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    Electrical properties and hyperfine interactions of boron doped Fe3O4 nanoparticles
    (Academic Press, 2015) Amir, Md.; Ünal, Bayram; Geleri, M.; Güngüneş, Hakan; Shirsath, Sagar E.; Baykal, Abdulhadi
    The single spinel phase nano-structured particles of FeBxFe2-xO4 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) were synthesized by the glycothermal method and the effect of B3+ substitution on structural and dielectric properties of Fe3O4 were studied. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on B3+ substitution have been determined. The hyperfine field values at B- and A-sites gradually decrease with increasing B3+ ion concentration (x). The cation distributions obtained from Bertaut method are in line with Mössbauer results. Complex impedance analysis of boron-substituted spinel ferrites have been made extensively in order to investigate the significant changes in ac and dc conductivity as well as complex permittivity when the boron composition ratio varies from 0.1 to 0.5. It is found that both ac and dc conductivity are also dependent on the boron content in addition to both temperature and applied frequency. The dc conductivity tendency does not purely obey the Arrhenius plots. The dielectric constant and loss of complex permittivity, in general, show similar attitudes as seen in some nanocomposites containing spinel ferrites except for some fluctuations and shifts along the characteristics of the curves. Furthermore, their imaginary components of both permittivity and modulus are almost found to obey the power law with any exponent values varying between 0.5 and 2 in accordance with the level of boron concentrations. © 2015 Elsevier Ltd. All rights reserved.
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    Magnetic properties of FeMnyCoyFe2?2yO4@Oleylamine nanocomposite with cation distribution
    (Springer New York LLC, 2017) Amir, Md.; Demir Korkmaz, Ayşe; Baykal, Abdulhadi; Geleri, M.; Sözeri, Hüseyin; Güngüneş, Hakan; Sertkol, Murat; Shirsath, Sagar E.
    In this study, oleylamine (OAm) capped FeMnyCoyFe2?2yO4 (0.0???y???0.4) nanocomposites (NCs) were prepared via the polyol route and the impact of bimetallic Co3+ and Mn3+ ions on the structural and magnetic properties of Fe3O4 was investigated. The complete characterization of FeMnyCoyFe2?2yO4@OAm NCs were done by different techniques such as XRD, SEM, TGA, FT-IR, TEM, and VSM. XRD analyses proved the successful formation of mono-phase MnFe2O4 spinel cubic products free from any impurity. The average crystallite sizes were calculated in the range of 9.4–26.4 nm using Sherrer’s formula. Both SEM and TEM results confirmed that products are nanoparticles like structures having spherical morphology with small agglomeration. Ms continued to decrease up to Co3+ and Mn3+ content of y?=?0.4. Although Mössbauer analysis reveals that the nanocomposites consist three magnetic sextets and superparamagnetic particles are also formed for Fe3O4, Co0.2Mn0.2Fe2.6O4 and Co0.4Mn0.4Fe2.2O4. Cation distributions calculation was reported that Co3+ ions prefer to replace Fe2+ ions on tetrahedral side up to all the concentration while Mn3+ ions prefer to replace Fe3+ ions on the octahedral.
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    Synthesis and characterization of oleylamine capped MnxFe1-xFe2O4nanocomposite: Magneto-optical properties, cation distribution and hyperfine interactions
    (Elsevier Ltd, 2016) Güner, Sadık; Baykal, Abdulhadi; Amir, Md.; Güngüneş, Hakan; Geleri, M.; Sözeri, Hüseyin; Shirsath, Sagar E.; Sertkol, Murat
    Pure Fe3O4 NPs and Oleylamin (OAm) capped MnxFe1-xFe2O4 (MnxFe1-xFe2O4@OAm) (0.2 ? x ? 1.0) nanocomposites (NCs) were synthesized by the polyol route. Lattice parameter increases with increasing Mn2+ concentration, due to the respective larger ionic radius of Mn2+ ion compared with the Fe2+ ion. The VSM analyses revealed superparamagnetic characteristics of all samples. The extrapolated specific saturation magnetization (?s) values decreased from maximum 50.74 emu/g to minimum 15.34 emu/g by increasing Mn content. The particle size dependent Langevin function was applied to determine the magnetic particle dimensions (Dmag) between 9.10 nm and 21.50 nm. The observed magnetic moments of NPs and NCs are in range of (0.64–2.10) ?B and significantly less than 4 ?B of bulk Fe3O4. Magnetic anisotropy was determined as uniaxial and calculated effective anisotropy constants (Keff) are between 32.14 × 104 Erg/g and 8.71 × 104 Erg/g. The size dependent saturation magnetization suggests the existence of a magnetically dead layers around the magnetic cores for NCs between 0.72 nm and 1.29 nm. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Mn2+ substitution have been determined. Although, the Mössbauer spectra for the sample x = 0.2 is composed of ferromagnetic sextets, paramagnetic doublet is also formed for other samples. The percent diffuse reflectance spectroscopy (DR %) and Kubelka-Munk theory were used to specify the optical properties. The estimated optical band gap (Eg) values from Tauc plots are between 1.50 eV and 2.05 eV. Increasing Mn content in NCs increased the band gap at different magnitudes.