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Lakshmi C.S.,Regency Institute of Technology | Sridhar C.S.L.N.,Vignana Bharathi Institute of Technology | Govindraj G.,Pondicherry University | Bangarraju S.,Andhra University | Potukuchi D.M.,Jawaharlal Nehru Technological University Kakinada
Journal of Materials Science | Year: 2016

Structural, morphological, magnetic, and dielectric investigations are carried out in Nb-doped (viz., for x equal to 0.0–0.4 by wt%) nanocrystalline Ni–Zn ferrites synthesized by hydrothermal method. XRD, IR studies infer the growth of nano structures and Fe2O3 phase. Nb ions segregate at grain boundaries. Crystallite size (D) varies from 62 to 18 nm with x. FTIR absorption exhibits split at higher x. Saturation magnetization witnesses an overall decrease with x. Trends of Ms(x) are explained by nature of dopant, preferential replacement, surface canting (Y–K angles) and lattice contraction. Variations of coercive field (Hc) and D infer single-domain to multi-domain morphological transformation. Occurrence of superparamagnetism (SPM) is predicted for zeroed values of Hcand for a critical concentration xcrit equal to 0.321. Enhanced Nb5+–Fe2+ binding with dopant (x up to 0.2) results for decrease in dielectric constant (Formula presented.), loss factor tanδ and increase in resistivity ρ. Lowered ac conductivity is attributed to blockade of path by Nb5+ ions in the vicinity of B-sites. Relatively higher ρ (~108 Ω cm) and lower loss (tanδ ~10−2–10−3) evinced for 10 kHz. Enhanced core loss is realized with x manifested as lowered Hc and tanδ to usher their utility in high-frequency applications. © 2016 Springer Science+Business Media New York Source

Sridhar C.S.L.N.,Vignana Bharathi Institute of Technology | Lakshmi C.S.,Regency Institute of Technology | Govindraj G.,Pondicherry University | Bangarraju S.,Andhra University | And 2 more authors.
Journal of Physics and Chemistry of Solids | Year: 2016

Nano-phased doped Mn-Zn ferrites, viz., Mn0.5-x/2Zn0.5-x/2SbXFe2O4 for x=0 to 0.3 (in steps of 0.05) prepared by hydrothermal method are characterized by X-ray diffraction, Infrared and scanning electron microscopy. XRD and SEM infer the growth of nano-crystalline cubic and hematite (α-Fe2O3) phase structures. IR reveals the ferrite phase abundance and metal ion replacement with dopant. Decreasing trend of lattice constant with dopant reflects the preferential replacement of Fe3+ions by Sb5+ion. Doping is found to cause for the decrease (i.e., 46-14 nm) of grain size. An overall trend of decreasing saturation magnetization is observed with doping. Low magnetization is attributed to the diamagnetic nature of dopant, abundance of hematite (α-Fe2O3) phase, non-stoichiometry and low temperature (800 °C) sintering conditions. Increasing Yafet-Kittel angle reflects surface spin canting to pronounce lower Ms. Lower coercivity is observed for x≤0.1, while a large Hc results for higher concentrations. High ac resistivity (~106 ohm-cm) and low dielectric loss factor (tan δ~10-2-10-3) are witnessed. Resistivity is explained on the base of a transformation in the Metal Cation-to-Oxide anion bond configuration and blockade of conductivity path. Retarded hopping (between adjacent B-sites) of carriers across the grain boundaries is addressed. Relatively higher resistivity and low dielectric loss in Sbdoped Mn-Zn ferrite systems pronounce their utility in high frequency applications. © 2016 Elsevier Ltd. Source

Lakshmi C.S.,Regency Institute of Technology | Sridhar C.S.L.N.,Vignana Bharathi Institute of Technology | Govindraj G.,Pondicherry University | Bangarraju S.,Andhra University | Potukuchi D.M.,Jawaharlal Nehru Technological University Kakinada
Physica B: Condensed Matter | Year: 2015

Nanocrystalline Ni-Zn-Sb ferrites synthesized by hydrothermal method are reported. Influence of Sb5+ ions on structural, magnetic and dielectric properties of ferrites is studied. Phase identification, lattice parameter and crystallite size studies are carried out using by X-ray diffraction (XRD). Addition of dopant resulted for decrease in lattice parameter. Crystallite size gets reduced from 62 nm to 38 nm with doping of Antimony. Crystallite size and porosity exhibit similar trends with doping. Morphological study is carried out by Field Emission Scanning Electron Microscopy (FESEM). Strong FTIR absorption bands at 400-600 cm-1 confirm the formation of ferrite structure. Increase of porosity is attributed to the grain size. Doping with Antimony results for decrease in saturation magnetization and increase in coercivity. An initial increase of saturation magnetization for x=0.1 is attributed to the unusually high density. Reversed trend of coercivity with crystallite size are observed. Higher value of dielectric constant ε′(ω) is attributed to the formation of excess of Fe2+ ions caused by aliovalent doping of Sb5+ ions. Variation of dielectric constant infers hopping type of conductivity mechanism. The dielectric loss factor tanδ attains lower values of ~10-2. High ac resistivity ρ(ω) of 108 ω cm is witnessed for antimony doped ferrites. Higher saturation magnetization and enhanced dielectric response directs for a possible utility as microwave oscillators and switches. © 2014 Elsevier B.V. All rights reserved. Source

Prasad M.N.M.,Andhra University | Hussain M.A.,Andhra University | Sastry C.V.,Regency Institute of Technology
Journal of Theoretical and Applied Information Technology | Year: 2014

NTRU Labs have proposed a scheme for secure transmission using ring of truncated polynomials in Zq(x) / (xn -1). We have proved in this paper that a pre-processing the data to be transmitted greatly decreases the time of transmission. We have used a matrix version of NTRU Cryptosystems. © 2005 - 2014 JATIT & LLS. All rights reserved. Source

Uma Maheswara Rao C.,Andhra University | Bala Murali Krishna V.,Regency Institute of Technology | Laxmi Soundarya A.,JNTUH College of Engineering | Krishna Kumari N.,JNTUH College of Engineering
International Journal of Control Theory and Applications | Year: 2015

This paper proposes to describe Field oriented control (FOC) of Permanent Magnet Synchronous motor (PMSM) using Model Reference Adaptive control System (MRAS) speed observer for sensorless control of drive. The objective of the proposed sensorless control is to improve the speed control performance and robustness of PMSM drive under load variations. In this work, the conventionally used PI controller in adaption mechanism of the MRAS observer is replaced by a FLC. The improvement in speed response during load variations is shown by comparative study between conventional PI and fuzzy PI. The effectiveness and validity of the proposed control approach is verified by simulation results. © International Sciences Press, India. Source

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