Search

Graphical abstract Highlights • Synthesis of bulk La 0.7 Ba 0.3 Mn 1−x Al x O 3 (0 ≤ x ≤ 0.15) compounds with Al3+ substitution at Mn-site. • Significant crystal structural-relaxations in terms of bond-length, bond-angle and tolerance factor values. • Methodological investigation of magneto-transport and thermoelectric properties. • Enhanced magnetoresistance and determination of several other electronic-transport parameters that govern charge conduction. • Analysis of thermoelectric power via five degree polynomial fit and SPH/VRH polaron hopping mechanism. Abstract This report presents the structural, magnetoresistance, electrical and thermal transport properties of Aluminium substituted La 0.7 Ba 0.3 Mn 1−x Al x O 3 (0 ≤ x ≤ 0.15) compounds synthesized by solid state reaction method. To obtain crystallographic parameters, the X-ray diffraction patterns are fitted in R-3c space group with Rietveld refinement method. The resistivity and magneto-transport measurements are performed using standard four-probe assembly with and without magnetic fields. The peak resistivity ρ peak is noted at Metal-Insulator Transition temperature (T MI) and lowering in T MI is observed for higher concentrations of Al3+. The resistivity data have been analyzed in two parts. Firstly, in the metallic region below T MI the resistivity data is fitted with three degree polynomial. Secondly, in the semiconducting region above T MI data have been fitted with Variable Range Hopping (VRH) and Small Polaron Hopping (SPH) models. The Seebeck coefficients found to be positive throughout the temperature range (10 K–300 K) with holes as dominating charge carriers. Similar to the resistivity profile, in metallic region the thermo-power is explained with qualitative model based on diffusion, magnon-drag, phonon-drag and spin fluctuation contributions whereas the semiconducting region is explained with small polaron hopping model. [ABSTRACT FROM AUTHOR]

The parametric torque presents a promising recording mechanism for MRAM, complementing Spin Transfer Torque and Spin Orbit Torque, enabling magnetization reversal in a nanomagnet using a DC electrical current. Its resonance nature allows for optimization of magnetization reversal at a lower current, presenting an opportunity for a lower recording current and, therefore, for efficient and high-performance operation in modern MRAM technology. The in-plane magnetic field generated by spin accumulation serves as the driving force behind this torque. Experimental measurements of the current-induced in-plane magnetic field in the FeB nanomagnet reveal its magnitude to be around 40 Gauss at a current density of 25 mA/ μ m 2 , a value adequate for facilitating parametric magnetization reversal. The parametric torque is analytically calculated by solving the Landau–Lifshitz equation. Analytical calculations demonstrate its potential in advancing modern MRAM technology. • A novel resonance torque capable of magnetization reversal via DC electrical current is introduced. • Parametric torque, complementing Spin Transfer Torque and Spin Orbit Torque, enhances MRAM's recording capabilities. • Unlike Damp-Like and Field-Like torques, Parametric torque occurs only under specific identified conditions. • Experimental measurement of the spin-accumulation-induced magnetic field in a FeCoB nanomagnet is presented. • Parametric torque is analytically calculated via a solution of Landau–Lifshitz equation. [ABSTRACT FROM AUTHOR]

• Ca 4 Mn 3-x W x O 10 (x = 0, 0.05, 0.10) synthesised using a solid-state reaction technique. • Rietveld refinements of high-quality powder XRD show good convergences. • X-ray photoelectron spectroscopy show the mixed oxidation state of Mn cations. • Semiconducting behaviour of the samples is consistent with the VRH and SPH models. • Thermopower study reveals that all samples have a small polaron hopping mechanism. This report comprehensively investigates the crystal structure, magnetism, and transport properties of tungsten (W6+) substituted polycrystalline Ca 4 Mn 3-x W x O 10 (x = 0, 0.05, 0.1) compounds. The compounds were synthesized using the solid-state method and found to exhibit a single-phase orthorhombic structure confirmed by the Rietveld refinement. The substitution of (W6+) induces a change in the Mn octahedron and enhances the unit cell volume. The morphology indicates the crystalline nature of all the samples. The FTIR spectroscopic study revealed the position of the IR bands, which is highly sensitive to the oxidation state of Mn-ions. The shift to higher wavenumbers indicates reduced oxidation from Mn4+ to Mn3+ species. The appearance of the Mn4+ oxidation state in (x = 0) and the emergence of Mn3+ on W6+ substitution for (x = 0.05, 0.1) compounds are explored. The electrical resistivity plots revealed that compounds are semiconducting. The magnitude of resistivity decreases with W6+ substitution. The reported compounds exhibit a significant negative magneto-resistance towards lower temperatures. The compounds also demonstrate short-range ferromagnetic (FM) behavior attributed to the charge compensation effect's double exchange interaction (DE) connecting Mn4+ and Mn3+. The negative value of thermoelectric power (S) suggests the presence of charge carriers such as electrons, and the value of S first increased and then decreased in doped samples. The conduction in the studied compound is attributed to small polaron hopping. [ABSTRACT FROM AUTHOR]

The electric and thermal transport properties (electric resistivity ρ, magneto-resistance MR , Hall coefficient R H and anomalous Hall effect, thermal conductivity Κ and Seebeck coefficient S ) of the off-stoichiometric Ni 1.92 Mn 1.56 Sn 0.52 Heusler alloy were measured in a wide temperature and magnetic field range. The simultaneous measurement of several transport and magnetic properties offers a possibility to combine information arising from the received experimental results. The phonon and the charge carriers parts of complex temperature dependence of thermal conductivity K(T) were consistently separated using the Lorentz factor and temperature dependence of resistivity ρ (T) . The positive values of the Hall coefficient R H has been determined in martensite phase of the alloy at low temperatures. R H reaches zero value at temperature range where the so-called “paramagnetic gap” was observed and the negative value of R H was detected in austenite phase. Temperature dependence of the Hall coefficient R H (T) was used to derive both, the density and the mobility of charge carriers. The standard relations were used to describe the measured temperature dependence of the Seebeck coefficient. All the received result point to an important role of changes in electronic structure of the alloy in all the studied transport effects. A scenario of the complex behavior of the transport properties of the Heusler alloy based on a possible existence of an energy gap in electronic structure is discussed. [ABSTRACT FROM AUTHOR]

We report synthesis, structural details and electrical transport properties of topological insulator Bi 2 Te 3 . The single crystalline specimens of Bi 2 Te 3 are obtained from high temperature (950 °C) melt and slow cooling (2 °C/hour). The resultant crystals were shiny, one piece (few cm) and of bright silver color. The Bi 2 Te 3 crystal is found to be perfect with clear [00l] alignment. The powder XRD pattern being carried out on crushed crystals showed that Bi 2 Te 3 crystallized in R3̅m symmetry with a = b =4.3866(2) Å, c =30.4978(13) Å and γ =120°. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff position 6 c and of Te are (0, 0, 0) at Wyckoff position 3 a and at (0, 0, 0.2039(8)) at 6 c . Ambient pressure and low temperature (down to 2 K) electrical transport measurements revealed metallic behavior. Magneto transport measurements under magnetic field showed huge non saturating magneto resistance (MR) reaching up to 250% at 2.5 K and under 50 kOe field. Summarily, the short communication clearly demonstrates that Bi 2 Te 3 topological insulator exhibit non-saturating large positive MR at low temperature of say below 10 K. The non saturating MR is seen right up to room temperature albeit with much decreased magnitude. Worth mentioning is the fact that these crystals are bulk in nature and hence the anomalous MR is clearly an intrinsic property and not due to the size effect as reported for nano-wires or thin films of the same. [ABSTRACT FROM AUTHOR]

In the present paper we studied the structural, magnetotransport and thermopower properties of a series of polycrystalline La 0.7−x Sm x Ba 0.3 MnO 3 (0≤x≤0.2) compounds which were synthesized by conventional solid state reaction techniques. The Rietveld refinement of the X-ray diffraction pattern predicts the formation of single-phase compositions and doping of La 3+ by Sm 3+ ion converted the chemical structure form rhombohedral ( R-3C ) to orthorhombic ( Imma ) The scanning electron microscopy show clean smooth and densified structure images be a sign of good crystalline nature of the samples. The temperature dependent electrical resistivity is measured by standard four-probe method between 5 and 300 K exhibits Metal–Insulator Transition MIT which shows the decreasing trend with increasing Sm doping content and metallic state (TT p2 ) are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The application of magnetic field suppresses the resistivity in entire temperature range and with increasing the Sm 3+ content the samples showed very high magnetoresistance. The thermoelectric power (S) of the reported samples exhibit a crossover from positive to negative value and it increases in doped samples. The analysis of thermoelectric power data confirms the applicability of the small polaron hopping model in high temperature region and in low temperature fitted to an equation containing diffusion, magnon drag, phonon drag and electron-spin fluctuation term. An appropriate justification for the observed behavior is specified. [ABSTRACT FROM AUTHOR]

In intermetallic compounds RE Co 2 Si 2 ( RE =Pr and Nd), cobalt has been partially substituted by vanadium to obtain RE (Co 1− x V x ) 2 Si 2 ( 0 ≤ x ≤ 0.35 ). The parent compounds are antiferromagnetic below about 30 K due to the ordering of localized magnetic moments that are present only on rare-earth ions, cobalt being non-magnetic in the parent compounds. The present study demonstrates that in these compounds where 3 d and 4 f ions occupy different layers in the crystal structure, V substitution and subsequent lattice expansion results in the occurrence of inequivalent magnetic ions and complex interactions that lead to multiple magnetic transitions. At temperatures around 40–50 K, the temperature dependence of magnetization indicates a ferrimagnetic transition which is accompanied by a rapid decrease in the temperature dependence of resistivity. Below temperatures ∼30 K, the samples begin to show ferromagnetic-like behavior with the appearance of a coercive field and saturation in the magnetization at magnetic fields above ∼2 T. These two magnetic transitions are indicated also by prominent λ -like peaks in specific heat measurements. At around 10 K, a sharp drop in the resistivity indicates another magnetic transition which is followed by a rapid increase in coercive field with decrease in temperature. In a magnetic field of 9 T, the latter transition shifts to a lower temperature and that leads to a positive magnetoresistance. The onset of ferromagnetism at ∼30 K is accompanied with an exchange bias field which is observed for the first time in layered intermetallic compounds. The exchange bias field increases rapidly below the transition at ∼10 K and reaches ∼16% of coercive field at 2 K. [ABSTRACT FROM AUTHOR]

In the present work, the structural, magnetic, magneto-transport and thermoelectric properties of polycrystalline compounds of La 0.8− x Bi x Ca 0.2 MnO 3 (0≤ x ≤0.1) compounds are reported. Structure refinement using Rietveld method confirms that the samples are single phased and crystallize in rhombohedral structure with R-3C space group. Magnetic studies reveal that the pristine sample exhibits T C at 221 K and it shift towards lower temperature with Bi doping. Deviation of the temperature dependent of inverse susceptibility curves from the Curie–Weiss law confirms the existence of Griffiths-like phase. All the samples exhibit metal to insulator transition at temperature T MI , which is found to decrease with increase in Bi doping which is consistent with the magnetic studies. Magneto-resistance MR % data shows that its peak value increases with Bi-doping. The analysis of electrical resistivity data in the metallic region ( T < T MI ) suggests that the electron–electron scattering is predominant in this region whereas the insulating region ( T > T MI ) is well described using Small polaron hopping ( SPH ) and Mott's variable range hopping ( VRH ) models. Analysis of thermoelectric power data in the high temperature region suggests that the SPH mechanism is operative in this regime, while the analysis of low temperature data reveals that the electron–magnon scattering is dominant in the region. [ABSTRACT FROM AUTHOR]

For half metallic magnets, spin fluctuation is the same as charge fluctuation. The length scale is controlled by electron–electron interaction and is of the order of the screening length, typically of the order of an Angstrom whereas the ordinary spin diffusion length is of the order of 100 Å or more. We examine the eigenstates for charge and spin transport for systems close to half-metallicity. Due to the electron–electron interaction, the decay length of the eigenstate that corresponds to the longitudinal spin diffusion length is much reduced, consistent with recent experimental results. We explore the consequence of this. We find that there are two parameters that characterize half-metallicity and illustrate our results numerically with a simple model. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the magneto-transport of magnetite (Fe3O4) nanoparticles (MNPs) between Au nanogap electrodes (ANGEs) on surface-oxidized Si substrate. The MNP sizes are approximately 40nm and the 100nm thick magnetite thin film (which is formed of the MNP aggregation) was prepared between and around the ANGEs by use of the RF reactive magnetron sputtering method. The distance between the ANGEs and the bridge width of the ANGEs are approximately 50nm and 1.5μm, respectively. The ANGEs were produced by the tilted-angle-deposition method. The optical microscope, scanning electron microscope and atomic force microscope were used to observe the sample surface structure and morphology. To investigate the crystal structure and crystallinity of the MNPs, the X-ray diffraction measurement was performed. The electrical resistance and magneto-resistance ratio of the MNPs between the ANGEs were measured as a function of temperature. The magneto-transport mechanism is discussed on the basis of the spin dependent transport. [Copyright &y& Elsevier]

Abstract: 2MeV protons and 1MeV carbon ions are bombarded on highly oriented pyrolytic graphite (HOPG) samples and their electronic transport measurements are carried out in the presence of magnetic field. The Magneto-Resistance (MR) measurements show measurable hysteresis in the resistance value after ion beam irradiation for the in-plane magnetic field direction as well as for the out-of-plane field direction. The MR depends on the thickness of the flake and the method of its separation from the bulk HOPG. The results substantiate that the ferromagnetic coupling between the magnetic moments at the vacancy defect sites in HOPG sensitively depends on the average defect separation. The average defect separation range of 1.7–0.5nm allows only a part of the 40μm thick proton beam irradiated sample to go for ferromagnetic ordering. Similar conclusions are drawn from carbon ion irradiated HOPG flake. The irradiation increases the resistance of the flake as well. [Copyright &y& Elsevier]

Abstract: The perovskite manganite systems have been the materials of tremendous interest due to their strong correlation between structure, transport and magnetism. These materials in their single-crystal form show colossal magneto-resistance (CMR), but the applied fields are very high (∼1–5T). The polycrystalline samples do show high low-field magneto-resistance (LFMR), but good amount of control over particle sizes and grain-boundary distribution is required, which is well known but less realized in practical approaches. In this context, we report on synthesis and manipulation of polycrystalline La0.7Ba0.3MnO3 (LBMO) submicron powders using citric acid chelation. The Citrate-gel route is used to synthesize poly-dispersed LBMO powders which are subjected to citrate chelation for a duration of 0 (LB0) to 4h(LB4) . The samples show improved ordering in X-ray diffraction patterns. Raman spectroscopy scans indicate changed mode signatures due to the probable chelating process, which alters the surface morphology. X-ray photoelectron microscopy shows an evidence of fine citrate layer on the grain boundaries. Low temperature B–H curves exhibit fine hysteresis loops for all samples, while room temperature B–H curves shows paramagnetic response. Scanning electron microscopy images showed the formation of well arranged, connected, mono-dispersed grains of LB4 sample, as against polydispered LB0. The magneto-resistance (at H=100kOe) is seen to enhance for LB4 at its transition temperature (75%, as compared to LB0, where it is 60%), which can be attributed to the well-controlled inter-grain tunneling phenomenon and thin insulating regions in between, created due to citrate chelation, which probably enhances the scattering phenomenon and its susceptibility to applied fields. As citric acid is known to chelate Mn ions, it probably chelates the smaller LB particulate structure and leaves behind citrate-connected submicron grains of LBMO, which are seen to be well engineered. [Copyright &y& Elsevier]

Abstract: We investigated electrical- and magneto-resistance control in magnetite (Fe3O4) nanoparticle sinter (MNPS) by the regulation of heat treatment (HT) temperature. MNPS was produced from hematite (α-Fe2O3) nanoparticles (HNP’s) using a deoxidization reaction. The average size of HNP was 30nm, and HT was carried out between 400 and 800°C. X-ray diffraction, magnetization, electrical resistivity (ER), and magneto-resistivity (MR) measurements were performed at temperatures ranging from 5 to 300K. The ER and MR behaviors were considerably different at HT temperatures above and below ∼600°C. After HT below ∼600°C, ER followed the Mott-type variable-range-hopping conduction, and MR showed large values over a wide temperature range. After HT above ∼600°C, ER indicated a Verwey transition near 110K and MR showed small values, except in the vicinity of the Verwey transition temperature. Changing the HT temperature altered the coupling between adjacent magnetite nanoparticles (MNPs) and affected the crystallinity of MNPS. Below ∼600°C, ER and MR were dominated by grain-boundary conduction, while above ∼600°C they were determined by inter-grain conduction. The application of a magnetic field to the grain-boundary region, which had random localized spins, caused a large enhancement in MR. [ABSTRACT FROM AUTHOR]

Abstract: The structural magnetic and magneto-transport properties of double perovskite system Ba2− x Sr x FeMoO6 (0⩽x⩽1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe–Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba2FeMoO6 exhibits saturation magnetic moment value of 3.54μB/f.u. at 85K in a magnetic field of 6000Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73μB/f.u. and MR value of 7.08% (1T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail. [Copyright &y& Elsevier]

Abstract: A series of nano-crystalline Co x Ag100− x solid solutions have been prepared by NaBH4 reduction of the corresponding metal salts at room temperature in Ar gas flow. Alloys heat-treated at 600°C in Ar/H2 (5%) show the evolution of metastable fcc Co precipitates in Ag. Magnetic studies indicate that all the compositions are ferromagnetic with Curie temperatures >400K. For a nominal composition of Co60Ag40, heat-treated at 600°C, an effective negative magneto-resistance (MR) ratio of the order of ∼21% at 350K, at 2T is observed. This could arise from the influence of magnetic field on the electron–phonon scattering effects near to T c and to the spin-mixing scattering by magnons. [Copyright &y& Elsevier]

The frequency behaviour of the electrical properties of field-aligned CrO2 needle-shape powders has been investigated by the impedance spectroscopy method. The low frequencies R(f) increase with increasing θ, the angles between the applied current direction and the easy axis of the aligned samples. The specific frequency, of which a maximum -X(f) occurred, is varied towards the lower ones as θ increased. Analysis, based on classical electromagnetism as well as equivalent circuit method, has been performed to disclose the mechanism underlying for AC conductivity. [Copyright &y& Elsevier]

Pr1−xSrxCoO3−δ exhibits magnetoresistivity (MR) of up to 40% at 5 K with a strong hysteresis/memory effect. Magnetization measurements on Pr0.9Sr0.1CoO2.99 in an applied field of 100 Oe show that, as temperature decreases, the zero field-cooled (ZFC) and field-cooled (FC) magnetization curves branch clearly at 50 K, and a cusp appears in the ZFC branch at Tcusp∼20 K. Magnetization measurements in various fields between 100 and 10,000 Oe show that both the ZFC–FC branching temperature and, Tcusp, decrease with increasing field. The magnetization-field isotherms at 5 and 10 K show hysteresis loops typical of ferromagnets. No appreciable MR is seen in this compound at 50 K, i.e. at a temperature close to ZFC–FC branching temperature. At 20 K, negative MR of above 16% is observed without any hysteresis effect. We believe that the appearance of a ferromagnetic component at 5 K and 10 K (i.e. at temperatures below Tcusp) within the spin glass state of Co spins is responsible for both large MR and the prominent hysteresis/memory effect in MR. [Copyright &y& Elsevier]

• High rate of the Cu-substitution reduces the martensitic phase temperature. • It was found that magnetic field is very effective on martensitic phase transition. • In the case of low Cu-substitution, maximum MR% was obtained. • With application of the magnetic field, magnetic field induced phase transition takes place. Ni 50-x Cu x Mn 38 Sn 12 + B3% at (x = 0, 1, 3 and 5) melt spun ribbons have been fabricated by melt spinning technique. Structural, electrical and magnetoresistance properties of the ribbons were investigated in this study. It was identified that the austenite phase with the L2 1 type structure was formed in the ribbons, regardless of composition. Temperature dependence of resistance measurements exhibited the first order martensite transition in the ribbons. The largest negative magnetoresistance (~55%) was obtained at 262 K in the RB1 ribbon. Depending on the Cu-content and magnetic field, a noticeable shift of martensite transition temperature to low temperatures has been clearly observed. From magnetic field dependence of the resistance, it was seen that the resistances dropped sharply with the increase of the applied magnetic field and overlapped near 80 kOe, regardless of temperatures, which strongly indicates the magnetic field-induced martensite-austenite transition. [ABSTRACT FROM AUTHOR]

• Magnetic and electrical transport properties of as-cast compound Cr 2 CoAl were studied. • Below 20.5 K, the compound is a soft ferromagnetic material having very low magnetic moment. • Above 20.5 K, the presence of magnetic clusters within paramagnetic matrix is revealed. • Electrical resistivity indicates that Cr 2 CoAl is a metal. We report magnetic and electrical transport properties of polycrystalline as-cast compound Cr 2 CoAl having inverse Heusler like XA structure with B2 disorder. Temperature-dependent magnetization (M-T) under zero-field cooled (ZFC) and field cooled (FC) condition and field-dependent magnetization (M-H) studies suggest that this compound is a soft magnetic material below T c ~ 20.5 K having a very low magnetic moment as it is found that magnetization at 5 K under 50 kOe applied magnetic field is ~0.11μ B /f.u. Also, M-T data taken ZFC-FC condition under different applied magnetic fields and M-H data taken at 100 K and 300 K indicate that this compound may have magnetic clusters in paramagnetic matrix. Further analysis and temperature-dependent heat capacity measurement reveal paramagnetic to a short-range ordered ferromagnetic transition near T c ≈ 20.5 K and also reveal the presence of magnetic clusters within the compound. These magnetic clusters may arise because of B2 disorder in the compound. Temperature-dependent resistivity measurement confirms that the compound Cr 2 CoAl is metallic as it is found increasing with temperature. Nonlinearity in temperature dependency resistivity data, observed in low- temperature region, follows T2 dependency that generally comes because of electron–electron scattering. Magneto-resistance (MR) is also found to be positive throughout the temperature region from 8 K to 390 K. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic state diagram for spin current-induced magnetization dynamics is presented for an out-of-plane magnetized (perpendicular) polarizer and an in-plane magnetized (planar) free layer as obtained from macrospin simulations. The state boundaries are compared upon using a constant spin polarization factor with an angular-dependent spin polarization factor g(θ MP) as introduced by Slonczewski. While two critical boundaries remain unaffected by the angular dependence of the polarization, the transition from precession to an out-of-plane stable state is drastically shifted and shows a strong asymmetry with respect to the sign of the spin-polarized current. [Copyright &y& Elsevier]

• Improvement in M S and H C for the composite samples at room temperature. • Soft-hard magnetic phase was understood on the basis of exchange coupling interactions. • Enhanced magnetoresistance in a wide temperature range is observed. Nanocomposites of Lanthanum Strontium Manganite and Cobalt Ferrite with different weight percentages were prepared using the sol–gel method and sintered at 950 °C. Presence of constituent phases of La 0.67 Sr 0.33 Mn O 3 and CoFe 2 O 4 peaks were confirmed from X-ray diffraction and Fourier transform infrared spectroscopy studies. Hysteresis behaviour shows room ferromagnetism for the composite samples and their variation in saturation magnetization can be understood on the basis of competing effects between both the magnetic phases. Enhancement of squareness ratio and coercivity indicate the strengthening of exchange-coupling interaction due to closer proximity of hard and soft phases. Metallic state vanishes and resistivity increases with the incorporation of cobalt ferrite into lanthanum strontium matrix. An enhanced magnetoresistance in a wide temperature range is observed for 25% cobalt ferrite added sample and is ascribed to spin-polarized tunneling mechanism. Adiabatic small polaron hopping mechanism is used to explain the resistivity of the composites in the high temperature region. [ABSTRACT FROM AUTHOR]

• Ca 4 Mn 3 O 10 (CMO) undergoes a metal–insulator transition (MIT) at 70 K. • The MIT in CMO is accompanied by a structural effect. • Weak-ferromagnetic (WFM) behavior appears because of the slight structural distortion. • CMO indicate an unusual glassy magnetic behavior below the Néel temperature (T N) i.e., at MIT temperature. • The emergence of WFM at MIT temperature leads to the observed MR effect in CMO. • The switching of MR behavior from positive to negative at the MIT temperature is unique. Electronic phase separation is a frequent ingredient of the physics of manganites for which the colossal magnetoresistance (CMR) phenomenon is at debate. We investigate the switchable magnetoresistance (MR) effect of the Ruddelsden-Popper (RP) oxide Ca 4 Mn 3 O 10 (CMO), which shows a metal-to-insulator transition (MIT) at 70 K (T MIT). The static (DC) and dynamic (AC) magnetic susceptibilities of CMO indicate an unusual magnetic phase coexistence below the Néel temperature (T N) i.e., at T MIT , which we describe as a glassy magnetic behavior. Furthermore, by means of synchrotron X-ray diffraction, we observed a structural anomaly directly associated with the MIT. Hence, the onset of glassiness correlates with a slight structural distortion. Interestingly, CMO displays a large positive magneto-resistance (PMR) effect (up to 550% at 4 K) in the metallic state below T MIT , while a small negative magneto-resistance (NMR) effect (-3.5% at 112 K) in the insulating region above T MIT. At T MIT , the PMR switches to NMR behavior. PMR is probably induced via enhancing the exchange interaction by localization of itinerant moment resulting in formation of magnetic polarons, whereas NMR is possibly due to reduced electron-spin scattering. This appears to be a special type of magnetoresistance, different from regular observations, and may open a new avenue in searching for exotic phenomena in manganese-based CMR materials. [ABSTRACT FROM AUTHOR]

Abstract: We have synthesized La0.7Ba0.3MnO3 (LBMO):wt%Ag x and La0.7Sr0.3MnO3 (LSMO):wt%Ag x composites with x=0.0, 0.1, 0.2, 0.3 and 0.4 at different sintering temperatures of 1300 and 1400°C by solid-state reaction route. In our previous work [Awana et al. Solid State Commun. 140 (2006) 410] on La2/3Ca1/3MnO3 (LCMO):Ag x (x=0.0, 0.1, 0.2, 0.3, 0.4) composites, we reported about 12% temperature coefficient of resistance (TCR) for Ag0.4 samples near metal–insulator (MI) transition, which was explained on the basis of better grains connectivity. A sharp MI transition results in high TCR. Such high-TCR material can be used as a bolometer or infrared detector at room temperature. In the present work, it is shown that the TCR is improved with Ag addition for both LBMO:wt%Ag x and LSMO:wt%Ag x composites. In addition to improvement in TCR, high MR is also achieved in the vicinity of room temperature. [Copyright &y& Elsevier]

Abstract: In quasi-one-dimensional organic conductors such as (, , , etc.), the dips in the resistances along the most conducting axis and the inter-chain axis are observed at the so-called magic angles. Although the dips in have been explained in terms of the commensurate semi-classical orbits in the momentum space, the origin of the large dips in at magic angles is not clear. We study the angle-dependence of the conductivity along the most conducting axis, , by using a model neglecting electron correlation. We obtain that has small peaks at magic angles if we take account of the momentum-dependence of the Fermi velocity. [Copyright &y& Elsevier]