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Demonstration of broadband THz absorber based nanostructures of topological insulators.

Root like structured Ni-doped zinc oxide [Zn(1-x)NixO (x = 0.09)] thin films were deposited on a non-conducting glass substrate by indigenously developed spray pyrolysis system at optimized substrate hotness of 573±5 K. Thus obtained Ni-doped ZnO thin films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM). XRD result revealed that Ni-doped ZnO has a polycrystalline nature with a hexagonal wurtzite structure. For pure ZnO and Ni-doped ZnO thin films, the particle sizes were 60.9 and 53.3 nm while lattice strain values were 1.56×10−3 and 1.14×10−3, respectively. The film surface showed characteristic root-like structure as observed by the SEM. It was observed that the Ni-doped ZnO thin films were grown in high density along with more extent of branching as compared to pure ZnO thin films but retained the root-like morphologies, however, the branches were more-thinner and of shorter lengths. AFM analysis showed that the surface grains of the Ni-doped samples are homogeneous with less RMS roughness values compared with the undoped ZnO samples. The photocatalytic activity of the prepared thin films was evaluated by the degradation of methyl orange (MO) dye under UV light irradiation. Pure ZnO and Ni-doped ZnO thin films took 150 min and 100 min to degrade about 60% MO dye, respectively.

Identification of novel materials with enhanced thermoelectric (TE) performance is critical for advancing TE research. In this direction, this is the first report on TE properties of low-cost, nontoxic, and abundant core-shell Cu@Cu2O nanocomposites synthesized using a facile and cheap solution-phase method. They show ultralow thermal conductivity of nearly 10-3 of the copper bulk value, large thermopower of ∼373 μVK-1, and, consequently, a TE figure of merit of 0.16 at 320 K which is larger than those of many of the potential TE materials such as PbTe, SnSe, and SiGe, showing its potential for TE applications. The ultralow thermal conductivity is mainly attributed to the multiscale phonon scattering from intrinsic defects in Cu2O, grain boundaries, lattice-mismatched interface, as well as dissimilar vibrational properties. The large thermopower is associated with a sharp modulation in carrier density of states due to charge transfer between Cu and Cu2O nanoparticles and carrier energy filtering. They are tuned by varying the trioctylphosphine concentration.

The present study is focused on the structural correlation of magneto-electric coupling that exists in polycrystalline TbMnO 3 . The X-ray diffraction patterns are collected at various conditions, which are (1) at 300 K without a magnetic field, (2) at 2 K without magnetic field and (3) at 2 K with 7 Tesla magnetic fields. The structural transition in TbMnO 3 has been observed at 2 K and some lattice modulation after applying the magnetic field at 2 K. The Rietveld refinement of TbMnO 3 confirms the orthorhombic phase with centrosymmetric space group Pnma at 300 K. We have observed that the inversion symmetry breaks at 2 K and the polycrystalline TbMnO 3 has been refined using a non-centrosymmetric orthorhombic space group which can be either Pn2 1 a or P2 1 ma. This structural transition confirms the presence of a ferroelectric phase at 2 K. After the application of 7 Tesla magnetic field, the signature of an incommensurate phase has been observed in polycrystalline TbMnO 3 at 2 K. The DC magnetization behaviour with temperature M(T) and field M(H) reveals the antiferromagnetic behaviour of polycrystalline TbMnO3 below 42 K. We have also measured magneto-dielectric property of polycrystalline TbMnO 3 at the low temperature, which confirms the strong magneto-electric coupling in polycrystalline TbMnO 3 below the transition temperature.

A comparative microstructural study of as sintered and rubbed surfaces of BaTiO3 (BTO) ceramic pellet has been carried out using lab (8 keV Cu-Kα) as well as synchrotron (8–19 keV) based powder x-ray diffraction (XRD) at room temperature. These studies show a drastic change in the surface-microstructure of the BTO ceramics. Just a minutes rubbing of the BTO ceramics on a rough surface causes broadening of diffraction peaks. Nearly 3-times increase in the peak width and ∼ 3-times increase in integrated peak intensity of (00l) type peaks has been observed. The changes were analyzed as rubbing induced (00l) texturing and occurrence of anisotropic strain with maxima along [00l]. High temperature XRD studies reveal that for the strained BTO grains, the tetragonal to cubic transformation does not initiates at the proper TC ∼120 °C and does not complete even at temperatures ∼ 350 °C, which is ∼ 3 times the normal TC. About 20% of the tetragonal phase still remains untransformed. These features have been attributed to the formation of strain-glass phase at the rubbed surface of the BTO ceramics.

Ni43Mn47Sn11 and Ni43Mn47Sn10.5B0.5 polycrystalline alloys have been prepared by using arc-melting and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), magnetization measurements and microhardness tests. Temperature dependent XRD measurements shows the evolution of monoclinic martensite phase (P12/m1) from the cubic austenite L21 (Fm-3m) phase. An enhancement (73 K) in the martensite transition temperature from 210 K for Ni43Mn47Sn11 to 283 K for Ni43Mn47Sn10.5B0.5 was observed by DSC measurements, which is attributed to the increase in cell volume on the account of B doping. Microhardness measurements showed that the hardness reduces with B doping in Ni43Mn47Sn11 alloy. The magnetic entropy change evaluated from the magnetization measurements was found to be 14 J/kg-K and 17 J/kg-K for Ni43Mn47Sn11 and Ni43Mn47Sn10.5B0.5 alloys respectively. The effective magnetic refrigeration capacity at a maximum field of 5 T was found to be 94 J/kg for Ni43Mn47Sn11 and 55 J/kg for Ni43Mn47Sn10.5B0.5, suggesting that these alloys have potential for magnetocaloric applications (magnetic refrigeration).

In this work, we present a detailed magneto-optical Kerr effect (MOKE) study of amorphous FeCoB (FCB)/MgO bilayer grown on Si (100) substrate. Two regions with different boron density has been identified in single FCB layer in the as-deposited bilayer due to boron diffusion from FCB to MgO layer at the interface: (i) a boron-deficient layer near FCB/MgO interface (FCBi) and (ii) bulk FeCoB layer (FCBb) located farther away from FCB/MgO interface and having comparatively high boron concentration. As a result, a stress-induced uniaxial magnetic anisotropy is observed in the boron deficient FCBi layer, which is found to be superimposed with the magnetization of FCBb layer. Depending on the angle between the applied magnetic field and the uniaxial easy axis of the FCBi layer, magnetization reversal with single step or double step are observed. Role of interlayer exchange coupling between FCBi and FCBb layer is determined by separating out their magnetic contributions by fitting hysteresis loops with a mathematical function. The disappearance of double step behavior after in-situ annealing up to 473 K, suggests that the observed magnetic anisotropy mainly originates from the strain in the film.

Structural and magnetic phase-transitions in La1-xSrxMnO3+δ (x = 0.67 & 0.71) have been studied employing x-ray diffraction, neutron diffraction and transmission electron microscopy (TEM) in conjunction with electrical-transport and magnetic studies. These studies reveal a cubic to incommensurate (IC) charge-ordered (CO) tetragonal phase-transition in both the samples with k-vector varying with temperature and thus indicates charge density wave-like nature. Followed by magnetic transition from paramagnetic phase to incommensurate antiferromagnetic phase. The nearly equal expansion of the a,b axes in the ab plane and the contraction of the c-axis (i.e. type-I Jahn-Teller distortion (JTD)) indicate that the CO is accompanied by a planer ferro-ordering of 3 d x 2 − y 2 orbitals in the ab plan, which is different from haring-bone type ordering of 3 d 3 x 2 − r 2 / 3 d 3 y 2 − r 2 orbitals, commonly observed in narrow bandwidth CO manganites. For x = 0.71, a second phase-transition from type-I JTD-CO phase (c a) was observed. Through EDAX analysis in TEM, a nano-scale marginal composition difference has been observed to lead to nanoscale phase-coexistence. These studies have revealed first microscopic evidence of CO and nano-scale multiphase coexistence in La1-xSrxMnO3-δ with x = 0.67 & 0.71.

Rare-earth chromates have always been of interest due to temperature-induced magnetization reversal and spin-reorientation phase transitions (SRPTs). In orthochromates containing magnetic rare earths, the spin configuration is supposed to undergo a characteristic changeover across the SRPT followed by an independent ordering of rare-earth moments leading to polar order. However, due to the presence of nearly 14% of highly neutron-absorbing isotope $^{149}\mathrm{Sm}$ in natural Sm based compounds, correct magnetic structure determination of ${\mathrm{SmCrO}}_{3}$ through neutron diffraction measurements has been a challenge. In the present study we investigate the pre- and post-SRPT spin configurations in well characterized ${\mathrm{SmCrO}}_{3}$ through time of flight neutron diffraction measurements carried out in zero field at the high-resolution high-flux WISH beam line of ISIS, in the United Kingdom. Magnetization measurement shows a canted antiferromagnetic phase transition at ${T}_{N1}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, giving rise to a weak ferromagnetism, which undergoes a SRPT at 37 K. Rietveld analysis of the neutron powder diffraction data shows that below ${T}_{N1}=192\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ the ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ moments order in a $P{b}^{\ensuremath{'}}{n}^{\ensuremath{'}}m$:${\mathrm{\ensuremath{\Gamma}}}_{4}$(${\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R}$) spin configuration with their tiny ferromagnetic components ${F}_{Z}$ and $\phantom{\rule{0.28em}{0ex}}{F}_{Z}^{R},$ giving rise to weak ferromagnetism. Below 37 K the $P{b}^{\ensuremath{'}}{n}^{\ensuremath{'}}m$:${\mathrm{\ensuremath{\Gamma}}}_{4}$(${\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R}$) configuration transforms to $Pb{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{2}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}}$) as a result of continuous rotation of ${\mathrm{Cr}}^{3+}$ moments, while approaching SRPT below ${T}_{N1}$. At still lower temperatures the $Pb{n}^{\ensuremath{'}}{m}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{2}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}}$) phase transforms to polar phases, either the $P{2}_{1}^{\ensuremath{'}}{2}_{1}^{\ensuremath{'}}{2}_{1}:{\mathrm{\ensuremath{\Gamma}}}_{26}$(${C}_{x},{\mathbit{G}}_{\mathbit{y}},{F}_{z};{\mathbit{C}}_{\mathbit{x}}^{\mathbit{R}},\phantom{\rule{0.16em}{0ex}}{A}_{y}^{R},\phantom{\rule{0.16em}{0ex}}{F}_{z}^{R}$) or the $P{n}^{\ensuremath{'}}a{2}_{1}^{\ensuremath{'}}:{\mathrm{\ensuremath{\Gamma}}}_{27}$(${F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{z}};{F}_{x}^{R},\phantom{\rule{0.16em}{0ex}}{\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}},{G}_{z}^{R}$) phase, as a result of independent antiferromagnetic ordering of ${\mathrm{Sm}}^{3+}$ moments at ${T}_{N2}l4\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ through ${\mathrm{Sm}}^{3+}\text{\ensuremath{-}}{\mathrm{Sm}}^{3+}$ direct interaction. Our result of the transformation of ${\mathrm{SmCrO}}_{3}$ from ${\mathrm{\ensuremath{\Gamma}}}_{4}$ to ${\mathrm{\ensuremath{\Gamma}}}_{2}$ below SRPT is in contradiction with the ${\mathrm{\ensuremath{\Gamma}}}_{1}$(${A}_{x},{\mathbit{G}}_{\mathbit{y}},{C}_{Z};{C}_{z}^{R}$) spin configuration as reported in Tripathi et al. [Phys. Rev. B 96, 174421 (2017)]. This issue has been independently settled through ground-state energy calculation using spin-dependent density functional theory confirming the ${\mathrm{\ensuremath{\Gamma}}}_{2}$ spin configuration to be of lower energy as compared to that of the ${\mathrm{\ensuremath{\Gamma}}}_{1}$. The role of magnetocrystalline anisotropy in the occurrence of SRPT has been discussed.

The origin of ferroelectricity in the cubic phase of BaTi

A hydrothermal synthesis method was employed for the preparation of tin sulfide (α-SnS) microrod samples (SnS-A and SnS-B) using ethylenediamine and deionized water as the surfactant at ratios from 50 : 50 to 100 : 00. The atomic structures of the α-SnS microrods were studied using atomic pair distribution function (PDF) analysis and total synchrotron X-ray scattering data. The synchrotron X-ray diffraction (ScXRD) patterns and PDF data reveal that the structure of the SnS microrods is orthorhombic. From the refinement of the PDF, the first and second peaks correspond to nearest (Sn2+–S2−) and second nearest distances (Sn2+–Sn2+) of 2.546 (0.003) A and 4.106 (0.004) A, and 2.527 (0.005) A and 4.087 (0.006) A for SnS-A and SnS-B samples, respectively. The TEM results show that samples SnS-A and SnS-B have a microrod structure, with microrod diameters of 800 nm and 500 nm with lengths of tens of micrometers, respectively. The SnS-A and SnS-B samples show a direct band gap of 1.6 eV and 2 eV, respectively, using the Kubelka–Munk transformation of the UV-visible spectra. The micro-Raman spectra of the SnS-A and SnS-B microrods exhibited an Ag mode of SnS at 228.4 and 223 cm−1, respectively. The second peaks at 306.7, and 309 cm−1 are associated with the secondary phases of the SnS2 phase, whereas the third broad peaks at 616.5, and 613 cm−1 revealed that there was a deformation mode of sulfate in the SnS-A and SnS-B samples.

The layered Perovskite compounds play important role in solid state physics due to their intriguing physical properties. We have investigated the structural, complex dielectric and impedance properties of layered perovskite compound YBaCuFeO5(YBCFO). The YBCFO crystallizes in a non-centrosymmetric crystal structure with space group P4mm. The frequency dependent dielectric permittivity (e’) shows two relaxation peaks. Both peaks shift towards higher frequency with increasing temperature and follow Arrhenius behaviour with activation energies 0.24 and 0.13 eV respectively. The Nyquist plot resolves the contributionsfrom grain and grain boundaries. The grain boundary contribution dominates at higher temperatures whereas at lower temperature only grain contribution remains. The dielectric measurement combined with Nyquist plots shows that first relaxing peak arises due to grain contribution and hence represents the materials property, whereas the second peaks arises out of grain-boundary contribution.

Large magnetoresistive materials are of immense interest for a number of spintronic applications by developing high density magnetic memory devices, magnetic sensors and magnetic switches. Colossal magnetoresistance, for which resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external magnetic field, occurs mainly in phase separated oxide materials, namely manganites, due to the phase competition between the ferromagnetic metallic and the antiferromagnetic insulating regions. Can one further enhance the magnetoresistance by tuning the volume fraction of the two phases? In this work, we report a huge colossal magnetoresistance along with the ultra-sharp metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$ manganite compound by suitably tuning the volume fraction of the competing phases. The obtained magnetoresistance value at 10 K is as large as $\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90 kOe external magnetic field and is several orders of magnitude higher than any other observed magnetoresistance value reported so far. Using model Hamiltonian calculations we have shown that the inhomogeneous disorder, deduced from tunneling electron microscopy, suppresses the CE-type phase and seeds the ferromagnetic metal in an external magnetic field., NPG Asia Materials (accepted on 13th June 2018)

Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm−1 at 10 μA cm−2), a low threshold field (0.41 V μm−1 at 100 μA cm−2) and a high field emission current density (7.71 mA cm−2 at 0.78 V μm−1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources.

High resolution x-ray diffraction, strain gauge and Raman spectroscopy measurements of Ca2FeAlO5 as a function of temperature is reported, which provides the evidence of negative thermal expansion (NTE) and strong spin-lattice coupling in this compound. The unit cell showed a decrease in volume with increase in temperature with a distinct jump around 70 °C which corroborates with the magnetic ordering temperature and showed a contraction under magnetic field. The Raman spectra showed variation under magnetic field supporting spin-lattice coupling at room temperature. Most importantly, the NTE (β ≅ − 6.41 × 10−5 °C−1) is observed from room temperature up to ∼70 °C making it very attractive for applications.

Here, we tried to ensure the accurate landscape of ceria QDs surface chemistry using soft X-ray absorption spectroscopy (SXAS) based on insight into the clear-cut electronic structure analyses. From the perspective of molecular orbital (MO) energy level diagram, final state electronic transition of Ce3+ in Oh field has been observed using X-ray absorption near edge region enclosing Ce, MIV-3d3/2 and MV-3d5/2 edges. Information about subtle surface distortion owing to the adsorption of ACTP anchoring group in facilitating efficient charge transfer on the ceria defect site has been qualitatively enlightened by invoking the concept of coordination chemistry. The proximity of the description was further implemented by qualitative analysis of O K-edge X-ray absorption near edge structure (XANES) spectra. Conversely, an increase in O 2p-to-Ce 5d-eg and 5d-t2g surface hybridization via essential oxygen-to-organic ligand interfacial charge transfer was found to be the reason for altered the coordination environment of Ce, provide a shred of direct evidence for the influence of ACTP on CeO2 QD surface. This perspective makes the sense of how recent SXAS technique helps to uncover the complex surface chemistry of ACTP capped CeO2 QDs and affords valuable insight into the specific coordination environment through ligand-to-ligand charge transfer.

Synthesis, formation, structural phase transition, dielectric and magnetic properties of polycrystalline Ba 0.90 Mn 0.10 TiO 3 (BMTO) ceramic have been investigated to study the effect of magnetic ion (Mn) doping at Ba-site in the well-known ferroelectric (FE) material BaTiO 3 (BTO). The polycrystalline ceramic BMTO has been prepared via solid state reaction route. The Wyckoff-site occupancy of the substituted Mn has been determined through x-ray diffraction (XRD) and soft X-ray absorption measurement via confirmation of its oxidation state to be 2+ and that of Ti to be 4+. The temperature dependent XRD, dielectric and pyroelectric studies show all the known transitions similar to the pristine BTO. However, the transition temperatures (T c ) were found shifted towards lower temperatures as compare to the pristine BTO. The shifts in T c corresponding to cubic-tetragonal and tetragonal-orthorhombic transitions are significant as compared to that of orthorhombic-rhombohedral transition. Frequency dependent dielectric measurements show the space-charge related dielectric relaxation. The dc-magnetization measurements show antiferromagnetic interactions in BMTO. Our results also address the role of Ba site on the ferroelectric properties of BTO.

The temperature dependent structural, transport and magnetic properties of Pr 0.20 Sr 0.80 Mn 1− x Mo x O 3−δ ( x = 0.0, 0.02, 0.04 and 0.10) have been studied using low-temperature x-ray and electron diffraction, resistivity and dc magnetization measurements. Unlike the undoped ( x = 0) sample, which is cubic at room temperature, the Mo doped samples show phase coexistence of cubic ( P m 3 ¯ m ) and tetragonal ( I 4 / m c m ; c / 2 > a ) phases. The Mo doping stabilizes the tetragonal ( I 4 / m c m ) phase in the temperature range of 300–330 K. The tetragonality of the sample for x = 0.10 however appears to be of different kind, which further under goes an additional transition from tetragonal to orthorhombic ( F m m m ) phase below 200 K. Transmission electron microscopy, employing electron-diffraction and high-resolution micro-structural imaging, clearly reveals the occurrence of charge-ordering (CO) for x = 0.04 and 0.10 samples with non-integral modulation along [110] type perovskite direction. The dc magnetization and resistivity data very well correlate with the observed structural and associated CO antiferromagnetic phase transitions. The increased stability of the distorted perovskite phases and the occurrence of CO are found to correlate with the increase in the Mn 3+ /Mn 4+ ratio as a function of Mo 6+ substitution. The possible role of effective B-site cation size in stabilizing the distorted perovskite phase has been discussed in terms of tolerance factor.

The phase diagram of La 0.25 Sr 0.75 MnO 3.01 has been investigated by performing temperature dependent powder x-ray diffraction, transmission electron microscopy (TEM), and resistivity and magnetization measurements. It undergoes competing structural phase-transitions from charge disordered cubic to charge-ordered (CO) tetragonal phase having compressed Jahn-Teller (JT) distorted octahedra (c/a 1) at ∼250 K. The three phases coexist from 250 to 210 K. The nano-scale (10–20 nm) coexistence of CO and twin tetragonal phases sustains down to 80 K, with twin tetragonal phase fraction increasing substantially on cooling below 210 K. In TEM diffraction data, the CO phase shows well defined super-lattice spots with ∼8x8-fold CO modulation along [110] type direction of the perovskite lattice and typical CO micro-structure with lattice fringes. The twin microstructure resulting in twin spots can also be observed for the elongated JT-distorted tetragonal phase. The compressed and elongated distortions of the octahedra for CO and twin tetragonal phases implies ferro orbital-ordering of 3d x 2 -y 2 and 3d 3z 2 -r 2 orbitals in the ab -plane and along c -axis, respectively. During heating, the twin tetragonal to CO phase transformation was fully reversible with a wide hysteresis and the CO modulation was found to flip its direction from [110] to [10 1 ¯ ] & [01 1 ¯ ] in the same domain. Thus, our results reveal the nano-scale structural phase separation due to competitive nature of CO and twin phase over wide temperature range.

In this paper, we have presented the effect of swift heavy ion beam irradiation on the structural, microstructural, electrical and magnetic properties of Sn 0.9 Mn 0.1 O 2 thin films. The structural and electrical results have been interpreted by using properties of native or point defects, whereas the magnetic and morphological variations have been explained in terms of the conductivity of material. Efforts have been made to summarize the properties of all possible charged and neutral point defects ( V Sn 4 - , Sn i 4 + , V O 0 , O i 2 - , Sn O 4 + , O Sn 2 - , H O + ) and afterwards from the correlation between experimentally-observed and theoretically-calculated results various interesting conclusions have been drawn.

The influence of magnetic field on the crystal structure of colossal magnetoresistance (CMR) material La0.5Sr0.5MnO3+delta has been investigated. Low temperature high-magnetic field powder X-ray diffraction (XRD) measurements were carried out on La0.5Sr0.5MnO3+delta in temperature range from 4.2 to 300 K and magnetic field range from 0 to 8 T. A first order structural phase transition from tetragonal I4/mcm to orthorhombic Fmmm phase, coupled with reported electronic and magnetic phase transition from ferromagnetic metal to antiferromagnetic insulator state has been started at similar to 200 K and completed at similar to 100 K. On the application of 8 T magnetic field this magneto-structural phase transition shifted to lower temperature (similar to 162 K) with phase coexistence regime down to 4.2 K. Isothermal X-ray diffraction measurements at 150 K infer the evidence of magnetic field driven first order structural phase transition from Fmmm to I4/mcm. These results consistent with the resistivity and magnetoresistance results; present the microscopic evidence of strong spin-lattice coupling and reveal the magnetic field driven structural phase transition as the origin of observed colossal magnetoresistance in this material. (C) 2016 Published by Elsevier B.V.

Structural, dielectric and ferroelectric measurements of polycrystalline BaTi 1 − x Sn x O 3 (x=15%) are reported. Detailed temperature dependent dielectric, x-ray diffraction and ferroelectric loop (P-E) measurements indicate the sequence of paraelectric and phase coexistence (ferroelectric and relaxor) phase as a function of lowering temperature. Hysteresis behavior observed in maximum polarization is envisaged as the signature of disorder induced first order phase transition in the phase co-existence region. The evidence for the possibility of tuning phase fraction in the phase co-existence region with electric field as a variable similar to that of magnetic materials with magnetic field is reported.

Single phase polycrystalline sample of perovskite SrTi0.5Mn0.5O3 (STMO) has been successfully synthesized via solid state reaction route. Its detailed structural and physical properties have been studied using powder x-ray diffraction (XRD), transmission electron microscopy (TEM), magnetization, specific heat, and dielectric measurements. Rietveld analysis of the powder XRD data and TEM studies confirm that STMO is a disordered perovskite with Pm-3m space group in which titanium and manganese ions are randomly distributed at the 1b site. The dc magnetization (χdc-vs-T) measurements in the temperature range 2–300 K reveal a single anomaly at ∼13 K with predominant long range canted antiferromagnetic (AFM) ordering. The frequency invariant maximum at 13 K in the ac susceptibility (χac-vs-T) data discards the spin-glass behavior. Despite the presence of sharp feature in magnetization data, the specific heat data (Cp-vs-T) shows only a broad hump around 13 K, which has been attributed to the magneto-structural ordering giving rise to canted AFM state in chemically disorder STMO. Matching with the magnetic and specific heat anomaly, the dielectric permittivity also shows a broad anomaly around 13 K, indicating the possible magneto-dielectric coupling in STMO system.

The temperature dependent neutron powder diffraction (NPD) and magnetization measurements of vanadium based garnet Ca 5 Ni 4 V 6 O 24 (CNVO) have been performed to explore its crystal and magnetic structures. The magnetization results illustrate two magnetic anomalies at 7 and 4 K. The Rietveld analysis of room temperature x-ray diffraction and NPD data confirms its Ia -3 d crystal structure. The temperature dependent NPD shows the emergence of magnetic reflections below 7 K whose intensity keeps on increasing with decreasing temperature down to 1.5 K. The crystal structure remains cubic down to 1.5 K. Rietveld analysis reveals that below 7 K, the Ni moments in CNVO undergo a commensurate collinear A-type antiferromagnetic ordering with propagation vector k =(0,0,0) and the per site ordered moment of Ni 2+ is 1.69±0.05 μ B . Absence of any additional magnetic or nuclear reflections below 4 K confirms that the nuclear and magnetic structures remain invariant across the 4 K magnetic anomaly.

PbS/polyvinylpyrrolidone (PVP) nanocomposite films with tunable band gap are synthesized by solid state in situ thermolysis. Precursor films are dip-coated on glass substrates from a methanolic solution of Pb2+–thiourea complex and PVP and then heated in air at 110 °C for 10 minutes to obtain shiny brown clear films of PbS/PVP. The formation of PbS nanoparticles in PVP matrix is confirmed by X-ray diffraction studies. The size of PbS nanoparticles varied from 2 to 8 nm depending of the weight fraction of the Pb2+–thiourea complex in the PVP. Transmission electron microscopy shows that the nanoparticles are spherical. The transmission spectra of the PbS/PVP films in the wavelength range of 300 to 2600 nm showed absorption edges near 900 nm and below due to the presence of PbS nanoparticles. The band gaps of PbS/PVP films, as determined from Tauc plots, varied from 0.8 to 1.92 eV as the weight fraction of the complex decreased from 82 to 36%. Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and 13C Nuclear Magnetic Resonance (NMR) studies reveal that there is strong interaction between PbS and PVP which limits the growth of the nanoparticles.

We have studied the partially ordered double perovskite (PODP) and spin-glass phase in $\mathrm{Sr}(\mathrm{M}{\mathrm{n}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}){\mathrm{O}}_{3}$ ($x=0.20$ to 0.40) using neutron powder diffraction (NPD), muon spin relaxation (\ensuremath{\mu}SR), magnetic susceptibility (\ensuremath{\chi}), and x-ray photoelectron spectroscopy measurements. Structural studies reveal that $\mathrm{SrM}{\mathrm{n}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}{\mathrm{O}}_{3}$ undergoes a quasicontinuous transformation from simple perovskite ($Pm\ensuremath{-}3m$) to PODP ($P{2}_{1}/n$) phase as $x$ increases. ${\ensuremath{\chi}}_{\mathrm{dc}}(T)$ and ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$ measurements show a sharp cusplike peak at spin-glass transition ${T}_{g}$. The muon relaxation rate (\ensuremath{\lambda}) peaks at ${T}_{g}$ following a critical growth, given by $\ensuremath{\lambda}=\ensuremath{\lambda}(0){\ensuremath{\tau}}^{\ensuremath{-}w}[\ensuremath{\tau}=(T\ensuremath{-}{T}_{g})/{T}_{g}]$. No long-range magnetic order is observed in NPD below ${T}_{g}$. These measurements confirm a tunable spin-glass state of $\mathrm{SrM}{\mathrm{n}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}{\mathrm{O}}_{3}$ for $0.2lxl0.4$. The spin-glass phase appears with the onset of $\mathrm{M}{\mathrm{n}}^{2+}$ cations, which induce competing ferro-antiferro interactions leading to exchange frustration. The ${T}_{g}$ decreases as the W content and $\mathrm{M}{\mathrm{n}}^{2+}$ concentration increase. Our results suggest that the spin-glass phase can be tuned through the relative concentration of 2+, 3+, and 4+ Mn ions.

The present work reports the magnetodielectric (MD), ferroelectric, magnetoelectric (ME), low-temperature (LT) Raman, low-temperature high magnetic field (LTHM) $^{57}\mathrm{Fe}$ M\"ossbauer and x-ray diffraction (XRD) studies of polycrystalline multiferroic ${\mathrm{GdFeO}}_{3}$. Ferroelectric ordering as a result of magnetic ordering of ${\mathrm{Gd}}^{3+}$ ions (${T}_{N,\mathrm{Gd}}$) is confirmed from the pyrocurrent measurements carried out in conventional and bias-electric field protocols. Coupling between magnetic and electric orderings, viz., magneto-electric (ME) coupling, is confirmed by measuring the dielectric constant and pyrocurrent in the presence of magnetic field. A huge magnetodielectric (MD) coefficient ($\ensuremath{\approx}\ensuremath{-}12%$) is observed below the ${\mathrm{Gd}}^{3+}$ ordering temperature, reaching a saturation value with a field of about 3 Tesla. From LT Raman data across ${T}_{N,\mathrm{Gd}}$, the presence of spin-phonon coupling and the development of new modes indicating the symmetry reduction are observed. The average displacement of cations obtained from LTHM XRD measurement corroborates the ferroelectric polarization measurements. Signatures of a transferred hyperfine field are observed from LTHM $^{57}\mathrm{Fe}$ M\"ossbauer data. The variation of the effective internal magnetic field obtained from in-field M\"ossbauer data gives evidence for the predicted spin structures of ${\mathrm{GdFeO}}_{3}$ with magnetic fields below ${T}_{N,\mathrm{Gd}}$. The observed anomalous variation of the center shift and resonance area from $^{57}\mathrm{Fe}$ M\"ossbauer data across ${T}_{N,\mathrm{Gd}}$ ordering is explained in terms of phonon mode softening. Observed MD and ME effects are explained in terms of spin-phonon coupling as evidenced from LTHM $^{57}\mathrm{Fe}$ M\"ossbauer and LT Raman data.

Effect on structural phase-transition and dielectric-relaxation behaviourof very minor substitution (2%) of Sr, at the Ba-site of the morphotropic phase boundary composition 50/50 BCT/BZT, has been studied employing XRD and frequency dependent dielectric (e’r-T) measurementsin the range of 90-420K. XRD studies show the known phase-transition sequence but with a highly diffused phase boundaries. The e’r-Tshows a non-dispersing and non-reversibleer maxima at ∼ 303K with a hysteresis ranging from 90 K to 380 K. Anomalously the e’r-Tabove320K showsa relaxor-like frequency dispersion(10Hz-10kHz) existing prior to tetragonal-cubic phase-transition. This observation shows co-existence of the relaxor and normal ferroelectric phases.Effect on structural phase-transition and dielectric-relaxation behaviourof very minor substitution (2%) of Sr, at the Ba-site of the morphotropic phase boundary composition 50/50 BCT/BZT, has been studied employing XRD and frequency dependent dielectric (e’r-T) measurementsin the range of 90-420K. XRD studies show the known phase-transition sequence but with a highly diffused phase boundaries. The e’r-Tshows a non-dispersing and non-reversibleer maxima at ∼ 303K with a hysteresis ranging from 90 K to 380 K. Anomalously the e’r-Tabove320K showsa relaxor-like frequency dispersion(10Hz-10kHz) existing prior to tetragonal-cubic phase-transition. This observation shows co-existence of the relaxor and normal ferroelectric phases.

The origin of ferroelectricity in the cubic phase of BaTi1−x Hf x O3 has been investigated. The presence of well-defined ferroelectric polarization versus electric field (PE) hysteresis loop in the samples with global cubic symmetry suggests the presence of ‘local polar regions’, induced possibly due to the huge difference in the electronegativity and also difference in the ionic radii of Hf+4 and Ti+4 ions, which may lead to local structural disorder. The presence of polar regions is also supported through the appearance of A1(TO) polar mode in Raman spectra which in principle should be absent in the samples with cubic symmetry. The results are discussed in terms of disorder-induced local dipoles due to the electronegativity difference between Hf and Ti ions.

Ceramic sample of CuCrO2 was synthesized via a solid-state reaction method. XANES, dielectric, ferroelectric, pyroelectric, synchrotron x-ray diffraction (SXRD), transmission electron microscope (TEM) and Raman measurements were performed on the prepared sample. Ferroelectric hysteresis loop, PUND, and pyroelectric current measurements indicate the presence of ferroelectricity in the prepared sample. The appearance of a broad maximum in dielectric permittivity and its frequency dispersion indicates the possibility of relaxor-type ferroelectricity in the system. Furthermore, TEM measurements revealed the presence of nano regions that are speculated to be polar and hence are giving rise to relaxor-type ferroelectricity. Careful analysis of XRD data indicates that the distorted CrO6 octahedra is giving rise to strain in the sample. This strain might be responsible for the observed nano regions, which might be polar, in the otherwise non-polar matrix. It is proposed that these polar regions are responsible for the presence of relaxor-type ferroelectricity in the sample.

Manufacturing quantum dots (QDs) and their suspensions through incorporation of surface coatings can have enormous attention in manipulating surface properties such as size, shape, and structure. The surface of engineered QDs capped by the adsorption of organic matter is known for strongly influencing their physicochemical properties, which is very useful for many biomedical and technological applications. Prerequisite for any possible applications, the effect of organic matter on the surface of nanoparticles is important. In this contribution, owing to the privileged medicinal scaffolds based on the structure of pyridine derivatives, we have synthesized cerium oxide QDs with ∼2.4 nm in size capped with anionic-rich head groups of 2-amino-3-chloro-5-trifluoromethylpyridine (ACTP), and the assay is based on the steric stabilizing capping behavior of anionic-rich ACTP molecules on the surface of CeO2 QDs. Aggregated QDs, obtained by adding capping agent in the reaction, have been characterized by powder X-r...

We have investigated the complex dielectric and impedance properties of magnetoelectric compound Fe2TiO5 (FTO) as a function of temperature (T) and frequency (f) to understand the grain (G) and grain boundary (Gb) contributions to its dielectric response. The temperature and frequency dependent dielectric permittivity data shows a sharp increase in permittivity above 200K accompanied with a frequency dependent peak in loss. At T less than 175K, only G contribution dominates even at lower frequency (nearly 100Hz), but for T greater than 175K, the Gb contribution starts appearing at low frequency. The value of critical frequency distinguishing these two contributions increases with increasing temperature. The observed non-Debye dielectric relaxation follows thermally activated process and is attributed to polaron hopping. Further the frequency dependence of ac conductivity follows the Jonscher power-law. The temperature dependency of critical exponent s shows that the correlated barrier hopping model is appropriate to define the conductivity mechanism of FTO in the studied temperature regime., 16 pages, 6 figures, Accepted in Journal of alloys and compounds

This present investigation deals with the synthesis of Fe doped ZnO nanocrystals by chemical method of microwave irradiation technique and the special attention is given to structural, optical and magnetic behavior. The X-ray diffraction analysis confirmed the single phase ZnO wurtzite structure without any impurity or secondary phase formation. The shifting of [1 0 1] peak in the higher angle side is due to the smaller cation of Fe 3+ than Zn leads to the change in lattice parameters. The formation of metal oxide bond at 450 cm −1 is confirmed by Fourier transform infrared spectrum and the Raman modes ∼324 cm −1 , 432 cm −1 and 564 cm −1 correspond to ZnO is identified by micro Raman spectrum. The band gap energy of the samples increases with the increase of Fe concentration due to the increase of crystal size. The ZFC–FC curve confirms the absence of Curie temperature below 350 K. The room temperature magnetization measurement shows the paramagnetic behavior in all samples.

The atomic structures of polymorphs of Zn–S nanocubes and nanowires have been studied using atomic pair distribution function (PDF) analysis and total synchrotron X-ray scattering data. The PDF of sample S1 shows face centered cubic packing and sample S2 shows a hexagonal closed packed structure. Phase transformations were observed with homogenous and nonhomogeneous treatment of temperature. Samples were synthesized by a hydrothermal method. PDF suggested a cation–cation (Zn2+–Zn2+) distance for S1 and S2 at 3.85 A with coordination numbers ∼1 and ∼4, respectively. The core structure of a cubic ZnS nanostructure with extensive stacking faults was confirmed by TEM. The diameters of the samples were extracted using PDF data which are in good agreement with the TEM results. The FE-SEM and TEM results show that samples S1 and S2 have nanocube and nanowire-like structures, respectively. The interatomic distance was calculated by considering the PDF analysis. The energy band gap of the samples was estimated using UV-Vis spectra. It was observed that the energy band gap goes on decreasing during the structural transformation from cubic to wurtzite structure.

Microstructure, ferroelectric and dielectric properties investigation reveals non-stoichiometric chemical ordered regions (CORs) and relaxor like dielectric characteristics in 800 °C to 1200 °C uniaxially hot pressed (HP) lead magnesium niobate (PMN) ceramics. Occurance of (½½½) superlattice reflections along 〈1 1 1〉 in 〈1 1 0〉 zone axis SAED pattern and the presence of bright nano-meter regions in corresponding dark-field images in 800 °C hot pressed PMN (HP800) demonstrates the formation of the CORs as soon as the perovskite phase is formed during calcination at 800 °C. The lattice constant is observed to remain constant with HP sintering temperature. An increase in dielectric constant maximum (em) from 8800 to 25,000 and shift of temperature of the em (Tm) from 278 K to 263 K is explained considering a restriction of thermal activity of large polar regions near to the grain boundaires of smaller grains.

Comparative study of the effects of substitution (25%) of Jahn-Teller (JT) active Cu2+ and non JT active Mn2+ cations, at the Ni2+ site, on the geometric frustration (GF) and cooperative JT distortion (CJTD) in multiferroic NiCr2O4 has been carried out with the help of low-temperature magnetization, x-ray diffraction and time of flight (TOF) neutron powder diffraction (NPD) measurements. On Mn2+ substitution the CJTD, which causes elongation of the NiO4 tetrahedra in I41/amd phase of NiCr2O4, gets suppressed at room-temperature (RT) and stabilizes the Fd-3m phase in (Ni0.75Mn0.25)Cr2O4. On the contrary the Cu2+ substitution inverts the effect of CJTD and the tetrahedra get flattened at RT, which in turn oppositely distorts the I41/amd lattice in Ni0.75Cu0.25Cr2O4. The frustration index decreases on substitution. Intriguingly, the tetragonal to orthorhombic phase transition and the antiferromagnetic ordering, which are clearly evident in the pristine NiCr2O4 and the Cu2+ substituted sample respectively at 30 K and 70 K, have not been observed for the Mn2+ substituted sample. This has been attributed to the change in Cr3+- Cr3+ direct magnetic-interaction on structural transition. However, the long-range ferrimagnetic order remains intact for all the three compositions i.e. NiCr2O4, Ni0.75Mn0.25Cr2O4 and Ni0.75Cu0.25Cr2O4 occurring at 75 K, 70 K and 95 K, respectively. The Mn2+ substituted compound shows short-range magnetic correlation at low-temperatures, as evident from the diffuse and broad hump in the intensity-vs-d spacing plot of TOF NPD data. This short-range magnetic order has been attributed to the known spiral magnetic order.

In this work, the effect of graphene nanoplatelets (GNPs) on the physico-mechnaical properties of short carbon fiber (SCF) reinforced polyamide 66/thermoplastic copolyester elastomer composites was investigated. The composites were fabricated with extrusion followed by injection molding method. The host matrix, fiber plus host matrix and graphene nanoplatelets loaded hybrid composites were examined for density, hardness, tensile, flexural and impact properties according to the governing ASTM standard. Fiber reinforcement decreased void content to < 1 % but GNPs were able to keep void content under limits. Hardness and impact strength augmented with 2 wt. % graphene nanoplatelets loading, owing to superficial dispersion developing the relationship between the hardness and impact strength. Graphene nanoplatelets loading benefitted the tensile property. However, the same has a deteriorating effect on flexural strength. Flexural modulus increases until 2 wt. %. Improvement in mechanical properties upon GNPs loading is very feeble when compared to the enhancement with SCFs loading to the host. Upon comparing the properties, it was observed that 2 wt. % of graphene nanoplatelets performed admirably and was recognized as an optimum filler loading. Morphology of fractured surfaces was studied by analyzing the scanning electron microscope images to understand the various features and mechanisms.

We report the first thermoelectric properties of Cu1−xAgxS, x = 0–0.75 nanocomposites, synthesized by using a facile polyol method. Systematic characterizations using powder XRD, Rietveld refinement of XRD, EDAX, XPS and Raman spectroscopy confirmed their single phase, hexagonal crystal structure with the space group P63/mmc, nominal elemental composition, valence states of the constituent elements and stoichiometric nature. The TEM images showing the CuS formation of nearly perfect hexagonal disk-like particles of average thickness 26.7 nm and breadth ranging in a few hundreds of nanometers with nanorods stacked from these hexagonal nanodisks (NDs) elongated along the c axis corroborate the FESEM images. Attributed to structural phase transition, an anomaly at 55 K is clearly observed in both the thermopower and Hall resistivity data. By increasing x, a systematic reduction in thermal conductivity was observed near 300 K. Consequently, a 50% enhancement in figure of merit was observed for Cu0.9Ag0.1S as compared to pure CuS at 300 K. These results therefore are expected to provide a new direction in improving ZT near 300 K.

This paper reports rapid, continuous and carbon-nanotube free synthesis of carbon encapsulated magnetic nanoparticles by thermal-plasma expansion technique, which combines the typical advantages of high-temperature plasma assisted synthesis method with efficient particle-size control. Core nanocrystals were encapsulated with few layers of graphitized carbon, which could provide protection against both oxidation and intense chemical treatment. The average iron/iron-carbide nanoparticle diameter (7.7, 9 and 10 nm) and the width of the size distribution increased with pressure in the sample collection chamber, as a result of the decreasing quenching rate of the plasma jet. This also resulted in the smaller particles remaining frozen predominantly in the high-temperature γ-Fe phases, part of which was oxidized subsequently and eliminated preferentially during the purification process. All samples could be correlated with smooth variation of magnetic properties; saturation magnetization, remnant magnetization and coercive-field enhancing with increasing chamber pressure or average particle size. The low pressure synthesized sample with smallest average particle size approached super-paramagnetic behavior (saturation magnetization = 51.8 emu/g, ratio of remnant to saturation magnetization = 4.9 and coercive field = 52 Oe), which may be ideal for biomedical applications. High-pressure samples on the other hand have a higher saturation magnetization (76.3 emu/g) and coercive fields (123 Oe).

We report the existence of ferromagnetic correlations (FMC) in the paramagnetic (PM) matrix of cubic La1−xSrxMnO3−δ (x = 0.80, 0.85) well above its coupled structural, magnetic, and electronic phase transitions. The dc-magnetization versus temperature [M(T)] behavior under different magnetic fields (from 100 Oe to 70 kOe) shows the presence of short-range magnetic correlations up to (TFMC ∼) 365 K, far above the antiferromagnetic ordering temperatures (TN =) 260 and 238 K for x = 0.80 and 0.85, respectively. More importantly the observed short-range FMC survive even up to 70 kOe, which indicates their robust nature. The temperature region between TN and TFMC is dominated by the presence of correlated ferromagnetic (FM) entities within the PM matrix and stabilized due to A-site chemical disorder. Our results further illustrate that for the studied compositions, the oxygen off-stoichiometry does not have any significant effect on the nature and strength of these FM entities; however, FM interactions increase in the oxygen-deficient samples. These compositions are the unique examples, where the presence of FMC is observed in an undistorted basic cubic perovskite lattice well above TN and therefore are novel to understand the physics behind the colossal magnetoresistance effect.

Nickel nanoparticles (NPs) of different shapes and sizes in polydispersed as well as monodispersed forms were synthesized using trioctylphosphine (TOP), triphenylphosphine (TPP), oleylamine (OA) and their combinations as surfactants to study their self-assembly inducing capabilities. Randomly agglomerated polydispersed NPs were found for TPP and OA, and TPP or OA separately. However, in consolidation with the earlier report of Singh et al., J. Mater. Chem. C, 2014, 2, 8918, NPs formed using TOP only and a combination of TOP with OA naturally exhibited monodispersed NPs associated with natural nanolattice formation without any other external force or surfactants, demonstrating clearly the self-inducing capacity of TOP into monodispersed NPs and their self-assembled nanolattices. Fourier-transformed infra-red (FTIR) data clearly indicated the capping of these surfactants along with acetylacetonate ligands from nickel acetylacetonate precursor on the surface of the NPs. Remarkably, the narrowest zeta potential (ζ) base-widths were observed for samples possessing a self-assembled nanolattice, compared to the broader ones for randomly agglomerated particles.

Structural and x-ray photoelectron spectroscopic studies have been performed on bulk pellet sample of SrTi0.5Mn0.5O3 to confirm the antisite disorder and charge state of different ions (Ti, O and Mn). The XPS spectra of titanium (Ti) 2p, oxygen (O) 1s and manganese (Mn) 2p core levels have been performed to confirm the multiple charge states of individual ions present in the sample.

Comprehensive X-ray diffraction (XRD) studies have been performed at different temperature (T) (4.2-300 K) and magnetic field (H) (0-8 T) to understand the evolution of crystal structure of Nd0.49Sr0.51MnO3+delta (NSMO) under non ambient conditions. The T dependent XRD results show the abrupt change in the lattice parameters without any change in lattice symmetry at similar to 200 K, which is associated with the first order structural phase transition from ferromagnetic to antiferromagnetic phase. This phase transition is strongly H dependent and shifted to lower temperature (similar to 150 K) on the application of 8 T field with phase coexistence (high temperature phase similar to 18%), even down to 4.2 K. Isothermal XRD results at 150 K under different H clearly illustrate the H induced first order structural phase transition. The critical H at which this phase transformation starts is similar to 1 T, with rapid growth above 4 T with hysteretic nature during increasing and decreasing H. These results are supported with the resistivity and magnetoresistance results and affirm the strong spin-lattice coupling in NSMO. Our detail studies reveal the structural correlations to the observed colossal magnetoresistance and magnetocaloric effect in this material. (C) 2017 Elsevier B.V. All rights reserved.