic impuri-
ties, like transition metals, can make the semiconductor 
half-metallic: the majority spin bands are metallic and 
the minority spin bands are semiconducting; as a result, 
the compound presents a fully (100 ) spin polarized 
density of states (DOS) at the Fermi energy, and this 
property is used in electronic industries to build 
spintronics devices [2]. 
ZnO is a of II-VI compound semiconductor of the pe-
riodic table whose ionicity resides at borderline be-
tween covalent and ionic semiconductor [3]. The elec-
tronegative difference between zinc and oxygen pro-
duce a high degree of ionicity in its bond. Considering 
that the n-type ZnO is easily available and the intrinsic 
defects such as the O-vacancies and Zn- interstitial 
work as donor it can be concluded that the (Zn, Fe)O, 
(Zn, Co)O and (Zn, Ni)O are promising candidates for 
achieving high-TC ferromagnetism. 
 
2. EXPERIMENTAL 
 
Transition metal doped ZnO nanostructures were 
synthesized by chemical co-precipitation method [4-7]. 
We have prepared three series of samples of generic 
formula FexZn(1 – x)O, NixZn(1 – x)O and last one of 
MnxZn(1 – x)O where x is 0.02 and 0.05. In each case, one 
sample is coated with SiO2 and another is left  
uncoated. For the synthesis of all the samples, Zinc 
nitrate hexahydrate (N2O6Zn.6H2O), Iron(III)nitrate 
nonahydrate(FeN3O9.9H2O), Nickel(II)nitrate hexahy-
drate(N2NiO6.6H2O), Manganese(II)Chloride (MnCl2) 
and sodium Hydroxide (NaOH) were used which are 
procured from Sigma Aldrich. Tetra ethyl orthosilicate 
(TEOS) was used for coating the nanocrystals formed 
by solution method. For synthesis of the first series of 
generic formula FexZn(1 – x)O, calculated weights of salts 
of Zn for forming ZnO host and as well as Fe as do-
pants were dissolved in methanol at room temperature 
to produce a solution with a total concentration of met-
al ions of 0.1 M. A solution of NaOH in methanol was 
used as the precipitating agent and was added drop-
wise to the solution in a temperature of 80 °C. This 
thermal condition also favors the reduction of the metal 
ions to metal clusters, leading to a composite material 
formed mainly by doped zinc oxide decorated with met-
al clusters. These clusters appear to be the main spe-
cies responsible for the ferromagnetism of the Fe doped 
zinc oxide. Thus, by this process, the ferromagnetism is 
a result of extrinsic character rather than an intrinsic 
one [8]. To achieve adequate precipitation, the alkali 
solution was added until the pH of the solution with 
metal ions reach 10.  
When reaction was completed, the precipitate was 
separated from the supernatant by centrifuge machine 
operating at a speed of 1500 rpm, and washed several 
times with ethanol and then dried at room tempera-
ture. The precipitated part is then divided into two 
parts; one part is coated using TEOS (tetra ethyl ortho-
silicate) and dried at the room temperature. For the 
second series of generic formula NixZn(1 – x)O, salts of Zn 
and Ni were used and similarly for the third one of 
MnxZn(1 – x)O with Zn and Mn. The remaining steps 
were same as that of the first series of samples. 
 
3. RESULTS AND DISCUSSION 
 
3.1 X-Ray Diffraction 
 
Structural analysis of transition metal doped ZnO 
nanoparticles was performed in an X ray diffractometer 
(XRD) using CoKα (   1.788 nm). XRD patterns of all 
the samples of the series of doped ZnO nanocrystals 
were shown in Fig. 1a, b and c. The sharp intense 
peaks originated from (100), (002), (101), (102), (110), 
(103), (200) in all the samples confirms the good crys-
 V. BANDYOPADHYAY, K. BHUSHAN, S. MUKHERJEE J. NANO- ELECTRON. PHYS. 5, 02030 (2013) 
 
 
02030-2 
talline nature of würtzite-type ZnO [9]. The average 
crystallite sizes (Dav) were estimated by using the De-
bye-Scherrer equation [10] in our experiment. 
 
 
1 2
0.9
cos
avD   
 
In the above equation,  represents the wavelength 
of the X-ray radiation, 1/2 the full width at half maxi-
mum of the diffraction peak (in radians) and θ the max-
imum scatter angle. 
 
 
 
(a) 
 
 
 
(b) 
 
Fig. 1 – XRD Representative patterns of transition metal 
doped ZnO Nanostructures: Series of generic formula  
FexZn(1 – x)O (a), Series of generic formula MnxZn(1 – x)O (b). 
 
Table 1 – Average particle size estimated from the diffraction 
spectrum in Fig. 1 by using FWHM 
 
Sample 
Name 
Type of 
Particle 
2θ 
FWHM 
( ) 
in 
radians 
Average 
size of 
the particle 
(nm 
approx) 
Fe0.02Zn0.98O Coated 38.25 0.021 24 
Uncoated 38.46 0.025 21 
Fe0.05Zn0.95O Coated 40.00 0.022 24 
Uncoated 38.46 0.021 25 
Ni0.02Zn0.98O Coated 37.36 0.013 36 
Uncoated 38.64 0.021 25 
Ni0.05Zn0.95O Coated 37.33 0.005 97 
Uncoated 38.89 0.019 28 
Mn0.02Zn0.98O Coated 37.39 0.019 27 
Uncoated 37.36 0.009 51 
Mn0.05Zn0.95O Coated 37.36 0.011 65 
Uncoated 37.36 0.016 46 
 
We use the (101) peak in the XRD patterns to calcu-
late the average crystallite size. From Table 1 we can 
clearly observe that the particle size of the coated sam-
ple is larger as compared to the uncoated samples, this 
is due to the coating of amorphous silicon dioxide 
around the particles resulting in increased size. The 
absence of any extra peak in the XRD of Mn and Ni 
doped ZnO suggests that the actual incorporation of 
dopant species into the ZnO structure. A higher base-
line is observed in case of all coated samples, this can 
be explained as the formation of amorphous silicon di-
oxide due to coating. 
 
3.2 UV-Visible Spectroscopy 
 
Optical analysis of the doped ZnO nanoparticles was 
performed by an Ultraviolet-visible spectroscopy in the 
region from 200 nm to 800 nm at room temperature. 
Fig. 2a, b and c shows spectrum of absorption versus 
photon energy of the samples. 
The estimated band gap value of ZnO is approxi-
mately 3.3 eV for the nanoparticle [11], and one can ob-
serve that the band gap changes due to doping the tran-
sition metal in ZnO. The systematic shifts with doping 
levels suggest that it is due to the introduction of dopant 
ions, rather than size effects which brings these changes. 
This is further corroborated due to the fact that the sizes 
of the nanoparticles are well above the confinement re-
gion. A number of previous experimental and theoretical 
investigations have suggested that size effects have little 
or no influence on the band structure of ZnO nanocrys-
tals with diameters greater than 7.0 nm [12]. In our ex-
periment here the XRD results is showing the size 
greater than 7.0 nm therefore we have to drop that rea-
son of size for the increment of the band gap rather is 
due to the doping of transition metal. 
The bandgap was calculated by differentiating the as 
obtained graphs and the higher wavelength side was con-
sidered. The was done because the first change in slope 
indicates the onset of the valence to conduction band edge 
transition. 
Table 2 enlists the bandgap of all the samples of tran-
sition metal doped ZnO nanostructures. 
 
Table 2 – Estimated band gaps of the samples 
 
 
3.3 PL Spectroscopy 
 
Photoluminescence analysis of the doped ZnO nanostruc-
tures were performed at room temperature from the dis-
persed particles in methanol. Xenon lamp source at an 
excitation wavelength of 280 nm is used for the analysis. 
Photoluminescence and absorption in semiconductors 
Sample 
Name 
Type of 
Particle 
Peak at Wave-
length (nm) 
Bandgap 
(eV) 
Fe0.02Zn0.98O Coated 372 3.33 
Uncoated 373 3.32 
Fe0.05Zn0.95O Coated 369 3.36 
Uncoated 373 3.32 
Ni0.02Zn0.98O Coated 376 3.30 
Uncoated 379 3.27 
Ni0.05Zn0.95O Coated 351 3.53 
Uncoated 376 3.29 
Mn0.02Zn0.98O Coated 369 3.36 
Uncoated 371 3.34 
Mn0.05Zn0.95O Coated 342 3.63 
Uncoated 364 3.41 
 EVIDENCE OF ITINERANT FERROMAGNETISM IN… J. NANO- ELECTRON. PHYS. 5, 02030 (2013) 
 
 
02030-3 
 
(a) 
 
 
(b) 
 
 
 
(c) 
 
Fig. 2 – UV-Vis patterns of transition metal doped ZnO 
Nanostructures: Series of generic formula FexZn(1 – x)O (a), Series 
of generic formula NixZn(1 – x)O (b), Series of generic formula 
MnxZn(1 – x)O (c) 
 
strongly relies on the assumption that the recombination 
times are much larger than the intraband relaxation 
times. 
The energy of a donor-acceptor pair in bulk ZnO can 
be calculated as: 
 
 EDAP  Eg – EDBindEABind + e2 / 4 0RDA (13) 
 
where Eg is the band gap (distance between conduction 
and valence bands), which is 3.437 eV at 2 K, EDBind is the 
binding energy of donor (energy below the bottom of con-
duction band), EABind is the binding energy of an acceptor 
 
 
(a) 
 
 
 
(b) 
 
 
 
(c) 
 
Fig. 3 – PL Spectra of transition metal doped ZnO Nanostruc-
tures: Series of generic formula FexZn(1 – x)O (a), Series of generic 
formula NixZn(1 – x)O (b), Series of generic formula MnxZn(1 – x)O (c) 
 
(energy above the top of valence band), 0 is the permittivi-
ty of free space, e is the electron charge, є is the dielectric 
constant and RDA is the donor-acceptor pair separation. 
The photoluminescence spectra of the three sets of sam-
ples are shown in Fig. 3a, b and c. 
Considering the spectral information of all the sam-
ples, strong peaks ranging from 370 nm to 391 nm were 
observed. A typical ZnO UV-exitonic emission band 
around 380 nm is observed, which is the characteristics of 
band edge emission. On being exposed to 280 nm radia-
tion the prepared samples emits visible blue line. This 
visible emission is also evident from the photolumines-
cence graph as shown in Fig. 3. 
 
 V. BANDYOPADHYAY, K. BHUSHAN, S. MUKHERJEE J. NANO- ELECTRON. PHYS. 5, 02030 (2013) 
 
 
02030-4 
Table 3 – Emission Wavelength by PL Emission Spectra 
 
Sample 
Name 
Type of 
Particle 
Peak at 
Wavelength (nm) 
Fe0.02Zn0.98O Coated 383 
Uncoated 382 
Fe0.05Zn0.95O Coated 360 
Uncoated 382 
Ni0.02Zn0.98O Coated 370 
Uncoated 381 
Ni0.05Zn0.95O Coated 380 
Uncoated 391 
Mn0.02Zn0.98O Coated 385 
Uncoated 382 
Mn0.05Zn0.95O Coated 378 
Uncoated 372 
 
3.4 Magnetization Measurements 
 
The magnetization responses of all the uncoated sam-
ples were studied in a SQUID (Quantum Design). The M-
H responses of the samples are shown in Fig. 4a, b and c. 
The sample doped with Mn shows the highest 
magnetic response whereas for Fe and Ni the response 
is extremely weak. The coercivity obtained for the 
samples and varies from 114 Oe to 189 Oe which is 
definitely more than other reports [15]. The ferromag-
netic nature cannot be a consequence of metal-metal 
interaction because the medium in which the samples 
have been prepared do not have any reducing proper-
ties. The ferromagnetic behaviour observed in the 
samples is probably due to competition between the 
double-exchange interaction and the antiferromagnetic 
 
     
(a) 
 
     
(b) 
 
 
 
(c) 
 
Fig. 4 – M-H curve at room temperature of Fe doped ZnO nanostructures (a), Ni doped ZnO nanostructures (b), Mn doped ZnO 
nanostructures 
 EVIDENCE OF ITINERANT FERROMAGNETISM IN… J. NANO- ELECTRON. PHYS. 5, 02030 (2013) 
 
 
02030-5 
superexchange interaction in the material. The low mag-
netization and coercivity values measured for our samples 
are standard properties of nanocrystalline dilute magnetic 
semiconductors. Radovanovic [16] suggested the for-
mation of dense aggregates of Ni-doped ZnO nanocrystals 
as responsible for observed ferromagnetism. 
Fig. 5 shows the ZFC and FC curves for the 5 % Fe 
doped ZnO nanocrystals. The observed monotonic fall 
suggests a thermodynamically equilibrium state reminis-
cent of Curie’s law. A small hump at about 60 K may be 
attributed to presence of ferromagnetic re-entrant behav-
iour. 
 
 
 
Fig. 5 – Zero field cooled (ZFC) and field cooled (FC) magneti-
zation as a function of temperature for 5 % Fe doped ZnO 
nanostructures 
4. CONCLUSION 
 
The present work was focused on synthesis of transi-
tion metal doped ZnO nano crystals in methanol solution 
at room temperature and their structural, optical and 
magnetic characterization. Mn, Fe and Ni doped ZnO, 
doped in composition x  0.02 and 0.05 where synthe-
sized by co-precipitation low entropy method. The crystal 
structure, magnetic properties and optical properties 
have been investigated by X-ray diffraction (XRD), 
SQUID, UV-Visible and PL spectroscopy respectively. 
The X-ray diffraction showed that the prepared sam-
ples are single phase with the ZnO like wurtzite struc-
ture. No secondary phase was found in XRD spectrum. 
The blue shift in the band gap of transition metal ion 
doped ZnO was observed in PL emission spectra. A band 
gap between 3.27 eV to 3.67 eV was calculated for differ-
ent composition and different transition metal doping by 
UV Visible spectroscopy. The enhancement of the bang 
gap energy was attributed to the incorporation of dopant 
ion into the ZnO host structure. 
The magnetic responses the room temperature fer-
romagnetic properties in 2 % Fe doped, 5 % Ni doped 
and 2 % Mn doped ZnO. Our analysis suggests that this 
noticeable ferromagnetism can be attributed to actual 
incorporation of magnetic ions into the diamagnetic ZnO 
host structure. 
 
ACKNOWLEDGEMENTS 
 
One of the authors, SM is grateful to AICTE, Govt. 
of India for financial support for the work.
 
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Evidence of Itinerant Ferromagnetism in Transition Metal Doped ZnO Nanostructures

Electronic Sumy State University Institutional Repository

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ Vol. 5 No 2, 02030(5pp) (2013) Том 5 № 2, 02030(5cc) (2013)   2077-6772/2013/5(2)02030(5) 02030-1  2013 Sumy State University Evidence of Itinerant Ferromagnetism in Transition Metal Doped ZnO Nanostructures  V. Bandyopadhyay, K. Bhushan, S. Mukherjee*  Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi – 835215 Jharkhand, India  (Received 15 February 2013; published online 04 May 2013)  This work is aimed at synthesizing and characterizing transition metals (Mn, Fe and Ni) doped ZnO nanostructures. The samples have been prepared by chemical co-precipitation method. The samples have been divided and one half has been coated SiO2. X-Ray diffraction indicated the formation of single phase ZnO. Optical and photoluminescence studies have been carried out using UV-Vis spectroscopy and Photo-luminescence spectroscopy respectively. Magnetic responses of the samples have been studied using SQUID. The structural studies revealed that sample is having wurzite structure at room temperature. Magnetization results shows the ferromagnetism in 2  Fe doped, 5  Ni doped and 2  Mn doped ZnO.   Keywords: ZnO, Dilute magnetic semiconductors, Co-precipitation, Ferromagnetism, Superconductivity.   PACS number: 75.50.Pp                                                                   * samrat.udc@gmail.com 1. INTRODUCTION  Diluted magnetic semiconductors (DMS) have re-cently attracted huge research attention because of their potential application for spintronics devices. In DMS materials, transition or rare earth metal ions are substituted onto cation sites and are coupled with free carriers to yield ferromagnetism via indirect interac-tions. ZnO based DMS is particularly interesting since it shows interesting spintronics property at room tem-peratures. There has been a lot of interest in doping ZnO with 3d transition metal ions, since the prediction made by Dietl et al. [1] that Mn-doped ZnO would be ferromagnetic at room temperature. Magnetic impuri-ties, like transition metals, can make the semiconductor half-metallic: the majority spin bands are metallic and the minority spin bands are semiconducting; as a result, the compound presents a fully (100 ) spin polarized density of states (DOS) at the Fermi energy, and this property is used in electronic industries to build spintronics devices [2]. ZnO is a of II-VI compound semiconductor of the pe-riodic table whose ionicity resides at borderline be-tween covalent and ionic semiconductor [3]. The elec-tronegative difference between zinc and oxygen pro-duce a high degree of ionicity in its bond. Considering that the n-type ZnO is easily available and the intrinsic defects such as the O-vacancies and Zn- interstitial work as donor it can be concluded that the (Zn, Fe)O, (Zn, Co)O and (Zn, Ni)O are promising candidates for achieving high-TC ferromagnetism.  2. EXPERIMENTAL  Transition metal doped ZnO nanostructures were synthesized by chemical co-precipitation method [4-7]. We have prepared three series of samples of generic formula FexZn(1 – x)O, NixZn(1 – x)O and last one of MnxZn(1 – x)O where x is 0.02 and 0.05. In each case, one sample is coated with SiO2 and another is left  uncoated. For the synthesis of all the samples, Zinc nitrate hexahydrate (N2O6Zn.6H2O), Iron(III)nitrate nonahydrate(FeN3O9.9H2O), Nickel(II)nitrate hexahy-drate(N2NiO6.6H2O), Manganese(II)Chloride (MnCl2) and sodium Hydroxide (NaOH) were used which are procured from Sigma Aldrich. Tetra ethyl orthosilicate (TEOS) was used for coating the nanocrystals formed by solution method. For synthesis of the first series of generic formula FexZn(1 – x)O, calculated weights of salts of Zn for forming ZnO host and as well as Fe as do-pants were dissolved in methanol at room temperature to produce a solution with a total concentration of met-al ions of 0.1 M. A solution of NaOH in methanol was used as the precipitating agent and was added drop-wise to the solution in a temperature of 80 °C. This thermal condition also favors the reduction of the metal ions to metal clusters, leading to a composite material formed mainly by doped zinc oxide decorated with met-al clusters. These clusters appear to be the main spe-cies responsible for the ferromagnetism of the Fe doped zinc oxide. Thus, by this process, the ferromagnetism is a result of extrinsic character rather than an intrinsic one [8]. To achieve adequate precipitation, the alkali solution was added until the pH of the solution with metal ions reach 10.  When reaction was completed, the precipitate was separated from the supernatant by centrifuge machine operating at a speed of 1500 rpm, and washed several times with ethanol and then dried at room tempera-ture. The precipitated part is then divided into two parts; one part is coated using TEOS (tetra ethyl ortho-silicate) and dried at the room temperature. For the second series of generic formula NixZn(1 – x)O, salts of Zn and Ni were used and similarly for the third one of MnxZn(1 – x)O with Zn and Mn. The remaining steps were same as that of the first series of samples.  3. RESULTS AND DISCUSSION  3.1 X-Ray Diffraction  Structural analysis of transition metal doped ZnO nanoparticles was performed in an X ray diffractometer (XRD) using CoKα (   1.788 nm). XRD patterns of all the samples of the series of doped ZnO nanocrystals were shown in Fig. 1a, b and c. The sharp intense peaks originated from (100), (002), (101), (102), (110), (103), (200) in all the samples confirms the good crys- V. BANDYOPADHYAY, K. BHUSHAN, S. MUKHERJEE J. NANO- ELECTRON. PHYS. 5, 02030 (2013)   02030-2 talline nature of würtzite-type ZnO [9]. The average crystallite sizes (Dav) were estimated by using the De-bye-Scherrer equation [10] in our experiment.   1 20.9cosavD    In the above equation,  represents the wavelength of the X-ray radiation, 1/2 the full width at half maxi-mum of the diffraction peak (in radians) and θ the max-imum scatter angle.    (a)    (b)  Fig. 1 – XRD Representative patterns of transition metal doped ZnO Nanostructures: Series of generic formula  FexZn(1 – x)O (a), Series of generic formula MnxZn(1 – x)O (b).  Table 1 – Average particle size estimated from the diffraction spectrum in Fig. 1 by using FWHM  Sample Name Type of Particle 2θ FWHM ( ) in radians Average size of the particle (nm approx) Fe0.02Zn0.98O Coated 38.25 0.021 24 Uncoated 38.46 0.025 21 Fe0.05Zn0.95O Coated 40.00 0.022 24 Uncoated 38.46 0.021 25 Ni0.02Zn0.98O Coated 37.36 0.013 36 Uncoated 38.64 0.021 25 Ni0.05Zn0.95O Coated 37.33 0.005 97 Uncoated 38.89 0.019 28 Mn0.02Zn0.98O Coated 37.39 0.019 27 Uncoated 37.36 0.009 51 Mn0.05Zn0.95O Coated 37.36 0.011 65 Uncoated 37.36 0.016 46  We use the (101) peak in the XRD patterns to calcu-late the average crystallite size. From Table 1 we can clearly observe that the particle size of the coated sam-ple is larger as compared to the uncoated samples, this is due to the coating of amorphous silicon dioxide around the particles resulting in increased size. The absence of any extra peak in the XRD of Mn and Ni doped ZnO suggests that the actual incorporation of dopant species into the ZnO structure. A higher base-line is observed in case of all coated samples, this can be explained as the formation of amorphous silicon di-oxide due to coating.  3.2 UV-Visible Spectroscopy  Optical analysis of the doped ZnO nanoparticles was performed by an Ultraviolet-visible spectroscopy in the region from 200 nm to 800 nm at room temperature. Fig. 2a, b and c shows spectrum of absorption versus photon energy of the samples. The estimated band gap value of ZnO is approxi-mately 3.3 eV for the nanoparticle [11], and one can ob-serve that the band gap changes due to doping the tran-sition metal in ZnO. The systematic shifts with doping levels suggest that it is due to the introduction of dopant ions, rather than size effects which brings these changes. This is further corroborated due to the fact that the sizes of the nanoparticles are well above the confinement re-gion. A number of previous experimental and theoretical investigations have suggested that size effects have little or no influence on the band structure of ZnO nanocrys-tals with diameters greater than 7.0 nm [12]. In our ex-periment here the XRD results is showing the size greater than 7.0 nm therefore we have to drop that rea-son of size for the increment of the band gap rather is due to the doping of transition metal. The bandgap was calculated by differentiating the as obtained graphs and the higher wavelength side was con-sidered. The was done because the first change in slope indicates the onset of the valence to conduction band edge transition. Table 2 enlists the bandgap of all the samples of tran-sition metal doped ZnO nanostructures.  Table 2 – Estimated band gaps of the samples   3.3 PL Spectroscopy  Photoluminescence analysis of the doped ZnO nanostruc-tures were performed at room temperature from the dis-persed particles in methanol. Xenon lamp source at an excitation wavelength of 280 nm is used for the analysis. Photoluminescence and absorption in semiconductors Sample Name Type of Particle Peak at Wave-length (nm) Bandgap (eV) Fe0.02Zn0.98O Coated 372 3.33 Uncoated 373 3.32 Fe0.05Zn0.95O Coated 369 3.36 Uncoated 373 3.32 Ni0.02Zn0.98O Coated 376 3.30 Uncoated 379 3.27 Ni0.05Zn0.95O Coated 351 3.53 Uncoated 376 3.29 Mn0.02Zn0.98O Coated 369 3.36 Uncoated 371 3.34 Mn0.05Zn0.95O Coated 342 3.63 Uncoated 364 3.41  EVIDENCE OF ITINERANT FERROMAGNETISM IN… J. NANO- ELECTRON. PHYS. 5, 02030 (2013)   02030-3  (a)   (b)    (c)  Fig. 2 – UV-Vis patterns of transition metal doped ZnO Nanostructures: Series of generic formula FexZn(1 – x)O (a), Series of generic formula NixZn(1 – x)O (b), Series of generic formula MnxZn(1 – x)O (c)  strongly relies on the assumption that the recombination times are much larger than the intraband relaxation times. The energy of a donor-acceptor pair in bulk ZnO can be calculated as:   EDAP  Eg – EDBindEABind + e2 / 4 0RDA (13)  where Eg is the band gap (distance between conduction and valence bands), which is 3.437 eV at 2 K, EDBind is the binding energy of donor (energy below the bottom of con-duction band), EABind is the binding energy of an acceptor   (a)    (b)    (c)  Fig. 3 – PL Spectra of transition metal doped ZnO Nanostruc-tures: Series of generic formula FexZn(1 – x)O (a), Series of generic formula NixZn(1 – x)O (b), Series of generic formula MnxZn(1 – x)O (c)  (energy above the top of valence band), 0 is the permittivi-ty of free space, e is the electron charge, є is the dielectric constant and RDA is the donor-acceptor pair separation. The photoluminescence spectra of the three sets of sam-ples are shown in Fig. 3a, b and c. Considering the spectral information of all the sam-ples, strong peaks ranging from 370 nm to 391 nm were observed. A typical ZnO UV-exitonic emission band around 380 nm is observed, which is the characteristics of band edge emission. On being exposed to 280 nm radia-tion the prepared samples emits visible blue line. This visible emission is also evident from the photolumines-cence graph as shown in Fig. 3.   V. BANDYOPADHYAY, K. BHUSHAN, S. MUKHERJEE J. NANO- ELECTRON. PHYS. 5, 02030 (2013)   02030-4 Table 3 – Emission Wavelength by PL Emission Spectra  Sample Name Type of Particle Peak at Wavelength (nm) Fe0.02Zn0.98O Coated 383 Uncoated 382 Fe0.05Zn0.95O Coated 360 Uncoated 382 Ni0.02Zn0.98O Coated 370 Uncoated 381 Ni0.05Zn0.95O Coated 380 Uncoated 391 Mn0.02Zn0.98O Coated 385 Uncoated 382 Mn0.05Zn0.95O Coated 378 Uncoated 372  3.4 Magnetization Measurements  The magnetization responses of all the uncoated sam-ples were studied in a SQUID (Quantum Design). The M-H responses of the samples are shown in Fig. 4a, b and c. The sample doped with Mn shows the highest magnetic response whereas for Fe and Ni the response is extremely weak. The coercivity obtained for the samples and varies from 114 Oe to 189 Oe which is definitely more than other reports [15]. The ferromag-netic nature cannot be a consequence of metal-metal interaction because the medium in which the samples have been prepared do not have any reducing proper-ties. The ferromagnetic behaviour observed in the samples is probably due to competition between the double-exchange interaction and the antiferromagnetic       (a)       (b)    (c)  Fig. 4 – M-H curve at room temperature of Fe doped ZnO nanostructures (a), Ni doped ZnO nanostructures (b), Mn doped ZnO nanostructures  EVIDENCE OF ITINERANT FERROMAGNETISM IN… J. NANO- ELECTRON. PHYS. 5, 02030 (2013)   02030-5 superexchange interaction in the material. The low mag-netization and coercivity values measured for our samples are standard properties of nanocrystalline dilute magnetic semiconductors. Radovanovic [16] suggested the for-mation of dense aggregates of Ni-doped ZnO nanocrystals as responsible for observed ferromagnetism. Fig. 5 shows the ZFC and FC curves for the 5 % Fe doped ZnO nanocrystals. The observed monotonic fall suggests a thermodynamically equilibrium state reminis-cent of Curie’s law. A small hump at about 60 K may be attributed to presence of ferromagnetic re-entrant behav-iour.    Fig. 5 – Zero field cooled (ZFC) and field cooled (FC) magneti-zation as a function of temperature for 5 % Fe doped ZnO nanostructures 4. CONCLUSION  The present work was focused on synthesis of transi-tion metal doped ZnO nano crystals in methanol solution at room temperature and their structural, optical and magnetic characterization. Mn, Fe and Ni doped ZnO, doped in composition x  0.02 and 0.05 where synthe-sized by co-precipitation low entropy method. The crystal structure, magnetic properties and optical properties have been investigated by X-ray diffraction (XRD), SQUID, UV-Visible and PL spectroscopy respectively. The X-ray diffraction showed that the prepared sam-ples are single phase with the ZnO like wurtzite struc-ture. No secondary phase was found in XRD spectrum. The blue shift in the band gap of transition metal ion doped ZnO was observed in PL emission spectra. A band gap between 3.27 eV to 3.67 eV was calculated for differ-ent composition and different transition metal doping by UV Visible spectroscopy. The enhancement of the bang gap energy was attributed to the incorporation of dopant ion into the ZnO host structure. The magnetic responses the room temperature fer-romagnetic properties in 2 % Fe doped, 5 % Ni doped and 2 % Mn doped ZnO. 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Evidence of Itinerant Ferromagnetism in Transition Metal Doped ZnO Nanostructures

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