Neutron Diffraction Studies on Chemical and Magnetic Structure of Multiferroic PbFe0.67W0.33O3

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.Comment: 3 pages, 5 figures, conferenc

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 (H-c) in the range 5.5-31.9 kA/m and M-s in the range 47.9-84.9 A.m(2)Kg(-1). At a grain size of similar to 54 +/- 2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in H-c. 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 nanoparticle

Investigation on structural, Mossbauer and ferroelectric properties of (1-​x)​PbFe0.5Nb0.5O3-​(x)​BiFeO3 solid solution

(1-​X)​PbFe0.5Nb0.5O3(PFN)​-​(x)​BiFeO3(BFO) multiferroic solid solns. with x = 0.0, 0.1, 0.2, 0.3 and 0.4 were synthesized through single step solid state reaction method and characterized thoroughly through x-​ray Diffraction (XRD)​, SEM, Fourier Transform Infra-​Red (FTIR)​, Raman, Mossbauer spectroscopy and ferroelec. studies. The room temp. (RT) XRD studies confirmed the formation of single phase with negligible amt. of secondary phases (x = 0.2 and 0.4)​. The zoomed XRD patterns of (1-​x)​PFN-​(x)​BFO solid solns. showed the clear structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x = 0.4. The Raman spectra of the (1-​x)​PFN-​(x)​BFO solid solns. showed the compn. dependent phase transition from monoclinic (Cm) to rhombohedral (R3c)​. With increasing x in PFN, the modes related monoclinic symmetry changes to those of rhombohedral symmetry. The RT Mossbauer spectroscopy results evidenced the existence of compn. dependent phase transition from paramagnetic to weak antiferromagnetic ordering and weak antiferromagnetic to antiferromagnetic ordering. The Mossbauer spectroscopy showed paramagnetic behavior with a doublet for x = 0.0, 0.1 and 0.2 are shows the weak antiferromagnetic with paramagnetic ordering. For x = 0.3 and 0.4 shows the sextet pattern and it is a clear evidence of antiferromagnetism. The ferroelec. (P-​E) loops at RT indicate small polarization, as the x concn. increases in PFN, the remnant polarization and coercive field were decreased, which may due to the increase in the cond. and leaky behavior of the samples

Enhanced Humidity Sensing Response in Eu³⁺-Doped Iron-Rich CuFe₂O₄: A Detailed Study of Structural, Microstructural, Sensing, and Dielectric Properties

The CuFe(2−x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticles are synthesized by solution combustion method. The influence of Eu3+ on the structural, morphological, dielectrical, and humidity sensing study is recorded. The XRD pattern peaks of the as-prepared CuFe(2−x)EuxO4 (where x = 0.00, 0.01, 0.02, 0.03) nanoparticle confirm the polycrystalline spinel cubic structure with a small amount of CuO impurity phase at 38.87° and 48.96°. Surface morphology of the samples was studied by scanning electron microscope (SEM) images of the nanoparticles, and their respective average grain size was estimated using Image software. Chemical composition of all prepared samples was analyzed by EDS spectra. The dielectric parameters of AC conductivity, electric modulus, and impedance of the samples were measured over a range of frequencies from 0.1 KHz to 1 MHz at room temperature. Europium-doped copper ferrite samples showed good humidity sensing response, response and recover times, and stability over a %RH range of 11–91%. These types of samples are very useful for sensor application, battery applications, electronic applications, and automotive applications

Realization of Z2_2 Topological Metal in Single-Crystalline Nickel Deficient NiV2_2Se4_4

Temperature-dependent electronic and magnetic properties are reported for a Z2 topological metal single-crystalline nickel-deficient NiV$_2$Se$_4$. It is found to crystallize in the monoclinic Cr3S4 structure type with space group I2=m. From single-crystal x-ray diffraction, we find that there are vacancies on the Ni site, resulting in the composition Ni0:85V2Se4 in agreement with our electron-probe microanalysis. The electrical resistivity shows metallic behavior with a broad anomaly around 150{200 K that is also observed in the heat capacity data. This anomaly indicates a change of state of the material below 150 K. We believe that this anomaly could be due to spin fluctuations or charge-density-wave (CDW) fluctuations, where the lack of long-range order is caused by vacancies at the Ni site of Ni0:85V2Se4. Although we fail to observe any structural distortion in this crystal down to 1.5 K, its electronic and thermal properties are anomalous. The observation of non-linear temperature dependence of resistivity as well as an enhanced value of the Sommerfeld coefficient = 104.0(1) mJ/molK2 suggests strong electron-electron correlations in this material. The first-principles calculations performed for NiV$_2$Se$_4$, which are also applicable to Ni0:85V2Se4, classify this material as a topological metal with Z2 = (1; 110) and coexisting electron and hole pockets at the Fermi level. The phonon spectrum lacks any soft phonon mode, consistent with the absence of periodic lattice distortion in the present experiments.Comment: arXiv admin note: text overlap with arXiv:cond-mat/0610166 by other author

Composition dependent room temperature structure, electric and magnetic properties in magnetoelectric Pb(Fe 1/2 Nb 1/2 )O 3 Pb(Fe 2/3 W 1/3 )O 3 solid-solutions

We report on the studies of room temperature (RT) crystal structure, electric and magnetic properties of (1-x) Pb(Fe1/2Nb1/2)O-3 - x Pb(Fe2/3W1/3)O-3 (PFN1-x - PFWx) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions through the measurements of X-ray diffraction, FTIR, scanning electron microscopy (SEM), Neutron diffraction, Raman, Magnetic, Mossbauer and ferroelectric measurements. FTIR spectra showed two main perovskite related transmission bands. The SEM analysis shows an average grain size of 2 mm for all the solid solutions. Rietveld refinement was performed on RT X-ray diffraction (XRD) and neutron diffraction (ND), which reveals, the monoclinic phase for x = 0.0 with space group Cm and Cubic phase for x = 1.0 with space group Pm-3m. In other words, increasing x, the samples exhibit a gradual phase transition from monoclinic to cubic. In addition, the Raman spectroscopy corroborates the change in structural symmetry from monoclinic (Cm) to cubic (Pm-3m) on varying x. The coexistence of both monoclinic and cubic symmetries was observed between x = 0.2-0.8. Magnetic measurements shows that, the magnetic phase transition from paramagnetic to antiferromagnetic (AFM) was observed at or above RT for x = 0.6 and above. The magnetic structure was refined using the propagation vector k = (1/2, 1/2, 1/2) and structure was found to be G-type antiferromagnetic. Magnetic properties (M-H loops) shows, a weak ferromagnetic behaviour with antiferromagnetic ordering at RT. At RT, x = 0.0-0.6 the samples exhibits disordered paramagnetic property but weakly coupled with antiferromagnetic domains. But, x = 0.8 and 1.0 samples show antiferromagnetic and they are weakly coupled with paramagnetic domains. The temperature dependent magnetization (M(T)) confirms, the augmentation of Neel temperature (T-N) from 155 K to 350 K on increasing x. Mossbauer spectroscopy confirms superparamagnetic nature with the presence of Fe in 3+ state and on increasing x, the spectra changes from doublet to sextet. The ferroelectric (P-E) study confirms the existence of ferroelectric ordering with leaky behaviour. The reasonable ferroelectric loops with antiferromagnetic properties indicate samples with x = 0.2-0.6 show good magnetoelectric characteristics and may find applications in multiferroics. (C) 2016 Elsevier B.V. All rights reserved

Origin of room temperature weak-ferromagnetism in antiferromagnetic Pb(Fe2/3W1/3)O3 ceramic

We report the origin of room temperature weak ferromagnetic behavior of polycrystalline Pb(Fe2/3W1/3)O-3 (PFW) powder. The structure and magnetic properties of the ceramic powder prepared by a Columbite method were characterized by X-ray and neutron diffraction, Mossbauer spectroscopy and magnetization measurements. Rietveld analysis of diffraction data confirm the formation of single phase PFW, without traces of any parasitic pyrochlore phase. PFW was found to crystallize in the cubic structure at room temperature. The Rietveld refinement of neutron diffraction data measured at room temperature confirmed the G-type antiferromagnetic structure of PFW in our sample. However, along with the antiferromagnetic (AFM) ordering of the Fe spins, we have observed the existence of weak ferromagnetism at room temperature through: (i) a clear opening of hysteresis (M-H) loop, (ii) bifurcation of the field cooled and zero-field cooled susceptibility; supported by Mossbauer spectroscopy results. The P-E loop measurements showed a non-linear slim hysteresis loop at room temperature due to the electronic conduction through the local inhomogeneities in the PFW crystallites and the inter-particle regions. By corroborating all the magnetic measurements, especially the spin glass nature of the sample, with the conduction behavior of the sample, we report here that the observed ferromagnetism originates at these local inhomogeneous regions in the sample, where the Fe-spins are not perfectly aligned antiferromagnetically due to the compositional disordering. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved