Search

In this paper, we study the effect of the signal-to-noise ratio of magnetization measurements on the determination of the Curie temperature from the analysis of the magnetocaloric response. The procedure has been compared with the method of the inflection point of the magnetization versus temperature curves. Magnetization data have been simulated using the Arrott–Noakes equation of state, with the addition of different noise levels (either 1% of the measured signal or 0.3% of the measurement range). It is shown that the obtained values of the Curie temperature are more accurate in the case of the magnetocaloric procedure, although this method requires more data analysis than the inflection point method. Moreover, the field independence of the Curie temperature obtained from the magnetocaloric procedure allows us to perform a statistical analysis of the obtained values, reducing the associated error in the Curie temperature determination.

Iron oxide-based nanoparticles have been modified in their core with holmium(III) in an amount affecting only slightly their magnetic properties. Nanoparticles were conjugated covalently with biomolecule of trastuzumab (Herceptin&reg, ), the monoclonal antibody that recognizes cancer cells overexpressing HER2 receptors targeting such nanoparticles to the specified tumor tissues. Systematic studies of Ho3+-doped bioconjugates were carried out as a preliminary step for future replacement of &lsquo, cold&rsquo, Ho with 166Ho radionuclide, emitting &lsquo, soft&rsquo, beta(-) radiation for possible targeted radionuclide therapy. Physicochemical properties of the obtained bioconjugates were subsequently tested for use in magnetic hyperthermia, considered as an effective, low-invasiveness anticancer therapy. With such a system we expect to achieve both: active targeting and multimodal action by simultaneous internal and localized irradiation and magnetic hyperthermia of specific cancers.

The Griffiths like phase embedded into paramagnetic matrix of mixed valence orthorhombic nanocrystalline manganite La0.50Ca0.50MnO3 is experimentally studied by means of sensitive magnetic susceptibility and electron spin resonance. A comparative study of the nano- and polycrystalline manganites indicates the temperature interval of the Griffiths like phase located above the Curie temperature of nanocrystalline one. The upper temperature limit for an existence of Griffiths like phase, revealed by the sensitive electron spin resonance, is 10 K higher than that of the magnetic susceptibility. This proves that the high frequency field is able to excite the relatively smaller magnetic clusters.

Poly- and nanocrystalline manganite composites (1/3)La0.7Ca0.3MnO3/(2/3)La0.8Sr0.2MnO3 prepared by the sol–gel method are studied by magnetic and transport measurements. The Arrott plots and universal curve of magnetic entropy change confirm that magnetic transition is of the second order. The magnetocaloric effect of polycrystalline composite is found to be roughly twice smaller as compared to the polycrystalline Ca- and Sr-based parent phases. The nanocrystalline composite of the same composition exhibits only 8% reduction of magnetic entropy change. Due to the large temperature spread of magnetocaloric effect the relative cooling power RCP of nanocrystalline composite is about three times larger as compared to the nanocrystalline Ca- and Sr-based parent phases. The maximum magnetic entropy change DSMAX and relative cooling power RCP are found to be more sensitive to magnetic field strength for the nano- than for polycrystalline composites studied.

Pr 0.55 K 0.05 Sr 0.4 MnO 3 sample have been synthesized using the conventional solid state reaction. Rietveld refinements of the X-ray diffraction patterns at room temperature confirm that the sample is single phase and crystallizes in the orthorhombic structure with P nma space group; the crystallite size is around 70 nm. The SEM images show that grain size spreads around 1000–1200 nm. DTA analysis does not reveal any clear transition in temperature range studied. The low-temperature DSC indicates that Curie temperature is around 297 K. Magnetization measurements in a magnetic applied field of 0.01 T exhibit a paramagnetic–ferromagnetic transition at the Curie temperature T C = 303 K. A magnetic entropy change under an applied magnetic field of 2 T is found to be 2.26 J kg − 1 K −1 , resulting in a large relative cooling power around 70 J/kg. Electrical resistivity measurements reveal a transition from semiconductor to metallic phase. The thermal conductivity is found to be higher than that reported for undoped and Na doped manganites reported by Thaljaoui et al. (2013).

The monovalent potassium doped manganites Pr 0.6 Sr 0.4− x K x MnO 3 ( x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature.

The manganite Pr0.55Na0.05Sr0.4MnO3 prepared by solid state reaction has the orthorhombic structure and mean crystallite size of 51 nm. Scanning electron microscopy (SEM) shows that the grains are irregularly spherical like shaped with sizes 400 to 700 nm. In vicinity of Curie temperature equal to 289 K the magnetic entropy change |ΔSMmax| attains 1.75 J kg−1 K−1 under an applied magnetic field of 2 T which corresponds to relative cooling power of 93 J/kg. Electrical resistivity measurements reveal a transition from metallic to semiconductor phase. Temperature variation of electrical resistivity was fitted by the small polaron hopping (SPH) and Mott’s Variable range Hopping (VRH) models. The activation energy and Mott temperature are found to decrease and N(EF) to increase in magnetic field varying from zero to 1 T. The phonon contribution dominates in thermal conductivity.

A systematic investigation of structural, magnetic, and magnetocaloric properties is reported for a series of monovalent sodium-doped manganites Pr0.6Sr0.4−x Na x MnO3 (x = 0, 0.05, 0.1, 0.15, and 0.2). Rietveld refinements of the X-ray diffraction patterns show that all powder samples are single-phased and crystallized in the orthorhombic structure with Pnma space group. Magnetic characterization and Arrott plot confirm the second-order phase transition at Curie temperature T C decreasing from 310 K for x = 0 down to 272 K for x = 0.2. Magnetic entropy change is largest for x = 0 reaching 1.95 J kg−1 K−1 at 2 T field. This corresponds to a large relative cooling power of 102 J kg−1 . Magnetic field sensitivity of magnetic entropy change and relative cooling power are analyzed and discussed.

The electrical resistivity in the mixed state of Bi2212 tape superconductors can be accurately reconstructed for values below approximately a half of the normal state value of resistivity, assuming a Gaussian distribution for the vortex lattice melting temperatures. The magnetic field dependences of the distribution width and of the dBc2/dT parameter were calculated. Moreover the vortex liquid viscosity coefficient was determined between the vortex lattice melting temperature and Tc at various magnetic fields. It is pointed out that the vortex lattice melting transition should not be confused with the irreversibility line of magnetic studies nor with the percolation temperature line for electrical resistivity. © 1998 Elsevier Science B.V. All rights reserved.

The orthorhombic Sr-doped manganite Pr 0.6 Sr 0.35 Na 0.05 MnO 3 synthesized using the conventional solid state reaction at high temperature is characterized by magnetic and electron transport studies. Structural data shows that crystallite size (32 nm) is found to be 15 times smaller than the mean grain size (500 nm). Magnetic measurements reveal the strong magnetocaloric effect in vicinity of the Curie temperature T C = 300 K. The considerable magnetic entropy change |ΔSM max | = 1.84 J/(kg K) found for an applied magnetic field of 2 T results in large relative cooling power RCP with a maximum value of 92 J/kg. Peculiar temperature variation of electrical resistivity and negative magnetoresistance are discussed and related to grain sizes and grain boundaries.

Effect of monovalent Na doping on the magnetic properties is studied in Pr0.6Sr0.4−xNaxMnO3 system (x = 0, 0.05) using X-band electron magnetic resonance and magnetization measurements. Temperature variation of magnetic resonance spectra of doped and undoped manganites is analyzed for paramagnetic and ferromagnetic states and compared to similar systems. In paramagnetic phase the magnetic susceptibility proportional to resonance signal intensity is found to obey the Curie–Weiss law. The effective magnetic moment becomes smaller in doped manganite. The paramagnetic Curie temperature derived from signal intensity equals to 312 and 306 K for the undoped and doped manganites, respectively, and is close to values obtained from magnetization variation in paramagnetic phase. The activation energy determined using the adiabatic small polaron hopping model is higher for the undoped than the doped manganite, which proves that the Na doping slightly reduces the Mn3+/Mn4+ double exchange interactions.

Crystals of PrxLa1−xAlO3 solid solution have been grown by the Czochralski method for the first time, to the best of our knowledge. Crystals with high praseodymium concentration tend to grow spirally. The color of the crystals changes with chemical composition. X-ray diffraction shows an increase of the lattice constants with an increase in lanthanum ion concentration. The thermal conductivity has been investigated in the temperature range from 5 to 300 K. Completely different behavior of thermal conductivity is observed at low temperatures for the investigated crystals, whereas it remains roughly constant at high temperatures. The values of magnetic susceptibility lie within the expected range that could be expected for a paramagnetic material.

Structure, magnetic and magnetocaloric properties of poly- and nanocrystalline La0.5Ca0.5MnO3 manganites prepared by the citrate sol–gel method are studied in a broad temperature range. The Arrott plots show that the phase transition is of the second order. The cooling efficiency of 93–97 J/kg is found for the poly- and nanocrystalline samples. The relatively weaker magnetocaloric effect in nanocrystalline La0.5Ca0.5MnO3 is spread over temperature range almost three times broader than for the polycrystalline one. Charge ordering effects decay in manganites with grain sizes below 150 nm.

Magnetic and structural investigation of Fe 80 Zn 20 systems shows that various methods of mechanosynthesis result in fine structures with crystallite sizes between 20 and 100 nm. All the systems studied exhibit strong magnetic ordering with Curie temperatures between 870 and 1000 K. The coercive fields and magnetic energy losses are compared for various milling conditions.

Results of X-ray absorption fine structure measurements in manganites (La 1-x Ho x ) 2/3 Ca 1/3 MnO 3 with 0.15 < x < 0.50 are presented. When LaMnO 3 is doped with a, divalent element such as Ca 2+ , substituting for La 3+ , holes are induced in the filled Mn d orbitais. This leads to a, strong ferromagnetic coupling between Mn sites. Ca ions in La 1-x Ca x MnO 3 introduce a distortion of the crystal lattice and mixed valence Mn ions (Mn 3+ and Mn 4+ ). On the other hand, in manganites (La 1-x Ho x ) 2/3 Ca 1/3 MnO 3 the substitution of La for Ho causes a lattice distortion and induces a disorder, which reduces a magnetic interaction. The ferromagnetic transition temperature and conductivity decrease very quickly with increasing x. The magnetic and transport properties of compounds depend on the local atomic structure around Mn ions. The information on the bond lengths and Debye-Waller factor are obtained from the extended X-ray absorption fine structure (EXAFS) data analysis. The charge state of Mn is determined from the position of the absorption edge in X-ray absorption near edge structure (XANES) data. XAFS results are in good agreement with magnetic characteristics of the studied materials.

Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.

The structural, magnetic and electrical transport properties of the Sn-doped TbMnO3 manganites are studied by X-ray diffraction, ac susceptibility, dc magnetization and electrical resistivity measurements. The Sn doping into the Tb and Mn sites of TbMnO3 compresses the unit cell and changes parameters of the antiferromagnetic phase whereas the magnetic moment of Mn are only weakly affected. The electrical resistivity of doped manganites is reduced and the activation energy EA is determined for the thermally activated conduction.

Polycrystalline solid solutions Sr1−xKxPbO3−yFy (0 ≤ x, y ≤ 0.20) were synthesized. Their structural properties were determined by X-ray diffraction. Resistivity and thermoelectric power were measured as functions of temperature. It was shown that a simultaneous substitution of potassium for strontium and fluorine for oxygen results in a transformation of conductivity from semiconductive to metallic at low temperatures. The results are discussed in connection with possible superconductivity in new families of doped perovskites.

Differential conductance G as a function of the bias voltage V was measured for break-junctions of superconducting Bi2Sr2CaCu2O8+δ and YBa2Cu3O7−δ. The dependences G(V ) for both materials clearly demonstrate the so-called dip–hump structures outside the gap region. A theory, which suggests the charge-density-wave origin of the dip–hump structures and explains its specific form by intrinsic inhomogeneity of cuprate materials, was developed. The well-known pseudogap features in the tunnel spectra of high-Tc oxides found both below and above the superconducting critical temperature are also described by the theory, which testifies that both the pseudogap and the dip–hump structures have the same origin. Competing theories and various G(V ) peculiarities found for a number of superconducting oxides are briefly discussed.

Polycrystalline samples of the La 0.8 Sr 0.2 MnO 3 manganite were prepared by the carbonate precursor method and structurally characterized by X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect is determined and compared to the similar systems. The magnetocaloric effect in polycrystalline manganite is shifted less than 20 K below that one of the single crystal. The relative cooling power being more than one third of RCP(S) for the magnetocaloric standard of metallic Gd suggests a possible application for magnetic cooling around the room temperature.

The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, electrical resistivity and thermoelectric measurements. The isovalent Gd substitution causes that the metal–insulator transition is removed, whereas the negative magnetoresistance effect is weak. The electrical resistivity is described by the small polaron model.

The aim of this work was to obtain bulk nanocrystalline austenitic steel by ball milling of steel powders and their compaction. For powder compaction pulse plasma sintering method was used. Ball milling of 316L austenitic steel powders in a planetary Fritsch P5 mill resulted in the two-phase structure consisting of austenite and martensite. Both phases exhibited crystallite size in the range 10–20 nm. The maximum content of martensite reached 66% and was observed after short processing time. The decrease of its contribution was observed after prolonged milling and was explained by stabilization of nanocrystalline austenite and residual stresses. Pulse current sintering technique allowed obtaining fully dense samples exhibiting austenitic structure characterized by grain size in the range 150–300 nm and microhardness 400 HV 0.3 .

High-energy ball milling technique with subsequent heat treatment were used to prepare the nanocrystalline Fe 41 Ni 20 Co 20 Zr 7 B 12 alloy. The powder samples were obtained by mechanical milling of the melt-spun amorphous ribbon and by mechanical alloying of the mixture of pure elemental powders with the corresponding composition. Combined X-ray diffraction and Mossbauer spectroscopy measurements allowed the structural characterization of the samples. The powder prepared from the ribbon remained amorphous after milling for 27 h, while the milling of the mixture of crystalline elements for 200 h led to the formation of the nanocrystalline iron-based random solid solution. Differential scanning calorimetry results revealed three exothermic peaks, however, crystallization temperatures determined for the nanocrystalline powder were much lower that those obtained for the amorphous one. The first two stages correspond to the formation of the bcc FeCo nanograins. Annealing at higher temperatures caused the crystallization of the bcc phase followed by the formation of the iron-based borides. The magnetization measurements performed as a function of temperature confirmed the amorphous and crystalline states of the ball milled ribbon and mechanically alloyed elemental powders, respectively. The Curie temperature of the amorphous ribbon is markedly higher than that of the amorphous powder.

Samples of La0.7Ca0.3Mn1-xGaxO3 with x = 0, 0.025, 0.05 and 0.10 were prepared by standard solid-state reaction. They were first characterized chemically, including the microstructure. The magnetic properties and various transport properties, i.e. the electrical resistivity, magnetoresistivity (for a field below 8T), thermoelectric power and thermal conductivity measured each time on the same sample, are reported. The markedly different behavior of the x = 0.1 sample from those with a smaller Ga content, is discussed. The dilution of the Mn3+/Mn4+ interactions with Ga doping considerably reduces the ferromagnetic double exchange interaction within the manganese lattice leading to a decrease of the Curie temperature. The polaron binding energy varies from 224 to 243 meV with increased Ga doping., Comment: submitted to J Magnet Magnet Mater; 13 figures; 2 tables; 38 references

The voltage, V , dependences of the differential tunnel conductance G(V ) were calculated for two kinds of junctions involving normal and superconducting charge-density-wave metals (CDWMs) in the external magnetic field H. The first is a non-symmetrical junction with a CDWM electrode being biased with respect to a ferromagnet. Calculations show that the paramagnetic splitting occurs between spin-up and spin-down components of G(V ), similar to what is observed when a superconducting electrode is used instead of the CDWM one. The second setup is symmetric (CDWM– I–CDWM), where I denotes an insulator. If at least one of the CDWM electrodes is normal and H 6= 0, G(V ) will also be spin-split.

The following report considers textured materials of the DyBa2Cu3O7 type seeded with a Nd123 seed as initiator. They are grown with an excess 20% Dy211 phase on a Dy2O3 substrate. We report chemical characterizations, electrical resistivity, thermoelectric power and thermal conductivity over a broad temperature range as a function of an applied magnetic field up to 6 T. We show that specific features appear on the magneto thermal transport properties different in these materials from those found in single crystals and polycrystalline samples. We propose that two vortex regimes can be distinguished in the mixed phase, - due to the intrinsic microstructure. We calculate the viscosity, entropy and figure of merit of the samples., Comment: 18 pages, with 8 figures; 4 color figuresx missing (much memory needed)

X-ray diffraction, Mossbauer spectroscopy and magnetization measurements were used to study the structure and some magnetic properties of Fe 50 Ge 50 and Fe 62 Ge 38 prepared by mechanical alloying from the elemental powders. In both cases in the early stages of milling the intermediate paramagnetic FeGe 2 phase was formed. The mechanical alloying process of Fe 50 Ge 50 resulted in the formation of the paramagnetic FeGe (B20) phase with an average crystallite size of about 15 nm. In the case of the Fe 62 Ge 38 , the ferromagnetic Fe 5 Ge 3 (β) phase with a Curie temperature of about 430 K was obtained. The average crystallite size was about 9 nm. The average hyperfine magnetic field of about 16 T allowed it to determine that more than four germanium atoms exist in the nearest environment of the 57 Fe isotopes in the Fe 5 Ge 3 phase.

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 300K. 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 dependences, e.g. $\simeq$ $T^{-3/4}$ at low $T$, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60K, 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., to be published in J. Appl. Phys.22 pages, 8 figures

Solid solutions Sr 1-x La x PbO 3-δ with x = 0, 0.05, 0.1. 0.15, 0.2 and 0.25 were synthesized by oxalate precursor coprecipitation methods. The solid solutions obtained were analyzed by the XRD technique and iodometric titration. Resistivity p and thermoelectric power S were measured for temperatures 20 K < T < 300 K. The parent compound SrPbO 3-δ shows a shallow minimum of p(T) at about 120 K, whereas p(T) for the La-doped samples are rather smooth with weakly manifested inflection points for all investigated compositions. The thermoelectric power is negative. The transport data demonstrate that the ceramic samples Sr 1-x La x PbO 3-δ are unstable towards electron spectrum dielectrization or localization of current carriers. From the analysis of the measured properties it may be inferred that the effects of disorder and granularity and the inter-grain tunneling, in particular, strongly influence transport phenomena.

Precise magnetotransport studies of heat and charge carriers in polycrystalline MgB2 show that magnetic fields up to 8 T remarkably influence electrical resistivity, thermoelectric power and thermal conductivity. The superconducting transition temperature shifts from 39 K to 19 K at 8 T as observed on electric signals. The temperature transition width is weakly broadened. Electron and phonon contributions to the thermal conductivity are separated and discussed. The Debye temperature calculated from a phonon drag thermoelectric power component is inconsistent with values derived through other effects.

New ceramics of Sr 1− x K x PbO 3− δ with x =0, 0.05, 0.1, 0.15 and 0.2 were synthesized and analyzed. Temperature, T , variations of resistivity, ρ , and thermoelectric power, S , were measured for 20 T T , the thermal resistivity coefficients d ρ /d T for all compositions were found to be negative, which suggests localization of current carriers or the appearance of a dielectric gap in the electron structure. The analysis of the ρ ( T ) curve shows that the electrical conduction has at least a substantial contribution from the tunneling processes at the grain boundaries. The thermoelectric power S is negative for all compositions and for all T , thus indicating electron-like conduction. The collection of data demonstrates that the parent substance SrPbO 3 is on the verge of the metal–insulator transition and different kinds of doping may substantially change the transport properties and the degree of current carrier degeneracy. The system seems to be promising as a building block for new superconducting families.

Structural and magnetic properties of bulk amorphous alloys Fe 74 Al 4 Ga 2 P 12 B 4 Si 4 (A), Fe 76 Al 4 P 12 B 4 Si 4 (B), Fe 80 P 12 B 4 Si 4 (C) and Fe 74 Al 4 Ga 2 P 8 B 4 Si 8 (D) fabricated by a single-roller melt-spinning method were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), magnetic measurements and Mossbauer spectroscopy (MS). The supercooled liquid region up to 45 K was determined from the DSC spectra. Magnetic and MS measurements revealed strong ferromagnetic ordering in the ribbons. XRD and MS were used to recognise the phases formed during annealing of the alloys. The average magnetisation became more random after annealing of samples A and B, while for the ribbons C and D an in-plane orientation of magnetisation was found.

$La_{0.7}Ca_{0.3}MnO_3$ samples were prepared in nano- and polycrystalline forms by sol-gel and solid state reaction methods, respectively, and structurally characterized by synchrotron X-ray diffraction. The magnetic properties determined by ac susceptibility and dc magnetization measurements are discussed. The magnetocaloric effect in this nanocrystalline manganite is spread over a broader temperature interval than in the polycrystalline case. The relative cooling power of the poly- and nanocrystalline manganites is used to evaluate a possible application for magnetic cooling below room temperature., 6 pages, 5 (double) figures, 1 table, 16 references; submitted to Appl. Phys. A

Current–voltage characteristics for junctions involving normal and superconducting charge-density-wave metals in the magnetic field were calculated. Spin splitting was found both for symmetrical and non-symmetrical junctions.

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.

Tunnel conductances G(V) = dJ/dV(V), where J(V) is the quasiparticle current and V is the voltage, have been calculated for nonsymmetric (CDWS-I-N) and symmetric (CDWS-I-CDWS) tunnel junctions (N, I, and CDWS stand for a normal metal, insulator, and electronically inhomogeneous CDW superconductor, respectively). The CDWS inhomogeneity was shown to be responsible for the appearance of smooth but conspicuous dip-hump structures (DHSs) in G(V) at T » Tc. At higher T, the DHS transforms into a broad pseudogap depletion in the density of states. Good qualitative agreement was obtained between theoretically calculated and experimental G(V) dependences.

Physical properties of polycrystalline La 0.5 Ba 0.5 MnO 3 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. © 2009 American Institute of Physics. DOI: 10.1063/1.3032326

Some possible connection between spin and charge degrees of freedom in magneto-resistive manganites is investigated through a thorough experimental study of the magnetic (AC susceptibility and DC magnetization) and transport (resistivity and thermal conductivity) properties. Measurements are reported in the case of well characterized polycrystalline La_{0.8}Sr_{0.2}MnO_3 samples. The experimental results suggest rather strong field-induced polarization effects in our material, clearly indicating the presence of ordered FM 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=0.5nm and m_p=3.2m_e for estimates of the localization length (size of the spin polaron) and effective polaron mass, respectively., Comment: Accepted for publication in Journal of Applied Physics

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 Tn=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 en...

Thermoelectric power study of magnetic amorphous alloys Fe x Ni 80-x B y Si 20-y is reported. The sensitivity of TEP to the ferro - paramagnetic transition as well as to the crystallization effects is indicated. It is concluded that the Grest - Nagel model gives more appropriate description of electron transport in magnetic amorphous alloys than the Ziman theory. The TEP behaviour in crystallized alloys is discussed using the Kasuya theory.

Thermomagnetic and thermoelectric studies were performed on 1) ferromagnetic metallic glasses of the Fe-Ni-B-Si system and 2) ferro- and paramagnetic ones containing the rare earth elements. The characteristic nonlinear temperature variation of thermoelectric power found for all ferromagnetic alloys supports the applicability of the Grest - Nagel model to the electron transport phenomena in magnetically ordered amorphous solids. This model is additionally confirmed by information on the hyperfine field distribution obtained from Mossbauer spectroscopy. The influence of ferro - paramagnetic transition and crystallization processes onto thermoelectric power is also observed.