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Unlike a typical spin–phonon coupling, an exhibition of unconventional spin–phonon coupling, which is mediated via magnetostriction effect, is reported in a hole-doped double perovskite Pr1.5Sr0.5CoMnO6. Various investigations including electronic and crystal structures, spin structure, transport property, lattice dynamics, and theoretical density of states analysis by density-functional theory (DFT) have been performed. A substantial increase in the mean oxidation states of Co ions and a concurrent abrupt decrease in the resistivity upon Sr doping is observed, thus altering its underlying transport mechanism. An insulating and ferromagnetic (FM) ground state is predicted by DFT calculations. The neutron diffraction data analysis reveals a complex crystal structure of Pr1.5Sr0.5CoMnO6, which consists of B-site disordered monoclinic (P21/n) and orthorhombic (Pnma) structures, highlighting the presence of an anti-site disorder in the system. The analysis also suggests an overall FM ordering of Co/Mn spins below 150 K for the monoclinic phase, whereas no such magnetic ordering is found for the orthorhombic phase. More interestingly, the neutron powder diffraction study perceives the presence of a strong magnetostriction effect in the system. Raman spectroscopy unravels the presence of a spin–phonon coupling, which is essentially mediated by the magnetostriction effect. [ABSTRACT FROM AUTHOR]

Significant experimental effort has been explored to search and characterize high-k materials with magnetodielectric effect (MDE) of series of rare earth (RE) oxide (RE2O3) nanoparticles (NPs) embedded in SiO2 glass matrix by a sol-gel route. Properly annealed sol-gel glass (in which RE = Sm, Gd, and Er) shows colossal response of dielectric constant along with diffuse phase transition and MDE around room temperature. The radial distribution functions, reconstructed from extended x-ray absorption fine structure, show the shortening of RE3 + -O depending on the RE2O3 NP size, which is consistent with oxygen vacancy induced dielectric anomaly. The magnetoresistive MDE is very much conditioned by magnetic property of RE2O3 NP grain, the degree of deformation of the lattice and constituent host. [ABSTRACT FROM AUTHOR]

We report multifunctional properties of the charge disproportionate correlated electronic system La0.5Ba0.5FeO3 synthesized by conventional solid state reaction route. The bulk sample undergoes semiconductor-metal like transition at TSM = 102 K showing appreciable magnetoresistance (∼20%) around TSM even at a low field (∼0.5 T). A crossover of electrical conduction mechanism from Mott's variable range hopping to small polaron hopping occurs around 210 K, well above TSM. Analysis of the transport, magnetic susceptibility, and magnetization data in the light of de Gennes proposal indicates the formation of canted antiferromagnetic spin order preceded by charge ordering in La0.5Ba0.5FeO3. Nonsaturation behavior and nonlinearity of the M-H curve at low temperature and at high field (∼5 T), confirms the canted spin order. The observed resistive transition is considered to be associated with the onset of weak ferromagnetic ordering in the canted antiferromagnetic spin state of the materials. Moreover, novel ferroelectric like behavior showing electric field-polarization hysteresis loop below the charge ordering temperature along with anomalous magnetocapacitance response representing magnetoelectric coupling is also observed. In the low temperature regime spin lattice coupling might be responsible for exhibiting magnetocapacitance in La0.5Ba0.5FeO3. Such multifunctional character implies fundamental as well as technological importance of this sample. [ABSTRACT FROM AUTHOR]

Interesting low temperature memory phenomena have been observed from equilibrium and out of equilibrium magnetic measurements on the La0.7Ca0.3MnO3 nanomanganite system. The observed phenomenon were screened for atomic spin glass (SG), super spin glass (SSG), cluster glass (CG), and superparamagnetic behavior. The results evidences of SG like behavior at low temperature (<40 K) in this manganite system consisting of ferromagnetic nanoparticles. In the temperature region between 40 K and the ferromagnetic Curie point TC∼217 K, a ferromagnetic CG state develops with a relatively weaker interparticle interaction than that of the low temperature SG phase. The dynamic magnetization shows aging, chaos and memory effects. Moreover, we have also noticed asymmetric response in magnetic relaxation in response to positive and negative temperature cycling protocols. The origin and nature of the low-temperature SG state in this system is discussed within the framework of hierarchical organization of metastable states. The results show existence of various time and length scales in the system, which can be explained by considering the nanoparticles with grain boundary spin disorder and the presence of noncompact ferromagnetic clusters. [ABSTRACT FROM AUTHOR]

Internal nanodomains in the form of stripe or nanostripe domains (NSDs) have been found in high permittivity CaCu3Ti4O12 (CCTO) prepared by ceramic route. High resolution transmission electron microscopy study detects plane defects along the domain boundaries. Electron diffraction patterns indicate the existence of probable twinning in CCTO, resulting plane defects. X-ray photoelectron spectroscopy studies also detect Cu1+ and Ti3+ demonstrating the presence of compositional disorder in CCTO which leads to lattice dislocations along the domain boundary regions. Highly disordered plane defects are responsible for creation of NSDs and act as insulating barriers. Thus, high permittivity is achieved through internal barrier layer capacitance within CCTO grains. Present observation of NSDs in CCTO and their origin finally confirm the extrinsic mechanism of the huge dielectric response of CCTO ceramic. [ABSTRACT FROM AUTHOR]

Homogeneous thick film (∼0.10 mm) of high dielectric K0.05Ti0.02Ni0.93O; abbreviated as KTNO/polyvinylidene fluoride (PVDF) composite has been prepared by hot-molding technique. The frequency and temperature dependent dielectric behavior of this composite has been studied by varying the KTNO volume fraction (fKTNO). Near the percolation threshold (fKTNO=0.40), a large enhancement of effective dielectric permittivity ([variant_greek_epsilon]eff∼400 which is 40 times higher than that of pure PVDF) with low loss (∼0.20 at 1 kHz) is observed. The experimental [variant_greek_epsilon]eff data have been fitted with different theoretical models and found to follow percolation theory successfully. Such a high [variant_greek_epsilon]eff and low loss flexible dielectric material appears to be suitable for technological applications. [ABSTRACT FROM AUTHOR]

The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO3 (o-HMO) films grown on Nb-doped and undoped SrTiO3(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) has been observed in three well-defined temperature intervals (region I: 2–115 K, region II: around charge order transition TCO, and region III: around room temperature) in polycrystalline Nd0.5Ca0.5MnO3 (NCMO) manganite system showing a first order (CO) transition at a temperature, TCO∼250 K. The magnitude of ΔSM(H) increases monotonically with applied magnetic field but does not reach saturation even at fields as high as 60 kOe. In the three given temperature regions, negligible magnetic and thermal hysteresis are found, which satisfies the requirements of using NCMO as an effective magnetocaloric material for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

We report a low field (H=0.5 T) magnetoresistance of colossal magnetoresistive (CMR) composites prepared with ferromagnetic (FM)—antiferromagnetic (AFM) coupled system (100-x) La0.7Pb0.3MnO3(LPMO)+xPr0.63Ca0.37MnO3 with x=0–85 wt %. A large increase (∼16% maximum) of magnetoresistance (MR) (∼10% for pure LPMO) is observed at a relatively higher optimum concentration (x=70% AFM). Interesting double peaks are observed for lower AFM concentrations (x<=35%) in the resistivity-temperature [ρ(T)] curve: one due to the usual intrinsic double exchange interaction (between Mn3+ and Mn4+) mechanism and the other due to the stronger FM-AFM coupling for lower concentration. Unlike the usual ceramic CMR material, thermoelectric power (TEP) in this system is also nonadditive in character, indicating the presence of additional defects and strain in this composites. A two-channel (conducting and semiconductor) model has been used which fit well with the ρ(T) data near the optimum concentration x=70%. Around this highest AFM concentration, showing maximum MR, the corresponding TEP is also higher than those of the individual parent compound, which indicates the presence of maximum grain boundary effect and defects. Positron annihilation lifetime data of the composites also support the presence of such defects and strain in the system with maximum around the critical concentration xC=70%. [ABSTRACT FROM AUTHOR]

From the low-temperature (down to 10 K) dc-magnetization data of the La0.7Sr0.3MnO3 (LSM), La0.7Ca0.3MnO3 (LCM), and Pr0.7Ca0.3MnO3 (PCM) systems, we estimated the critical exponents β, γ, and hence δ from the analysis of the modified Arrot plots. The exponent β estimated for the LCM system is less than that predicted by Heisenberg model and resides within the zone predicted by Ising model while for the LSM sample, β is higher than that predicted from the Heisenberg model which is considered to be due to the presence of dipole-dipole interaction arising from the large spin moment in the LSM system. The magnetization data of the PCM system cannot be fitted to the modified Arrot plots, which suggest highly inhomogeneous ground state even under 5 T magnetic field. Both LSM and LCM have almost equal values of γ. Seebeck coefficient data indicate a crossover from higher-temperature n-type to lower-temperature p-type conductivity behavior in both LSM and LCM systems, while the semiconducting PCM system shows p-type conductivity throughout the temperature range (300–80 K). It is noticed that for LSM system TC (Curie temperature) and TMI (metal-insulator transition temperature) are almost equal (∼360 K), whereas for the LCM system there exist a large difference between TC and TMI (TC∼245 K and TMI∼265 K), which may give some idea regarding the critical behavior of the respective samples. [ABSTRACT FROM AUTHOR]

Transport properties (resistivity and thermoelectric power) of Pb doped LaNiO3 viz. La1-xPbxNiO3-δ (0.0<=x<=0.1) show metallic behavior over a wide range of temperature (10–550 K). Pb doping (up to 10%) at the La site does not destroy the metallic behavior of LaNiO3. The paramagnetic susceptibility χ decreases with Pb doping. Above 50 K, χ is almost temperature independent and exhibits Pauli like features with a small additional Curie law contribution. The resistivity ρ increases with Pb doping though the thermoelectric power does not change proportionately, indicating that Pb doping does not introduce much disorder in the system. A linear T dependence of ρ observed above 150 K suggests the importance of electron–phonon (el–ph) interactions but at temperature below 150 K, ρ follows a T1.5 dependence. The estimated el–ph interaction constant λ increases (0.80–2.53) with Pb doping (x=0.0–0.1). No saturation of resistivity has been observed even up to 550 K with x<=0.1. The phonon frequency νph∼3444 cm-1 of the undoped sample calculated from the absorption peak of the Fourier transform infrared spectra agrees well with that at ∼3025 cm-1 estimated from the reported heat capacity data. [ABSTRACT FROM AUTHOR]

Magnetization and transport properties of La[sub 0.7]Pb[sub 0.3]MnO[sub 3]+x Ag (x=0-20 wt %) nanocomposites have been reported. In this Ag-containing colossal magnetoresistive (CMR) La[sub 0.7]Pb[sub 0.3]MnO[sub 3] composite (referred to as CMR-Ag), conductivity (σ) and metal–insulator transition temperature (T[sub p]) increase with increasing Ag. Electron microscopy and elemental mapping indicated a uniform distribution of Ag nanoparticles/clusters. The enhancement of T[sub p] is accompanied by a reduction of the c-axis lattice constant. Coexistence of interfacial tunneling with intrinsic transport behavior has been observed at the grain boundaries in the samples with a higher (>=10 wt %) Ag content. Due to the presence of nonmagnetic Ag in the ferromagnetic La[sub 0.7]Pb[sub 0.3]MnO[sub 3] material, dc magnetization decreases but the corresponding T[sub p] increases. In the low-temperature (TT[sub p]), conductivity data follow the adiabatic polaron hopping conduction mechanism. Unlike the Ag free sample, the variable-range-hopping model is found to be inapplicable for the present Ag containing nanocomposites. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pulsed magnetic field (0-4.4 T) was used to study the magnetic field dependent resistivity (12-350 K) and thermoelectric power (0-1.5 T) of Na and K-doped La[SUB0.7]Ca[SUB0.7-y]A[SUBy]MnO[SUB3] (0.0≤y≤0.3, A=Na, K) system showing semiconducting to metallic transitions around temperature T[SUBp]. Na/K-doping increases both conductivity and T[SUBp]. In La[SUB1-x]Ca[SUBx]MnO[SUB3], an increase of T[SUBp] and conductivity with an increase of Ca (for x≤0.33) are small and the small polaron coupling constant (γ) and hence the electron-lattice (phonon) interaction is strong. But in the Na/K doped system, γ is small and for y≥0.05, Motts' condition of strong el-ph interaction breaks down in the high temperature (T>T[SUBp]) phase. Increase of conductivity in the Na/K doped system is caused by the)decrease of γ, binding energy (W[SUBp]), hopping energy (W[SUBH]), and effective mass (m[SUBp]) of the polarons leading to the melting (we call it) of polarons in the T>T[SUBp] phase. This melting results in an increase)of exchange coupling constant between spins. Field dependent thermoelectric power (TEP) of the samples (measured between 80-300 K) also supports the small polaron hopping conduction. The resistivity data are well fitted with the variable range hopping model for a limited range of temperature (T[SUBp]θ[SUBD]/2. With the application of a magnetic field, the density of states at the Fermi level increases. The TEP data indicate the importance of electron-magnon contribution in the low temperature (TT[SUBp]. [ABSTRACT FROM AUTHOR]

Partial substitution of Cu by K in multicomponent glassy precursor for high T[SUBC] superconductor viz. Bi[SUB2-x]Pb[SUBx]Sr[SUB2]Ca[SUB2]Cu[SUB3]O[SUBδ](x=0.1-0.3) is found to destroy superconductivity of the corresponding annealed phase. These glasses viz. Bi[SUB2-x]Pb[SUBx]Sr[SUB2]Ca[SUB2]Cu[SUB3-y]K[SUBy]O[SUBz](x=0.1-0.3, y=0.2), however, show ferroelectric transitions (between 500 and 530 K depending on x). The corresponding K free glasses are not ferroelectric but they are good precursors for high T[SUBC] superconductor. Nanocrystalline particles/clusters (∼10-50 nm size) embedded in the K doped glasses, observed from transmission electron microscopic studies, are considered to be responsible for the ferroelectric behavior of the bulk glass nanocrystal composite (GNC). Unlike K free glasses, the K-containing glasses do not become superconductor by annealing them at higher temperature. This indicates suppression of superconductivity by the precipitation of ferroelectric nanoparticles in the K doped GNC. Though their dielectric behavior is different, both the K free and K containing glassy systems are semiconductors and follow the similar nonadiabatic small polaron hopping conduction mechanism (obeying Holstein condition). A comparative study of the properties of the two glassy systems showing distinguishing behavior has been made. [ABSTRACT FROM AUTHOR]

The effect of particle size on the transport properties (resistivity and thermopower) of La[sub 0.5]Pb[sub 0.5]MnO[sub 3] has been investigated both in the presence and in the absence of magnetic field B=0.0–1.5 T (maximum). Grain size, dc conductivity; and the metal–insulator transition temperature T[sub p] of the sample increase with increasing annealing time. Grain size has, however, comparatively little effect on the Seebeck coefficient S. Magnetoresistance is higher for the samples with smaller grain sizes. dc magnetic susceptibility also increases with increasing grain size. High temperature (T>θ[sub D]/2) resistivity data well fit the small polaron hopping model. Polaron hopping energy W[sub H] decreases but polaron radius r[sub p] increases with the increase of grain size. In the metallic regime (for TT>θ[sub D]/2), it is hard to justify this model from the temperature dependent thermopower data. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that demonstrated the use of dynamic light scattering (DLS). Measurement of the viscosity of fluids; Problems associated with DLS measurements in the diamond anvil cell; Discussion of the light scattering apparatus.

The electronic, magnetic, and thermal properties of polycrystalline Pr0.65Ca0.35-xSrxMnO3 (x=0–0.35) perovskites have been elaborately investigated. A huge enhancement of magnetoresistance (MR) (10% at H=100 Oe and 99% at H=0.5 T) has been observed in an x=0.1 sample around the metal-insulator (MI) transition temperature (TMI∼80 K) which is induced by the phase separation (PS). This study opens the possibility to search for the polycrystalline colossal magnetoresistive materials with a very high MR at low magnetic fields on the basis of PS phenomena for potential applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the magnetic response of the terbium (Tb) spins in lead strontium Tb copper oxide to the applied magnetic field by alternating current susceptibility measurements. Details of the experimental procedure; Characteristics of in-phase and out-of-phase component of susceptibility; Response of the correlated Tb to a driving magnetic field with lower frequency.

Focuses on a study which analyzed the effects of gallium doping on the magnetic ordering of praseodymium (Pr) in PrBa[sub2](Cu[sub1-x]Ga[subx])[sub3]O[sub7]. Background on the materials' magnetic and electric properties; Types of atom layers located between Pr layers; Subtraction technique used in the study.

Provides information on a study which investigated the magnetic ordering of terbium (Tb) ions in polycrystalline Pb[sub2]Sr[sub2]TbCu[sub3]O[sub8]. Magnetic properties of copper and rare earth elements; Preparation of polycrystals; Use of neutron diffraction techniques.

Structural phase transition and Néel temperature (TN) enhancement were observed in Cr-substituted Mn3O4 spinels. Structural, magnetic, and dielectric properties of (Mn1-xCrx)3O4 (where x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.40, and 0.50) were investigated. Cr-substitution induces room temperature structural phase transition from tetragonally distorted I41/amd (x = 0.00) to cubic Fd̄3m (x = 0.50). TN is found to increase from 43K (x = 0.00) to 58K (x = 0.50) with Cr-substitution. The spin ordering-induced dielectric anomaly near TN ensures that magneto-dielectric coupling persists in the cubic x = 0.50 system. X-ray absorption spectra reveal that Cr exists in a trivalent oxidation state and prefers the octahedral (Oh)-site, replacing Mn3+. Due to a reduction in the Jahn-Teller active Mn3+ cation and an increase in the smaller Cr3+ cation, the system begins to release the geometrical frustration by lowering its degeneracy. Consequently, a phase transition, from distorted tetragonal structure to the more symmetric cubic phase, occurs. [ABSTRACT FROM AUTHOR]

Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity ρ of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields. [ABSTRACT FROM AUTHOR]

We report on two-color InAs/InP(100) quantum dot lasers with tunable wavelength gap. Two peaks of lasing emission were observed simultaneously, while the high energy peak undergoes continuous blueshift with the increase in the injection current, and the low energy peak is somewhat fixed. Sophisticated studies of the wavelength gap as a function of the laser power prove that the two-peak lasing and shifting is not caused by the effect of Rabi oscillation. Moreover, comparison of electroluminescence and lasing spectra under different injection currents reveal the blueshift of the high energy peak is most likely related to the state-filling effect. [ABSTRACT FROM AUTHOR]

With increasing the Li doping level in La[SUB0.7]Ca[SUB0.3-y]Li[SUBy]MnO[SUB3] (0&les;y&les;0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La[SUP3+] and A[SUP2+] also plays an important role leading to charge localization. [ABSTRACT FROM AUTHOR]

Phonon dynamics in Bi, Bi2Se2, and CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals was investigated using femtosecond pump-probe spectroscopy. Two damped oscillations in measured transient reflectivity changes were observed, respectively, attributed to coherent optical and acoustic phonons. The frequency shift of the phonon modes in Bi-rich Bi2Se2 crystals indicates the intercalation of the additional Bi atoms into the Bi2Se3 matrix and formation of the Bi2 layer between the quintuple layers (QLs). The deformation of QLs in CuxBi2Se3 crystals was also found. These phonon dynamics results suggest that Cu atoms in CuxBi2Se3 crystals are predominantly intercalated between pair of QLs. [ABSTRACT FROM AUTHOR]

The electronic, magnetic, and thermal properties of polycrystalline Pr0.65Ca0.35-xSrxMnO3 (x=0–0.35) perovskites have been elaborately investigated. A huge enhancement of magnetoresistance (MR) (10% at H=100 Oe and 99% at H=0.5 T) has been observed in an x=0.1 sample around the metal-insulator (MI) transition temperature (TMI∼80 K) which is induced by the phase separation (PS). This study opens the possibility to search for the polycrystalline colossal magnetoresistive materials with a very high MR at low magnetic fields on the basis of PS phenomena for potential applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Structural phase transition and Néel temperature (TN) enhancement were observed in Cr-substituted Mn3O4 spinels. Structural, magnetic, and dielectric properties of (Mn1-xCrx)3O4 (where x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.40, and 0.50) were investigated. Cr-substitution induces room temperature structural phase transition from tetragonally distorted I41/amd (x = 0.00) to cubic Fd̄3m (x = 0.50). TN is found to increase from 43K (x = 0.00) to 58K (x = 0.50) with Cr-substitution. The spin ordering-induced dielectric anomaly near TN ensures that magneto-dielectric coupling persists in the cubic x = 0.50 system. X-ray absorption spectra reveal that Cr exists in a trivalent oxidation state and prefers the octahedral (Oh)-site, replacing Mn3+. Due to a reduction in the Jahn-Teller active Mn3+ cation and an increase in the smaller Cr3+ cation, the system begins to release the geometrical frustration by lowering its degeneracy. Consequently, a phase transition, from distorted tetragonal structure to the more symmetric cubic phase, occurs. [ABSTRACT FROM AUTHOR]

Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity ρ of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields. [ABSTRACT FROM AUTHOR]