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Anionic polymerization in Co and Fe doped ZnO: Nanorods, magnetism and photoactivity
Jasneet Kaur,R.K. Kotnala,Vinay Gupta,Kuldeep Chand Verma 한국물리학회 2014 Current Applied Physics Vol.14 No.5
The growth mechanism of Zn1xCoxO (ZC) and Zn1xFexO (ZF) nanorods, and resulting magnetic and optical properties have been studied. The ZC and ZF nanorods were prepared by solegel synthesis route. X-ray diffraction results in polycrystalline phase with wurtzite structure of ZC and ZF nanorods. The transmission electron microscopy images show the formation of nanorods. The growth mechanism of nanorods is explained on the basis of agglomeration of Zn2þ with OH ions which is react with poly vinyl alcohol involve anionic polymerization of oriented growth. Magnetic measurement of ZC and ZF nanorods exhibit superferromagnetic behavior and the large value of saturation magnetization observed at room temperature. The magnetization below room temperature measurement confirms the origin of observed magnetism. Raman and photoluminescence spectra show good photoactivity. The observed Raman active modes show wurtzite structure belongs to C6v symmetry group. Photoluminescence measurements of ZC and ZF nanorods exhibit ultraviolet peaks at 413.90 nm (w3 eV) due to free exciton emission and at 546.31 nm (w2.27 eV) due to transition from deep donor states which arises from oxygen vacancy.
Kuldeep Chand Verma,R.K. Kotnala 한국물리학회 2016 Current Applied Physics Vol.16 No.2
We have reported the long-range ferromagnetic interactions in La and Gd doped Zn0.95Co0.05O (ZCO5) [Zn0.92Co0.05La0.03O (ZCLO53) and Zn0.92Co0.05Gd0.03O (ZCGO53)] nanostructures due to defects that formed by lattice deformation and vacancies. These nanostructures were prepared by solegel method. Xray diffraction shows hexagonal Wurtzite ZnO and the lattice parameters are highly influenced by doping. TEM analysis depicted nano-aggregation type product. FTIR spectra have shown organic contribution and metal-oxygen vibrational band in the samples. The Wurtzite structure with La and Gd doping in ZCO5 is also confirmed by Raman modes with introducing lattice defects, vacancies and interstitials formation. Both the band gap energy and defects related vacancies performed PL emission. The long-range ferromagnetic order occurs due to strong antiferromagnetic interactions that performed by La and Gd doping in ZCO5. It results into antiferromagnetic 3d, 4fe3d, 4fe5de4f transitions. The zero-field and field cooling at H ¼ 500 Oe in the temperature region, T ¼ 300e5 K is used to evaluate the blocking temperature of phase transition. Here, the medium for long-range ferromagnetic interactions is defect carriers. The bound magnetic polaron model has been described the resulting magnetic behavior. The chemical valance states of La3þ and Gd3þ induce superexchange magnetic interaction due to F-center mechanism.
White Light Emitting Magnetic ZnO:Sm Nanoparticles Prepared by Inclusive Co-Precipitation Synthesis
Santa Chawla,Monica Saroha,R.K. Kotnala 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.1
Inclusion of rare earth Samarium as dopant in nanoparticles of ZnO has been achieved by co-precipitation in highly alkaline medium near room temperature. Substitutional doping of Sm in Zn position in the ZnO lattice could be inferred through change in lattice parameters in response to Sm doping concentration. Dopant Sm enhances broad visible emission of ZnO thus making it a bright white light emitter under UV (300 - 380 nm) excitation. Observation of room temperature intrinsic ferromagnetism with optimal Sm doping in ZnO:Sm suggests unpaired spin in Sm3+ at zinc substitutional sites could create spin ordering and long range ferromagnetic coupling. Such white light emitting magnetic nanoparticles of ZnO:Sm can have immense potential as LED phosphor and spin LED semiconductor.
Red Upconversion Luminescence and Paramagnetism in Er/Yb Doped SnO2
Shweta Sharma,Jyoti Shah,R.K. Kotnala,Santa Chawla 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.5
Red upconversion luminescence has been introduced in functional semiconductor SnO2 by doping rare earth ions Er3+ and Yb3+ and using 980 nm diode laser as pump source. High temperature solid state reaction leads to incorporation of trivalent lanthanide ions in SnO2. For high concentrations of lanthanide doping,partial reduction of Sn4+ to Sn2+ occurs for charge compensation making the material system SnO2-SnO alloy. Upconverting SnO2 exhibits paramagnetic characteristics with magnetization increasing with introduction of trivalent rare earth ions Er3+/Yb3+.
Study of structural, electrical and magnetic properties of Cr doped Ni–Mg ferrite nanoparticle
Hashim, M.,Meena, S. S.,Kotnala, R. K.,Shirsath, S. E.,Roy, A. S.,Parveen, A.,Bhatt, P.,Kumar, S.,Jotania, R. B.,Kumar, R. Elsevier Science B.V., Amsterdam. 2014 Journal of Alloys and Compounds Vol.602 No.-
Electrical and magnetic properties of rare earth substituted strontium hexaferrites
Anterpreet Singh,S. Bindra Narang,Kulwant Singh Thind,O.P. Pandey,R.K. Kotnala 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.2
Samples of strontium ferrite (Sr-M) with different molar substitution concentrations of lanthanum, neodymium and samarium ions were prepared by a standard ceramic processing technique. AC conductivity, dielectric constant and dielectric loss tangent measurements were carried out in the frequency range of 20 Hz to 1MHz. The experimental results indicate that AC electrical conductivity increases with increasing frequency. The increase in AC conductivity with frequency can be explained on the basis of Koops model, whereas the dielectric constant and dielectric loss tangent variations have been explained with a Maxwell-Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The effects of rare earth substitution on the magnetic properties such as the saturation magnetization moment (Ms), coercive field (Hc), remenance (Mr),and Curie temperature Tc (K) have been investigated. It is found that the values of the magnetization moment (Ms), and remenance (Mr) decrease with increasing rare earth ions substitution for all the series. The reason for the decrease may be both the magnetic dilution and spin canting, which promote reduction of superexchange interactions. The enhancement of Hc values may be due to higher magnetocrystalline anisotropy, where Fe2+ ion anisotropy on the 2a site could be dominant in all hexaferrites series.