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Srinivas A.,Advanced Magnetics Group | Krishnaiah R.V.,Advanced Magnetics Group | Karthik T.,Advanced Functional Materials Laboratory | Suresh P.,University of Hyderabad | And 2 more authors.
Applied Physics Letters | Year: 2012

A particulate composite consisting of 65 mol. % Na 0.5Bi 0.5TiO 3 and 35 mol. % CoFe 2O 4 was synthesized, and it's structure, microstructure, ferroelectric, magnetostrictive, magnetic, and direct/indirect magnetoelectric properties were studied. The composite showed different magnetization behaviour under electrically poled and un-poled conditions. The percentage change in magnetization as a result of poling is approximately -15% at 500 Oe magnetic field. Magnetostriction measurements displayed a value of λ 11 = -57 × 10 -6 and piezomagnetic coefficient δλ 11/δH = 0.022 × 10 -6 kOe -1 at 2.2 kOe for the composite. The maximum magnetoelectric output varied from 1350 mV/cm to 2000 mV/cm with change in the electrical poling conditions. © 2012 American Institute of Physics.

Sakar M.,University of Madras | Balakumar S.,University of Madras | Saravanan P.,Advanced Magnetics Group | Jaisankar S.N.,CSIR - Central Leather Research Institute
AIP Conference Proceedings | Year: 2013

Bismuth ferrite (BFO) nanoparticles were synthesized by auto-ignition technique with and without adding ignition fuel such as citric acid. The presence of citric acid in the reaction mixture yielded highly-magnetic BFO/γ-Fe2O3 nanocomposite. When this composite was annealed to 650°C, a single phase BFO was formed with average crystallite size of 50 nm and showed weak ferromagnetic behavior. Conversely, the phase pure BFO prepared without adding citric acid exhibited antiferromagnetism because of its larger crystallite size of around 70 nm. The visible-light driven photocatalytic activity of both the pure BFO and BFO/γ-Fe 2O3 nanocomposite were examined by degrading methyl orange dye. The pure BFO showed a moderate photocatalytic activity; while BFO/γ-Fe2O3 nanocomposite showed enhanced activity. This could be probably due to the optimal band gap ratio between BFO and γ-Fe2O3 phases reduced the recombination of electron-hole pairs which aided in the enhancement of photocatalytic activity. © 2013 American Institute of Physics.

Rajasekhar M.,Indian Institute of Technology Kharagpur | Rajasekhar M.,Advanced Magnetics Group | Rajasekhar M.,French National Center for Scientific Research | Ram S.,Indian Institute of Technology Kharagpur | Akhtar D.,Advanced Magnetics Group
Journal of Magnetism and Magnetic Materials | Year: 2013

Effects of partial substitution of nonmagnetic Sn for Fe on elevated temperature magnetic properties in exchange-coupled Nd2Fe 14B/(Fe3B, z-Fe) nanocomposites have been investigated. Thermal stability of remanent magnetization (Jr) and coercivity (Ic) is found to increase on Sn substitution. The absolute values of the temperature coefficients dJj and β(Hc) decrease from 0098 and 0323 to 0061 and 0288, respectively with increase in Sn content from 0 to 1.5 at%. Influence of non-ideal microstructure and exchange coupling on the coercivity has been studied by analyzing the microstructural parameters αK αex and Neff determined from the temperature dependence of the coercivity. Substitution of Sn significantly decreases the value of N eff from 0042 to 0005 indicating a decrease in the local stray fields at the grain boundary. © 2013 Elsevier BY. All rights reserved.

Karthik T.,Anna University | Karthik T.,Indian Institute of Technology Hyderabad | Srinivas A.,Advanced Magnetics Group | Kamaraj V.,Anna University | Chandrasekeran V.,Advanced Magnetics Group
Ceramics International | Year: 2012

Polycrystalline single phase BiFeO 3 (BFO) ceramic samples have been prepared by conventional solid state sintering and also by in-situ magnetic field pressing followed by solid state sintering. The influence of in-situ magnetic field pressing on the structural, magnetic, ferroelectric and thermal properties has been investigated in this work. X-ray diffraction analysis and Reitveld refinement shows the single phase characteristics of BFO samples. Further texture formation and the development of compressive lattice strain have been observed in the magnetic field pressed samples. A change in Fe-O-Fe bond angle and suppression of spiral spin structure results in the enhanced magnetization value M s = 136 memu/g at 2 T. Similarly spontaneous polarization has also improved with a P max value of 1.3 μC/cm 2. DSC plot shows a significant variation in heat flow and enthalpy at the Neel transition (T N = 372 °C) and ferro to paraelectric transition (T C = 820 °C) for the magnetic field pressed BFO samples. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Ramesh Kumar K.,Indian Institute of Technology Madras | Arout Chelvane J.,Advanced Magnetics Group | Markandeyulu G.,Indian Institute of Technology Madras | Malik S.K.,University of Brasilia | Harish Kumar N.,Indian Institute of Technology Madras
Solid State Communications | Year: 2010

Mn2 - x Cox V Ga (x = 0.5, 0.75 and 1) compounds were synthesized by arc melting to investigate the effect of cobalt substitution on the magnetic and transport properties of the half-metallic ferrimagnetic compound Mn2VGa. The lattice parameter value decreases with the substitution of Co. The compounds Mn1.25Co0.75VGa and MnCoVGa showed a substantial reduction in magnetic moment due to anti-parallel alignment of the Mn moment with Co and V moments and the Mz value for these compounds observed to be 0.35 μB and 0.37 μB respectively. The magnetic moment per formula unit at 5 K, estimated from magnetization data, indicates a slight deviation from the Slater-Pauling relation. The Curie temperature was found to decrease with the Co substitution. Low temperature resistivity data in the temperature range of 18-100 K was observed to follow the relation ρ = ρ0 + A T2 + B T4.5. © 2009 Elsevier Ltd. All rights reserved.

Datt G.,Indian Defence Institute of Advanced Technology | Sen Bishwas M.,CSIR - National Chemical Laboratory | Manivel Raja M.,Advanced Magnetics Group | Abhyankar A.C.,Indian Defence Institute of Advanced Technology
Nanoscale | Year: 2016

Magnetic anomalies corresponding to the Verwey transition and reorientation of anisotropic vacancies are observed at 151 K and 306 K, respectively, in NiCoFe2O4 nanoparticles (NPs) synthesized by a modified-solvothermal method followed by annealing. Cationic disorder and spherical shape induced non-stoichiometry suppress the Verwey transition in the as-synthesized NPs. On the other hand, reorientation of anisotropic vacancies is quite robust. XRD and electron microscopy investigations confirm a single phase spinel structure and the surface morphology of the as-synthesized NPs changes from spherical to octahedral upon annealing. Rietveld analysis reveals that the Ni2+ ions migrate from tetrahedral (A) to octahedral (B) sites upon annealing. The Mössbauer results show canted spins in both the NPs and the strength of superexchange is stronger in Co-O-Fe than Ni-O-Fe. Magnetic force images show that the as-synthesised NPs are single-domain whereas the annealed NPs are multi-domain octahedral particles. The FMR study reveals that both the NPs have a broad FMR line-width; and resonance properties are consistent with the random anisotropy model. The broad inhomogeneous FMR line-width, observation of the Verwey transition, tuning of the magnetic domain structure as well as the magnetic properties suggest that the NiCoFe2O4 ferrite NPs may be promising for future generation spintronics, magneto-electronics, and ultra-high-density recording media as well as for radar absorbing applications. © The Royal Society of Chemistry 2016.

Raja M.M.,Advanced Magnetics Group | Kamat S.V.,Advanced Magnetics Group
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2015

The effect of substitution of Co for Fe on structure, magnetic, and electrical resistivity of Heusler-type Fe3−xCoxSi (0 ≤ x ≤ 1) alloys was investigated using X-ray powder diffraction, 57Fe Mössbauer spectroscopy, magnetic, and electrical transport measurements. The results revealed that these alloys consist of ordered DO3 phase and some L21 phase up to x ≤ 0.5. However, for x > 0.5, the alloys consisted of L21 ordered phase and B2 disordered phase. The magnetization value was close to that predicted from Slater-Pauling rule for x ≥ 0.5 alloys. The Curie temperature increased from 832 K (559 °C) for x = 0 (Fe3Si) alloy to 1016 K (743 °C) for x = 1 (Fe2CoSi) alloy. Electrical transport studies revealed the presence of half-metallic behavior at low temperatures in x ≥ 0.5 alloys. No half-metallic behavior was observed for x = 0 and 0.25 alloys; however, a high resistivity with ferromagnetism was observed in these alloys, which is desirable for ferromagnetic metal/semiconductor spintronic devices. © 2015, The Minerals, Metals & Materials Society and ASM International.

Srinivas M.,Advanced Magnetics Group | Majumdar B.,Advanced Magnetics Group | Phanikumar G.,Indian Institute of Technology Madras | Akhtar D.,Advanced Magnetics Group
Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science | Year: 2011

The effect of planar flow melt spinning (PFMS) parameters on the continuity, surface quality, and structure of 10-mm-wide Fe 68.5Si18.5B9Nb3Cu1 ribbons has been investigated. The change in shape and stability of the melt puddle as a function of the processing parameter was studied using a high-speed imaging system and was correlated to ribbon formation. A window of process parameters for obtaining continuous ribbons with good surface quality has been evaluated. It has been observed that thinner ribbons are found to be more continuous because of higher ductility. The higher melt temperature leads to the formation of crystalline phase in as-spun ribbons, and this deteriorates the soft magnetic properties on annealing. The experimental results are corroborated with the numerical estimates, which suggest that the critical thickness for amorphous phase formation decreases with increasing initial melt temperature. © The Minerals, Metals & Materials Society and ASM International 2011.

Suresh G.,Vellore Institute of Technology | Saravanan P.,Advanced Magnetics Group | Rajan Babu D.,Vellore Institute of Technology
Journal of Physics: Conference Series | Year: 2011

Fe-Co nanoparticles stabilized by polyvinylpyrrolidone (PVP) have been prepared using modified polyol process. When 5 mmol of PVP was used, aggregated nanoparticles with irregular shapes were resulted; whereas on increasing the PVP concentration to 10 mmol, highly spherical nanoparticles were obtained. In the present work, the influence of non-ionic stabilizer viz. PVP on the synthesis of spherical nanoparticles and their structural, macromagnetic properties have been reported.

Durga Rao T.,Indian Institute of Technology Hyderabad | Karthik T.,Indian Institute of Technology Hyderabad | Srinivas A.,Advanced Magnetics Group | Asthana S.,Indian Institute of Technology Hyderabad
Solid State Communications | Year: 2012

The polycrystalline Bi 1-xHo xFeO 3 (x=0, 0.05, 0.1) compounds were synthesized by conventional solid-state route. Rietveld refinement revealed that all the compounds were stabilized in rhombohedral structure with R3c (IUCr No. 161) space group. Room temperature magnetic measurements revealed that Ho substitution induces ferromagnetism and improves the magnetic properties of BiFeO 3. A competing ferro and anti-ferro magnetic interaction was observed in these compounds. Temperature variation of complex impedance studies revealed that electrical properties are improved with the Ho substitution. The ac conductivity found to obey universal power law and showed the negative temperature coefficient of resistance character. Correlated barrier hopping model (CBH) was employed to explain the frequency and temperature dependence of ac conductivity and the mechanism of transport in the material BFO and Ho substituted BFO. Density of states near Fermi level was calculated by using the ac conductivity data. © 2012 Elsevier Ltd.

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