Shidaling Matteppanavar

Size Control and Magnetic Property Trends in Cobalt Ferrite Nanoparticles Synthesized Using an Aqueous Chemical Route

Cobalt ferrite (CoFe2O4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore, post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe2O4 nanoparticles with coercive magnetic flux density (Hc) in the range 5.5-31.9 kA/m and Ms in the range 47.9-84.9 A·m2Kg-1. At a grain size of ~ 54±2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in Hc. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe2O4 synthesis. The magnetic trends reported will aid in the optimization of functional CoFe2O4 nanoparticles.

Low temperature magnetic studies on PbFe0.5Nb0.5O3 multiferroic

PbFe0.5Nb0.5O3 (PFN), a well-known A(B′1/2B″1/2)O3 type multiferroic, was successfully synthesized in single phase by a single step solid state reaction method. The single phase PFN was characterized through XRD, microstructure through SEM, and magnetic studies were carried out through a temperature dependent vibrating sample magnetometer (VSM) and neutron diffraction (ND) measurements. PFN exhibits a cusp at around 150 K in the temperature dependent magnetic susceptibility corresponding to the Neel temperature (TN1) and another peak around 10 K (TN2) corresponding to spin-glass like transition. In the temperature dependent ND studies, a magnetic Bragg peak appears at Q=1.35 A−1 (where Q=4πsinθ/λ, is called the scattering vector) below TN (150 K) implying antiferromagnetic (AFM) ordering in the system. On the basis of Rietveld analysis of the ND data at T=2 K, the magnetic structure of PFN could be explained by a G-type antiferromagnetic structure.

Neutron diffraction studies on chemical and magnetic structure of multiferroic PbFe0.67W0.33O3

We report on the single phase synthesis and room temp. structural characterization of PbFe0.67W0.33O3 (PFW) multiferroic. The PFW was synthesized by low temp. sintering, Columbite method. Anal. of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed anal. of room temp. neutron diffraction (ND) reveals cubic phase at room temp., space group Pm-​3m. The ND pattern clearly reveals magnetic Bragg peak at 2θ = 18.51° (Q = 1.36A-​1)​. The refinement of magnetic structure reveals G-​type antiferromagnetic structure in PFW at room temp. The dielec. const. and loss tangent decreases with increasing frequency. The room temp. P-​E measurements shows a nonlinear slim hysteresis, typical nature of relaxor multiferroics, with satn. and remnant polarizations of Ps = 1.50 μC​/cm2 and Pr = 0.40 μC​/cm2, resp. (c) 2014 American Institute of Physics.We report on the single phase synthesis and room temperature structural characterization of PbFe0.67W0.33O3 (PFW) multiferroic. The PFW was synthesized by low temperature sintering, Columbite method. Analysis of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed analysis of room temperature neutron diffraction (ND) reveals cubic phase at room temperature, space group Pm-3m. The ND pattern clearly reveals magnetic Bragg peak at 2theeta = 18.51 (Q = 1.36{\AA}-1). The refinement of magnetic structure reveals G-type antiferromagnetic structure in PFW at room temperature. The dielectric constant and loss tangent decreases with increasing frequency. The room temperature P-E measurements shows a non-linear slim hysteresis, typical nature of relaxor multiferroics, with saturation and remnant polarizations of Ps = 1.50 microC/cm2 and Pr = 0.40 microC/cm2, respectively.We report on the single phase synthesis and room temperature structural characterization of PbFe{sub 0.67}W{sub 0.33}O{sub 3} (PFW) multiferroic. The PFW was synthesized by low temperature sintering, Columbite method. Analysis of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed analysis of room temperature neutron diffraction (ND) reveals cubic phase at room temperature, space group Pm-3m. The ND pattern clearly reveals magnetic Bragg peak at 2θ = 18.51° (Q = 1.36A{sup −1}). The refinement of magnetic structure reveals G-type antiferromagnetic structure in PFW at room temperature. The dielectric constant and loss tangent decreases with increasing frequency. The room temperature P-E measurements shows a non-linear slim hysteresis, typical nature of relaxor multiferroics, with saturation and remnant polarizations of P{sub s} = 1.50 μC/cm{sup 2} and P{sub r} = 0.40 μC/cm{sup 2}, respectively.

Effect of Sintering Temperature and Duration on the Formation of Single-Phase Pb0.9Bi0.1Fe0.55Nb0.45O3 Solid Solution

ABSTRACT Effect of sintering temperature and duration on single phase formation and structural properties of Pb0.9Bi0.1Fe0.55Nb0.45O3 (PBFNO) solid solution was investigated. The single step solid state reaction method was adopted to achieve the pure perovskite phase. Calcination was carried out at 700oC for 2 h and sintering at different temperatures as 800o, 850o, 900o, 950o, 1000o and 1050oC for 1 h and also at 800oC for 1-5 h to achieve the single phase in PBFNO solid solution. From the X-ray diffraction studies, it was found that sintering at 800oC for 3 h was optimum for achieving single phase and all the other conditions showed an impurity phase. Rietveld refinement was carried out on single phase PBFNO solid solution by using FullProf Suite, which confirmed the monoclinic structure with Cm space group and the obtained refinement parameters were Rp=15.7; Rw p=20.7, Rexp=16.72, χ2(Chi2)=1.54. The lattice parameters were: a=5.666(3) Å, b=5.667(4) Å, c=4.017(2) Å and α=γ=90o, β=89.943(4)o. Scanning electron micrograph showed an average grain size of ∼2 μm with uniform morphology. All the results clearly revealed the significance of low temperature and short duration sintering to control the single phase in PBFNO solid solution. GRAPHICAL ABSTRACT

Electric field-induced tuning of magnetism in PbFe0.5Nb0.5O3 at room temperature

We study the influence of electrical poling, carried out at room temperature, on the structure and magnetism of Pb(Fe0.5Nb0.5)O3 by analyzing the differences observed in structural and magnetic properties before and after the electrical poling. The changes observed in magnetization of Pb(Fe0.5Nb0.5)O3 before and after electrical poling exhibit considerably strong converse magnetoelectric effect at room temperature. In addition, the strengthening of Fe/Nb-O bond due to electrical poling is discussed on the basis of Raman spectral studies and analysis of neutron diffraction patterns. The potential tunability of magnetization with electrical poling can be an ideal tool for realization of application potential of this multiferroic material.

Neutron diffraction, Mössbauer and ferroelectric studies on magnetoelectric Pb0.9Bi0.1Fe0.55Nb0.45O3

Pb 0.9Bi0.1Fe0.55 Nb 0.45O3 (PBFNO) multiferroic materialwas synthesized through single step solid state reaction method with low sintering (800 °C for 3 hour) temperature. Single phase was confirmed through the X-Ray Diffraction (XRD), Neutron diffraction (ND) and Scanning Electron Microscopy (SEM) measurements. Rietveld refinement was performed on room temperature (RT) XRD and ND data by considering monoclinic structure with Cm space group. The obtained cell parameters from the refinement of ND data are a = 5.666(3) A, b = 5.667(4) A, c = 4.017(2) A and β = 89.943(4)° and are in good agreement with the XRD refinement data. The RT Mossbauer spectroscopy was used to investigate the magnetic ordering of PBFNO and it shows the paramagnetic behavior with the presence of Fe3+ states. RT ferroelectric (P-E) loops confirmed the existence of ferroelectric ordering in the PBFNO. The RT ferroelectric and antiferromagnetic properties are the evidence of magnetoelectric coupling.

Neutron diffraction, Mössbauer and electron paramagnetic resonance studies of Pb0.8Bi0.2Fe0.6Nb0.4O3 multiferroic

The Pb0.8Bi0.2Fe0.6Nb0.4O3 (PFN-BFO) multiferroic solid solution was synthesized by single step solid state reaction method with low calcination (700 °C/2h) and sintering (800 °C/3h) temperatures. Single phase formation was confirmed through X Ray Diffraction (XRD) and Neutron Diffraction (ND) at room temperature (RT). The structural analysis was carried out by Rietveld refinement through the Fullprof program. Refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.6449(8) A, b = 5.6536(5) A, c = 4.0017(6) A and β = 89.930(4)°. ND data at RT exhibits G-type antiferromagnetic structure. The Mossbauer and Electron Paramagnetic Resonance (EPR) spectroscopy studies were carried out at RT. The isomer shift and the quadrupole splitting of the Mossbauer spectra confirm the Fe in +3 states. An EPR spectrum shows a single broad slight asymmetric line, is an evidence of Fe in +3 states. ND, Mossbauer and EPR studies are the clear evid...

Breaking of ferrimagnetic ordering in Sc3+ doped Mn-Zn ferrites due to high energy Gamma irradiation

For the first time, we report the effect of high energy gamma irradiation induced structural and magnetic properties of nanocrystalline Mn0.5Zn0.5ScyFe2-yO4 (y = 0.01, 0.03 and 0.05) samples synthesized by solution combustion method using a mixture of fuels. All samples were exposed to a dose of 25 kGy gamma radiations originating from a 60Co source. The as prepared samples and the samples after gamma irradiation were characterized by X-ray diffraction, Fourier transform Infrared spectroscopy and vibrating sample magnetometry at RT. The XRD results reveal that all the pristine samples have shown single phase cubic structure before and after gamma irradiation. The lattice parameter increases on increasing Sc3+ content after gamma irradiation. FTIR reveals that, after gamma irradiation the absorption peaks are shifted to higher frequency. In M-H loops, we observe decrease in saturation magnetization, remnant and coercivity of the samples due to breaking of ferrimagnetic ordering, when a high energy gamma ra...

Structural, Magnetic and Dielectric Studies of Pb0.9Bi0.1Fe0.55Nb0.45O3 Multiferroic Solid solution

Single phase Pb0.9Bi0.1Fe0.55Nb0.45O3 (PFN-BFO) multiferroic solid solution was synthesized through single step solid state reaction method using low temperature annealing technique. The crystal structure, microstructure, magnetic and dielectric properties of PFN-BFO solid solution were investigated at room temperature (RT). Sintered samples were then subjected to XRD analysis and it revealed the formation of single phase without any impurities. The structural analysis was carried out by Rietveld Refinement technique through the Full Prof suite. The RT Rietveld refined XRD pattern confirms the monoclinic structure with Cm space group and obtained cell parameters are a = 5.666(3)A, b = 5.667(4)A, c = 4.017(2)A and p = 89.943(4)°. The surface morphology of the sample was studied by Scanning electron microscope (SEM) and average grain size was estimated to be ~5μm. M-H curve shows the weak ferromagnetic kind of behaviour with antiferromagnetic ordering. Room temperature dielectric constant, loss tangent and impedance spectroscopic data were measured at different frequencies (100Hz - 5MHz). The impedance spectroscopy reveals the contribution from the grains towards the electrical parameters.

Low temperature dielectric and impedance studies on magnetoelectric Pb(Fe0.5Nb0.5)O3 ceramic

The structural, microstructural, low temperature dielectric and impedance properties of Pb(Fe0.5Nb0.5)O3 (PFN) ceramic prepared by single step solid-state reaction method have been investigated. Processing parameters such as calcination, sintering temperature and sintering durations were optimized to get better dielectric properties. It was found that the above ceramics sintered at 1050 °C for 4 hr exhibited single phase, maximum density and uniform microstructure. X-ray diffraction (XRD) and neutron diffraction (ND) reveals that the system exhibit single phase without any kind of secondary phases at room temperature (RT) with monoclinic crystal structure (Cm). Surface morphology of the compounds was studied by Scanning electron microscope (SEM). Impedance spectroscopy is used to study the electrical behaviour of PFN in the frequency range from 100Hz to 1MHz and in the temperature range from 120 to 293 K. The frequency-dependent electrical data are analyzed by impedance formalisms. The complex impedance s...