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See detailDetermination of the magnetic penetration depth in a superconducting Pb film
Brisbois, Jérémy ULg; Raes, Bart; Van de Vondel, Joris et al

in Journal of Applied Physics (2014), 115(10), 103906

By means of scanning Hall probe microscopy technique we accurately map the magnetic field pattern produced by Meissner screening currents in a thin superconducting Pb stripe. The obtained field profile ... [more ▼]

By means of scanning Hall probe microscopy technique we accurately map the magnetic field pattern produced by Meissner screening currents in a thin superconducting Pb stripe. The obtained field profile allows us to quantitatively estimate the Pearl length Λ without the need of pre-calibrating the Hall sensor. This fact contrasts with the information acquired through the spatial field dependence of an individual flux quantum where the scanning height and the magnetic penetration depth combine in a single inseparable parameter. The derived London penetration depth λL coincides with the values previously reported for bulk Pb once the kinetic suppression of the order parameter is properly taken into account. [less ▲]

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See detailMagnetocaloric and transport study of poly- and nanocrystalline composite manganites La0.7Ca0.3MnO3/La0.8Sr0.2MnO3
Pekala, M; Pekala, K; Drozd, V et al

in Journal of Applied Physics (2012), 112

Magnetocaloric and transport properties are reported for novel poly- and nanocrystalline double composite manganites, La0.8Sr0.2MnO3/La0.7Ca0.3MnO3, prepared by the sol-gel method. Magnetic field ... [more ▼]

Magnetocaloric and transport properties are reported for novel poly- and nanocrystalline double composite manganites, La0.8Sr0.2MnO3/La0.7Ca0.3MnO3, prepared by the sol-gel method. Magnetic field dependence of magnetic entropy change is found to be stronger for the nano- than the polycrystalline composite. The remarkable broadening of the temperature interval, where the magnetocaloric effect occurs in poly- and nanocrystalline composites, causes the relative cooling power (RCP(S)) of the nanocrystalline composite to be reduced by only 10% compared to the Sr based polycrystalline phase. The RCP(S) of the polycrystalline composite becomes remarkably enhanced. The low temperature magnetoresistance is enhanced by 5% for the nanostructured composite. © 2012 American Institute of Physics [less ▲]

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See detailLa0.7Ca0.3MnO3 / Mn3O4 composites: does an insulating secondary phase always enhance the low field magnetoresistance of manganites?
Bhame, Shekhar ULg; Fagnard, Jean-François ULg; Pekala, Marek et al

in Journal of Applied Physics (2012), 111

Composites of magnetoresistive La0.7Ca0.3MnO3 (LCMO) with insulating Mn3O4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat ... [more ▼]

Composites of magnetoresistive La0.7Ca0.3MnO3 (LCMO) with insulating Mn3O4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat treatment. Here we report the magnetotransport properties as a function of sintering temperature Tsinter for a fixed LCMO/Mn3O4 ratio. Decreasing Tsinter from 1250°C to 800°C causes an increase in low field magnetoresistance (LFMR) that correlates with the decrease in crystallite size (CS) of the LCMO phase. When plotting LFMR at (77 K, 0.5 T) vs. 1/CS, we find that the data for the LCMO/Mn3O4 composites sintered between 800°C and 1250°C follow the same trend line as data from the literature for pure LCMO samples with crystallite size > ~25 nm. This differs from the LFMR enhancement observed by many authors in the "usual" manganite composites, i.e., composites where the insulating phase contains cations other than La, Ca or Mn. This difference suggests that diffusion of foreign cations into the grain boundary region is a necessary ingredient for the enhanced LFMR. [less ▲]

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See detailUse of second generation coated conductors for efficient shielding of DC magnetic fields
Fagnard, Jean-Francois ULg; Dirickx, Michel; Levin, G. A. et al

in Journal of Applied Physics (2010), 108

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO) coated conductors. Since effective screening of the ... [more ▼]

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO) coated conductors. Since effective screening of the axial DC magnetic field requires the unimpeded flow of an azimuthal persistent current, we demonstrate a configuration of a screening shell made out of standard YBCO coated conductor capable to accomplish that. The screen allows the persistent current to flow in the predominantly azimuthal direction at a temperature of 77 K. The persistent screen, incorporating a single layer of superconducting film, can attenuate an external magnetic field of up to 5 mT by more than an order of magnitude. For comparison purposes, another type of screen which incorporates low critical temperature quasi-persistent joints was also built. The shielding technique we describe here appears to be especially promising for the realization of large scale high-Tc superconducting screens. [less ▲]

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See detailInfluence of Adhesive Rough Surface Contact on Micro-Switches
Wu, Ling ULg; Rochus, Véronique ULg; Noels, Ludovic ULg et al

in Journal of Applied Physics (2009), 106(11), 113502

Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the ... [more ▼]

Stiction is a major failure mode in micro electro-mechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the actuation function of MEMS switches for example. Although it may be possible to avoid stiction by increasing restoring forces using high spring constants, it follows that the actuation voltage has also to be increased significantly, which reduces the efficiency. In our research, an electrostatic-structural analysis is performed to estimate the proper design range of the equivalent spring constant which is the main factor of restoring force in MEMS switches. The upper limit of equivalent spring constant is evaluated based on the initial gap width, the dielectric thickness, and the expected actuation voltage. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditions only the Van der Waals forces have to be considered for adhesion. A statistical model is used to simulate the rough surface, and the Maugis’s model is combined with Kim’s expansion to calculate adhesive forces. In the resulting model, the critical value of the spring stiffness depends on the material and surface properties, such as the elastic modulus, surface energy and surface roughness. The aim of this research is to propose simple rules for design purposes. [less ▲]

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See detailCritical field enhancement in hybrid superconductor/ferromagnet mesoscopic disks
Schildermans, N.; Silhanek, Alejandro ULg; Sautner, J. et al

in Journal of Applied Physics (2009), 105(2),

We investigated experimentally the nucleation of superconductivity in a mesoscopic hybrid structure, consisting of a thin superconducting disk covered with a ferromagnetic layer with an in-plane magnetic ... [more ▼]

We investigated experimentally the nucleation of superconductivity in a mesoscopic hybrid structure, consisting of a thin superconducting disk covered with a ferromagnetic layer with an in-plane magnetic moment. By applying a magnetic field in the plane of the structure, the remanent magnetic state of the ferromagnet can be switched from a flux-closure state where field lines are confined inside the ferromagnet to a polarized state with nonzero stray fields at the edges. This change in the magnetic state causes a drastic modification on the superconductor/normal-state phase boundary of the hybrid sample. In the polarized state a re-entrant transition line and a strong broadening of the phase boundary are observed. [less ▲]

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See detailInfluence of microstructure on the thermal conductivity of magnetoresistive La0.7Ca0.3MnO3/Mn3O4 manganite/insulating oxide polycrystalline bulk composites
Mucha, J.; Vertruyen, Bénédicte ULg; Misiorek, H. et al

in Journal of Applied Physics (2009), 105(6), 063501

We report the temperature dependence of the thermal conductivity kappa(T) of bulk polycrystalline composite samples containing a magnetoresistive manganite (La0.7Ca0.3MnO3) and an electrically insulating ... [more ▼]

We report the temperature dependence of the thermal conductivity kappa(T) of bulk polycrystalline composite samples containing a magnetoresistive manganite (La0.7Ca0.3MnO3) and an electrically insulating phase (Mn3O4). The sample porosity is shown to be a significant parameter affecting the experimental data: after porosity correction the curves display the characteristics of an ideal composite. A fit of the kappa(T) curves at low temperature using the Debye model enables the mean free path of phonons scattered on "boundaries" to be determined. The values are on the order of the grain size but are influenced by the grain arrangement and the presence of twins. [less ▲]

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See detailMagnetotransport of La0.5Ba0.5MnO3
Pekala, Marek; Drozd, V.; Fagnard, Jean-François ULg et al

in Journal of Applied Physics (2009), 105(1), 013923-013923-8

Physical properties of polycrystalline La0.5Ba0.5MnO3 are reported from low temperature (10 K) up to above room temperature. An aim has been to obtain microscopic parameters and to search for the ... [more ▼]

Physical properties of polycrystalline La0.5Ba0.5MnO3 are reported from low temperature (10 K) up to above room temperature. An aim has been to obtain microscopic parameters and to search for the characteristic lengths in terms of which one can discuss the interplay between magnetic, electric, and phonon excitations. The structural and magnetotransport measurements reveal a set of relatively high transition temperatures (near 300 K) between ferromagnetic/metallic and paramagnetic/semiconducting phases. It is found, in particular, that the so-called localization length increases from 0.085 to 0.24 nm when the magnetic field varies from 0 to 8 T. Moreover a “special field value” ~0.03 T is observed in the description of the electrical resistance. It cannot be presently distinguished whether it is the signature of a spin reorientation transition in the canted phase or a mere saturation field for aligning magnetic domains. The relatively high magnetoresistance effect (~=55% at 8 T and 10 K) makes the La0.5Ba0.5MnO3 a very interesting material for among others sensor applications. [less ▲]

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See detailA Structural, Magnetic, and Mössbauer Spectral Study of the TbCo4-xFexB Compounds with x = 0 to 2
Isnard, Olivier; Mayot, Herve; Grandjean, Fernande ULg et al

in Journal of Applied Physics (2009), 105

The TbCo4–xFexB compounds with x = 0, 1, and 2, have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron ... [more ▼]

The TbCo4–xFexB compounds with x = 0, 1, and 2, have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit cell volume and a large increase of ca. 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mössbauer spectra of the TbCo4–xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of ca. 1.7 µB, and small iron hyperfine fields of ca. 16 T. The compensation temperature of the TbCo4–xFexB compounds decreases continuously from 400 to 350 K between x = 0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects the strong hybridization of the 3d orbitals of the 6i site transition metal with the boron 2p orbitals. [less ▲]

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See detailComment on "Electronic structure and zone-center phonon modes in multiferroic bulk BiFeO3" [J. Appl. Phys. 103, 083712 (2008)]
Hermet, Patrick ULg; Goffinet, Marco ULg; Ghosez, Philippe ULg

in Journal of Applied Physics (2009), 105

In a recent paper, Tutuncu and Srivastava [J. Appl. Phys. 103, 083712 (2008)] report the electronic structure and the assignment of the zone-center phonon modes of the R3c phase of BiFeO3 using the ... [more ▼]

In a recent paper, Tutuncu and Srivastava [J. Appl. Phys. 103, 083712 (2008)] report the electronic structure and the assignment of the zone-center phonon modes of the R3c phase of BiFeO3 using the density functional theory. In the present comment, we point out some physical inaccuracies in their mode assignment. We review their interpretation and analyze which conclusions are actually justified. [less ▲]

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See detailPrinciples of design of a set-reset finite state logic nanomachine
Klein, M.; Levine, R. D.; Remacle, Françoise ULg

in Journal of Applied Physics (2008), 104(4),

Pulsed electrical set and reset inputs are used to simulate the temporal action of a finite state machine in a three terminal configuration for a variety of arrangements. The gate electrode is necessary ... [more ▼]

Pulsed electrical set and reset inputs are used to simulate the temporal action of a finite state machine in a three terminal configuration for a variety of arrangements. The gate electrode is necessary only if it is of interest to tune the tunneling rate and to compensate for background charges. When the output is the current, a source and drain electrodes are required. If the output is determined by measuring charge occupancy, then a single junction suffices. The electron transfer rates are computed from the free energy change for a single electron transfer to or from a quantum dot of size such that only charge quantization matters. For a small enough dot the device could operate at room temperature. An asymmetric configuration of the source and drain favors a longer term time preservation of the memory of the device. An alternative design that operates with the same energetics and kinetic parameters is to pulse the resistance rather than the voltage. (C) 2008 American Institute of Physics. [less ▲]

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See detailInfluence of Zeeman splitting and thermally excited polaron states on magnetoelectrical and magnetothermal properties of magnetoresistive polycrystalline manganite La0.8Sr0.2MnO3
Sergeenkov, S.; Mucha, Jan ULg; Pekala, M. et al

in Journal of Applied Physics (2007), 102(8),

Some possible connection between spin and charge degrees of freedom in magnetoresistive manganites is investigated through a thorough experimental study of the magnetic [alternating current susceptibility ... [more ▼]

Some possible connection between spin and charge degrees of freedom in magnetoresistive manganites is investigated through a thorough experimental study of the magnetic [alternating current susceptibility and direct current (dc) magnetization) and transport (resistivity and thermal conductivity) properties. Measurements are reported in the case of well characterized polycrystalline La0.8Sr0.2MnO3 samples. The experimental results suggest rather strong field-induced polarization effects in our material, clearly indicating the presence of ordered ferromagnetic regions inside the semiconducting phase. Using an analytical expression which fits the spontaneous dc magnetization, the temperature and magnetic field dependences of both electrical resistivity and thermal conductivity data are found to be well reproduced through a universal scenario based on two mechanisms: (i) a magnetization dependent spin polaron hopping influenced by a Zeeman splitting effect and (ii) properly defined thermally excited polaron states which have to be taken into account in order to correctly describe the behavior of the less conducting region. Using the experimentally found values of the magnetic and electron localization temperatures, we obtain L=0.5 nm and m(p) = 3.2 me for estimates of the localization length (size of the spin polaron) and effective polaron mass, respectively. (C) 2007 American Institute of Physics. [less ▲]

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See detailMagnetocaloric effect and magnetic properties of Tb0.9Sn0.1MnO3
Fabris, Frederik Wolff; Pekala, Marek; Drozd, V. et al

in Journal of Applied Physics (2007), 101(10), 103904

The magnetocaloric effect in magnetic materials is of great interest nowadays. In this article we present an investigation about the magnetic properties near the magnetic transition in a polycrystalline ... [more ▼]

The magnetocaloric effect in magnetic materials is of great interest nowadays. In this article we present an investigation about the magnetic properties near the magnetic transition in a polycrystalline sample of a manganite Tb0.9Sn0.1MnO3. Particularly, we are interested in describing the nature of the magnetic interactions and the magnetocaloric effect in this compound. The temperature dependence of the magnetization was measured to determine the characteristics of the magnetic transition and the magnetic entropy change was calculated from magnetization curves at different temperatures. The magnetic solid is paramagnetic at high temperatures. We observe a dominant antiferromagnetic interaction below T-n=38 K for low applied magnetic fields; the presence of Sn doping in this compound decreases the Neel temperature of the pure TbMnO3 system. A drastic increase in the magnetization as a function of temperature near the magnetic transition suggests a strong magnetocaloric effect. We found a large magnetic entropy change Delta S-M(T) of about -4 J/kg K at µ0H=3 T. We believe that the magnetic entropy change is associated with the magnetic transition and we interpret it as due to the coupling between the magnetic field and the spin ordering. This relatively large value and broad temperature interval (about 35 K) of the magnetocaloric effect make the present compound a promising candidate for magnetic refrigerators at low temperatures. (c) 2007 American Institute of Physics. [less ▲]

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See detailA Mossbauer spectral study of the GdCo4-xFexB compounds
Grandjean, Fernande ULg; Hermann, Raphaël ULg; Popiel, E. et al

in Journal of Applied Physics (2007), 101(2),

The iron-57 Mossbauer spectra of the GdCo4-xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small iron hyperfine fields ... [more ▼]

The iron-57 Mossbauer spectra of the GdCo4-xFexB compounds, where x is 0.10, 0.15, 0.20, 0.25, 1, 2, 2.5, and 2.6, have been measured at room temperature and reveal relatively small iron hyperfine fields of approximately 12-18 T, relatively large quadrupole interactions of approximately +0.9 and -1 mm/s, and three very different types of spectra for x=0.10 and 0.15, x=0.25, 1, and 2, and x=2.5 and 2.6. The differences result from both the different easy magnetization directions in these compounds and the different cobalt and/or iron occupancies of the crystallographic 2c and 6i sites. The spectra have been fitted by calculating the spectral absorption with the complete iron-57 nuclear excited state Hamiltonian for the iron 2c and 6i sites. The fits have used an asymmetry parameter eta and Euler angles theta and phi that relate the hyperfine field to the iron electric field gradient axes of each crystallographic site in an orientation that is consistent with the structural and magnetic properties of the site. The results of the fits indicate both that the full Hamiltonian approach is required for physically reasonable spectral fits and that the small observed fields result from the presence of large orbital contributions which subtract from the Fermi contact contributions to the magnetic hyperfine fields of the two sites. The iron 2c occupancy obtained from the Mossbauer spectral area has been used to model the compositional dependence of the magnetic anisotropy constant in the GdCo4-xFexB compounds. (c) 2007 American Institute of Physics. [less ▲]

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See detailDoes the orbital degeneracy play any role in the high thermopower of lamellar cobaltites?
Pollet, M.; Doumerc, J. P.; Guilmeau, E. et al

in Journal of Applied Physics (2007), 101(8),

This article investigates the role of the CoO6 octahedron distortion on the electronic properties and more particularly on the high value of the Seebeck coefficient in the BiCaCoO lamellar cobaltites. Our ... [more ▼]

This article investigates the role of the CoO6 octahedron distortion on the electronic properties and more particularly on the high value of the Seebeck coefficient in the BiCaCoO lamellar cobaltites. Our measurements provide clues indicating that the t2g orbital degeneracy lifting has to be considered to account for the observed high temperature limit of the thermopower. They also provide experimental arguments for locating the a1g and eg′ orbitals levels on the energy scale, through the compression of the octahedron. These results are in agreement with recent ab initio calculation including the electronic correlations and concluding for the inversion of these levels as compared to the expectation from the crystal field theory. © 2007 American Institute of Physics. [less ▲]

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See detailScaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures
Nagarajan, V.; Junquera, J.; He, J. Q. et al

in Journal of Applied Physics (2006), 100

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution ... [more ▼]

Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c/a similar to 1.058) is maintained down to 50 angstrom thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (Delta P) using a pulsed probe setup and the out-of-plane piezoelectric response (d(33)) revealed a systematic drop from similar to 140 mu C/cm(2) and 60 pm/V for a 150 angstrom thick film to 11 mu C/cm(2) and 7 pm/V for a 50 angstrom thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180 degrees polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity. (c) 2006 American Institute of Physics. [less ▲]

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See detailNonlinear compressibility effects in fluid-structure interaction and their implications on the air-blast loading of structures
Kambouchev, Nayden; Noels, Ludovic ULg; Radovitzky, Raúl

in Journal of Applied Physics (2006), 100(6), 063519

The impulse imparted by a blast wave to a freestanding solid plate is studied analytically and numerically focusing on the case in which nonlinear compressibility effects in the fluid are important, as is ... [more ▼]

The impulse imparted by a blast wave to a freestanding solid plate is studied analytically and numerically focusing on the case in which nonlinear compressibility effects in the fluid are important, as is the case for explosions in air. The analysis furnishes, in effect, an extension of Taylor's pioneering contribution to the understanding of the influence of fluid-structure interaction (FSI) on the blast loading of structures [The Scientific Papers of Sir Geoffrey Ingram Taylor, edited by G. K. Batchelor (Cambridge University Press, Cambridge, 1963), Vol. III, pp. 287-303] to the nonlinear range. The limiting cases of extremely heavy and extremely light plates are explored analytically for arbitrary blast intensity, from where it is concluded that a modified nondimensional parameter representing the mass of compressed fluid relative to the mass of the plate governs the FSI. The intermediate asymptotic FSI regime is studied using a numerical method based on a Lagrangian formulation of the Euler equations of compressible flow and conventional shock-capturing techniques. Based on the analytical and numerical results, an approximate formula describing the entire range of relevant FSI conditions is proposed. The main conclusion of this work is that nonlinear fluid compressibility further enhances the beneficial effects of FSI in reducing the impulse transmitted to the structure. More specifically, it is found that transmitted impulse reductions due to FSI when compared to those obtained ignoring FSI effects are more significant than in the acoustic limit. This result can be advantageously exploited in the design and optimization of structures with increased blast resistance. (c) 2006 American Institute of Physics. [less ▲]

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See detailSpin-cluster effect and lattice-deformation-induced Kondo effect, spinglass freezing, and strong phonon scattering in La0.7Ca0.3Mn1-xCrxO3
Wu, Bai-Mei; Li, Bo; Zhen, Wei-Hua et al

in Journal of Applied Physics (2005), 97(10, Part 1), 103908

Besides the Kondo effect observed in dilute magnetic alloys, the Cr-doped perovskite manganate compounds La0.7Ca0.3Mn1-xCrxO3 also exhibit Kondo effect and spin-glass freezing in a certain composition ... [more ▼]

Besides the Kondo effect observed in dilute magnetic alloys, the Cr-doped perovskite manganate compounds La0.7Ca0.3Mn1-xCrxO3 also exhibit Kondo effect and spin-glass freezing in a certain composition range. An extensive investigation for the La0.7Ca0.3Mn1-xCrO3 (x=0.01, 0.05, 0.10, 0.3, 0.6, and 1.0) system on the magnetization and ac susceptibility, the resistivity and magnetoresistance, as well as the thermal conductivity is done at low temperature. The spin-glass behavior has been confirmed for these compounds with x=0.05, 0.1, and 0.3. For temperatures above T-f (the spin-glass freezing temperature) a Curie-Weiss law is obeyed. The paramagnetic Curie temperature 0 is dependent on Cr doping. Below T-f there exists a Kondo minimum in the resistivity. Colossal magnetoresistance has been observed in this system with Cr concentration up to x=0.6. We suppose that the substitution of Mn with Cr dilutes Mn ions and changes the long-range ferromagnetic order of La0.7Ca0.3MnO3. These behaviors demonstrate that short-range ferromagnetic correlation and fluctuation exist among Mn spins far above T-f. Furthermore, these interactions are a precursor of the cooperative freezing at T-f. The "double bumps" feature in the resistivity-temperature curve is observed in compounds with x= 0.05 and 0.1. The phonon scattering is enhanced at low temperatures, where the second peak of double bumps comes out. The results indicate that the spin-cluster effect and lattice deformation induce Kondo effect, spin-glass freezing, and strong phonon scattering in mixed perovskite La0.7Ca0.3Mn1-xCrO3. (c) 2005 American Institute of Physics. [less ▲]

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See detailBlueshifted Raman scattering and its correlation with the [110] growth direction in gallium oxide nanowires
RAO, Rita Flora ULg; Rao, A. M.; Xu, Bin ULg et al

in Journal Of Applied Physics (2005), 98(9),

The Raman spectrum of gallium oxide (beta-Ga2O3) nanowires with [001] growth direction is identical to that of the bulk Ga2O3 [Y. C. Choi Adv. Mater. 12, 746 (2000)] while that of beta-Ga2O3 nanowires ... [more ▼]

The Raman spectrum of gallium oxide (beta-Ga2O3) nanowires with [001] growth direction is identical to that of the bulk Ga2O3 [Y. C. Choi Adv. Mater. 12, 746 (2000)] while that of beta-Ga2O3 nanowires with [40 (1) over bar] growth direction is redshifted by 4-23 cm(-1) [Y. H. Gao Appl. Phys. Lett. 81, 2267 (2002)]. Here we report the Raman and Fourier transform infrared spectra of beta-Ga2O3 nanowires with [110] growth direction which is blueshifted relative to the bulk spectra by similar to 10-40 cm(-1). Based on a first principles calculation of the strain dependence of Raman mode frequencies in bulk beta-Ga2O3, we correlate the observed frequency shifts to growth-direction-induced internal strains in the nanowires. (c) 2005 American Institute of Physics. [less ▲]

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See detailUnusual thermoelectric behavior of packed crystalline granular metals
Ausloos, Marcel ULg; Pekala, Marek; Latuch, J. et al

in Journal of Applied Physics (2004), 96(12), 7338-7345

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted ... [more ▼]

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature (T) from 15 to 300 K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235 K, (ii) with various dependencies, e.g., similar ~ T(-3/4) at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60 K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes-for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy. (C) 2004 American Institute of Physics. [less ▲]

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