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In an article published in Advanced Functional Materials, researchers Jian Wang, Sicong Zhu, Jian Wu, and their colleagues discuss their work on electron delocalization engineering in 2D β‐AsP‐based materials. By constructing trace vacancies and doping sites, they were able to improve the physicochemical properties of these materials. This led to the creation of high-performance multisource logic devices that can be optically driven, electrically driven, or thermally driven. The researchers believe that their findings have the potential to contribute to advancements in waste energy recovery and other related fields. [Extracted from the article]

In this article, we report synthesis and magneto-transport analysis of Ni substituted Bi2Se3 crystals. Phase purity and crystalline growth are checked through X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Substitution of smaller Ni atoms is evident from lattice parameters which are apparently decreased with increased Ni concentration. Electron Dispersive X-ray analysis (EDAX) confirms presence of Ni atoms and Raman Spectroscopy measurements shows the presence of vibrational modes of Bi2Se3 with slight shift due to Ni substitution. Interestingly, Bi2Se3 tends to change its metallic phase to semiconducting phase with gradual Ni substitution. Magneto-resistance is also found to be drastically suppressed with Ni substitution due to semiconducting behavior of Ni substituted Bi2Se3. Magneto-conductivity of Ni substituted Bi2Se3 crystal is analyzed for the first time in this article by applying Hikami-Larkin-Nagaoka (HLN) model. [ABSTRACT FROM AUTHOR]

To study the effect of manganese non-stoichiometry at B-site, a series of manganites with compositional formula La 0.67 Sr 0.33 Mn 1±x O 3 (where x = 0, 0.05 and 0.1) was synthesized by oxalate precursor method. X-ray diffraction data confirm the rhombohedral structure of La 0.67 Sr 0.33 Mn 1±x O 3 along with minor phases of Mn 3 O 4. The average grain size is found to be 266 nm for x = 0 whereas its magnitude decreases with excess or deficiency in manganese concentration. An increase in the manganese non-stoichiometry leads to the coexistence of ferromagnetic and antiferromagnetic interactions. The effect of Mn 1±x on the magnetotransport properties could be understood on the basis of collective behaviour of magnetic spins, double exchange mechanism and ratio of Mn4+/Mn3+ ions. A crossover from negative to positive magnetoresistance behavior above metal-insulator transition temperature was observed for LSP-0.95 sample, whereas a positive magnetoresistance over the entire temperature region was noticed for LSP-1.10 sample. [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]

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 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]

Abstract In this paper, the resistivity of bilayer manganite LaSr 2 Mn 2 O 7 around the metal–insulator-like transition was systematically calculated as a function of temperature and applied magnetic field. A typical mathematical function (Gauss function) was used for fitting the experimental data. The theoretical values simulated in this work such as – metal–insulator transition temperature (T p) and maximum resistivity (ρ max) showed promising agreement with the experimental data. [ABSTRACT FROM AUTHOR]

We report the magneto-conductivity analysis at different temperatures under a magnetic field of up to 5 T of a well- characterized Bi2Te3 crystal. Details of crystal growth and various physical properties including high linear magneto-resistance are already reported by some of us. To elaborate upon the transport properties of Bi2Te3 crystal, the magneto-conductivity is fitted to the known Hikami-Larkin-Nagaoka (HLN) equation and it is found that the conduction mechanism is dominated by both surface-driven weak anti-localization (WAL) and the bulk weak localization (WL) states. The value of HLN equation coefficient (α) signifying the type of localization (WL, WAL or both WL and WAL) falls within the range of − 0.5 to − 1.5. In our case, the low-field (± 0.25 T) fitting of studied crystal exhibited a value of α close to − 0.86 for studied temperatures of up to 50 K, indicating both WAL and WL contributions. The phase coherence length (lφ) is found to decrease from 98.266 to 40.314 nm with increasing temperature. Summarily, the short letter reports the fact that bulk Bi2Te3 follows the HLN equation and quantitative analysis of the same facilitates to know the quality of studied crystal in terms of WAL to WL contributions and thus the surface to bulk conduction ratio. [ABSTRACT FROM AUTHOR]

Electrical resistivity studies reveal large granular effects in the superconductivity behaviour of the electron-doped cuprate, NdCeCuO, in polycrystalline form, much larger than their hole-doped counterparts. With the aim of investigating inter-granular coupling, as well as its variation with magnetic field and addition of Ag, AC susceptibility and magneto-resistance (MR) studies have been carried out on NdCeCuO + Ag composite system. A comparative study of the superconducting properties of the NdCeCuO + Ag composite system for Ag = 0, 5 and 15 wt%, including upper critical field [ H (0)], has been carried out and is presented. [ABSTRACT FROM AUTHOR]

In this article, iron nanowire is synthesized by reducing Fe2+ ion with excessive sodium borohydride in deionized aqueous solution. A kind of dimorphic magnetorheological gel is prepared by partial substitution of carbonyl iron particles with Fe nanowires. Several experimental devices based on the dimorphic magnetorheological gel were fabricated, and the magneto-resistance characteristics under a magnetic field of those devices are systematically tested to research the influence of the Fe nanowire on the conductivity of magnetorheological gel. The experimental results indicated that by adding a certain amount of Fe nanowire, the conductivity of the dimorphic magnetorheological gel can be greatly improved. Moreover, it can be seen that the conductivity of sample 4 (with 6 wt.% Fe nanowire) is increased by about 100 times than sample 1 (without Fe nanowire). The mechanism of Fe nanowire enhances the conductivity of the dimorphic magnetorheological gel, which is investigated by microstructure analysis. [ABSTRACT FROM AUTHOR]

In this letter, we report on the growth and characterization of bulk Bi Se single crystals. The studied Bi Se crystals are grown by the self-flux method through the solid-state reaction from high-temperature (950 °C) melt of constituent elements and slow cooling (2 ℃/h). The resultant crystals are shiny and grown in the [00l] direction, as evidenced from surface XRD. Detailed Reitveld analysis of powder X-ray diffraction (PXRD) of the crystals showed that these are crystallized in the rhombohedral crystal structure with a space group of R3m (D5), and the lattice parameters are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) Å. Temperature versus resistivity ( ρ− T) plots revealed metallic conduction down to 2 K, with typical room temperature resistivity ( ρ ) of around 0.53 m Ω-cm and residual resistivity ( ρ ) of 0.12 m Ω-cm. Resistivity under magnetic field [ ρ( T) H] measurements exhibited large + ve magneto-resistance right from 2 to 200 K. Isothermal magneto-resistance [ ρH] measurements at 2, 100, and 200 K exhibited magneto-resistance (MR) of up to 240 %, 130 %, and 60 %, respectively, at 14 T. Further, the MR plots are nonsaturating and linear with the field at all temperatures. At 2 K, the MR plots showed clear quantum oscillations at above say 10 T applied field. Also, the Kohler plots, i.e., Δ ρ/ ρ versus B/ ρ, were seen consolidating on one plot. Interestingly, the studied Bi Se single crystal exhibited the Shubnikov-de Haas (SdH) oscillations at 2 K under different applied magnetic fields ranging from 4 to 14 T. [ABSTRACT FROM AUTHOR]

We report on magneto-transport experiments in a high-quality sample of highly-oriented pyrolytic graphite (HOPG). Magneto-resistance and Hall resistivity measurements were carried out in magnetic inductions up to B = 9 T applied parallel to the c -axis at fixed temperatures between T =2 K and T =12 K. The sample was submitted to three subsequent irradiations with As ions. The implanted As contents were 2.5, 5 and 10 at% at the maximum of the distribution profile. Experiments were performed after each implantation stage. Shubnikov-de Haas (SdH) oscillations were observed in both the magneto-resistance and Hall-effect measurements. Analyses of these results with fast Fourier transform (FFT) lead to fundamental frequencies and effective masses for electrons and holes that are independent of the implantation fluences. The Hall resistivity at low temperatures shows a sign reversal as a function of the field in all implanted states. We interpret the obtained results with basis on a qualitative model that supposes the existence of an extrinsic hole density associated to the defect structure of our sample. We conclude that the As implantation does not produce a semiconductor-type doping in our HOPG sample. Instead, an increase in the extrinsic hole density is likely to occur as a consequence of disorder induced by implantation. [ABSTRACT FROM AUTHOR]

We present the relationships between the structure, magnetic properties and high-frequency magnetoresistance (MR) effect in melt-extracted CoFeBSi microwires subject to thermal annealing. In order to release residual stresses to improve the magnetic softness while retaining the good mechanical property of an amorphous material, microwire samples were annealed at different temperatures of 100°C, 200°C, 350°C, 400°C, and 450°C for 15 min. We have shown that relative to an as-cast amorphous microwire, annealing microwires at T = 100°C, 200°C, and 350°C improved both the magnetic softness and the MR effect, while an opposite trend was observed for the microwires annealed at T = 400°C and 450°C. We have observed a distinct difference in the frequency dependence of MR response ( ξ) for dc applied magnetic fields below and above the effective anisotropy field of the microwires. While the microwire annealed at 200°C shows the largest MR ratio (~580%) at 100 MHz, the highest value of ξ (~34%/Oe) has been achieved at 400 MHz for the microwire annealed at 350°C. These results indicate that the optimally annealed CoFeBSi microwires are attractive candidates for high-frequency sensor applications. [ABSTRACT FROM AUTHOR]

In this study, we showed the crystal structure, electric resistivity, Seebeck and Hall coefficients, magneto-resistance, and magnetic susceptibility of Pr 1 − x Ca x Ba 2 Cu 4 O 8 (x = 0.0, 0.02, and 0.05) are all relevant for our understanding of physical properties along CuO double chains. The lattice parameters of Ca substituted PrBa 2 Cu 4 O 8 remained almost invariant up to x = 0.05. Contrary to the Ca doping effect in the PrBa 2 Cu 3 O 7 − δ system, the significant increases in the Seebeck and Hall coefficients due to the Ca substitution indicate a decrease in the carrier number. The significant magneto-resistance effect in the parent sample (16% at 10 K) was significantly reduced down to 5% in the x = 0.05 composition. On the basis of the two types of carrier models, we discussed the influence of Ca substitution on the electrical transport and magneto-transport properties. • Metallic double chain based Pr/Ca124 compounds with low Ca substitution were successfully synthesized by a citrate pyrolysis method. • Despite Ca2+ replacement for Pr3+, the transport and magneto-transport properties of Pr/Ca124 suggested a significant reduction in the carrier number, which is in contrast with the Pr/Ca123 system. • Assuming that a carrier suppression due to the Ca substitution is attributed to the CuO double chains, our overall data for Pr/Ca124 are well explained based on the two-types of carrier transport model. [ABSTRACT FROM AUTHOR]

The composites with composition of (1− x )La 0.67 Sr 0.33 MnO 3 (LSMO)+( x )Ni 0.5 Zn 0.5 Fe 2 O 4 (NZFO) with x =0.0 (S1), 0.04 (S2), 0.07 (S3), 0.10 (S4), 0.30 (S5) and 1.0 (S6) were synthesized by solid-state reaction route. Structural study using Rietveld refinement of X-ray diffraction (XRD) pattern indicates a rhombohedrally-distorted structure (space group R 3 c ) for LSMO phase while to that NZFO compound crystallizes in cubic structure (space group Fd 3 m ). XRD patterns and microstructural analysis show that LSMO and NZFO phase exists independently in Ni 0.5 Zn 0.5 Fe 2 O 4 doped composites. The transport properties of the compositions x =0.0, x =0.04, and x =0.07 showed that NZFO phase improves the resistivity and shifts the metal–insulator transition temperature T MI towards lower temperature. The magnetoresistance (MR) of composite samples with x =0.04 and x =0.07 decreases monotonously from 200 to 300 K in a magnetic field of 8 T. At lower temperatures (~5 K), a sharp drop of negative MR at low fields ( H <1 T) has been observed followed by a slower varying MR at a comparatively high-field regime ( H >1 T) where MR is almost linear with applied magnetic field. Temperature dependence of resistivity for composites samples with x =0.04 and x =0.07 has been best fitted by small Polaron hopping (SPH) and variable range hopping models (VRH). [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]

A systematic investigation has been carried out on effect of Cr-doping on structural, magneto-resistance, magnetic and thermoelectric power properties of La 0.65 Ca 0.35 Mn 1− x Cr x O 3 compounds. Samples were prepared using conventional solid state reaction method. The XRD analysis using Rietveld refinement reveals that the samples are single phased. Temperature dependent electrical resistivity measurements show the existence of the expected metal–insulator transition ( T MI ) which is followed by a small hump at temperatures lower than T MI . With the application of magnetic field, resistivity of all the samples is found to decrease and T MI is observed to shift towards higher temperature. This is attributed to induced magnetic ordering of the localized t 2g spins and increased electron transfer integral between Mn 3+ /Mn 4+ via oxygen by the application of magnetic field. MR% is observed to increase with the increasing Cr concentration. Magnetic studies show that the Curie temperature, T C and magnetic moment decreases with Cr-content which is consistent with the electrical studies. Electrical resistivity and thermoelectric power data have been analyzed using theoretical models and both suggest that the small polaron hopping (SPH) model is operative in the high temperature insulating region for the entire series of samples. [ABSTRACT FROM AUTHOR]

A systematic study on the structural, electrical, magnetic and thermo-electric properties of La 0.8 Ba x Ca 0.2 − x MnO 3 (0 ⩽ x ⩽ 0.2) manganites is carried out in the present work. The samples have been prepared using solid state reaction technique. All the samples are single phased. It is seen that Ba-doping introduces a structural phase transformation viz. from rhombohedral to cubic system. Electric and magnetic studies respectively show that the metal–insulator transition temperature, T MI and Curie temperature, T C increase with Ba-content. Magneto-resistance (MR) data shows that it decreases with Ba-doping. Analyses of the electrical transport data in metallic region i.e. T < T MI shows that the electrical transport is governed predominantly by electron–electron scattering process. On the other hand, the adiabatic small polaron hopping (ASPH) model is appropriate in the high-temperature insulating range viz. T > T MI . We have used the electrical resistivity data in the entire temperature range (50–300 K) and analyzed using the phenomenological percolation model which is based on the phase segregation mechanism. We have analyzed the Seebeck coefficient data which reveals that the small polaron hopping mechanism is operative in high temperature regime and the low temperature region is examined by taking into account the impurity, electron–magnon scattering, and spin wave fluctuation terms. It is established that the electron–magnon scattering is dominating for the thermoelectric transport below T MI . [ABSTRACT FROM AUTHOR]

In this paper we study the magneto-resistance, i.e. the second-order term of the resistivity perturbed by a low magnetic field, of a three-dimensional composite material. Extending the two-dimensional periodic framework of [Mathematical Models and Methods in Applied Sciences 20(7) (2010), 1161-1177], it is proved through a H-convergence approach that the dissipation energy induced by the effective magneto-resistance is greater or equal to the average of the dissipation energy induced by the magneto-resistance in each phase of the composite. This inequality validates for a composite material the Kohler law which is known for a homogeneous conductor. The case of equality is shown to be very sensitive to the magnetic field orientation. We illustrate the result with layered and columnar periodic structures. [ABSTRACT FROM AUTHOR]

The carbon-based nanomaterial would push silicon aside and create a post- complementary metal oxide semiconductor world. In this work, we proposed and theoretically investigated an all-carbon spintronic device composed of C 18 cyclo molecule and two zigzag graphene nanoribbon (ZGNR) electrodes with two different sturdy connection modes. It is found that both structures have similar excellent spin-dependent properties. Adjusting the magnetization configuration of two electrodes to be anti-parallel, electrons in different spin states are filtered unidirectionally according to the sign of the applied bias voltage. The molecular junction exhibits a perfect dual spin filtering effect. Moreover, a huge magneto-resistance ratio was found in our propose junctions. The matching of symmetry type of the spin-polarized states in two ZGNR electrodes, as well as the states of C 18 in central region plays an important role in the occurrence of these effects. • All-carbon molecular device based on C 18 cyclo molecule were proposed. • Two types of stable connection models between C 18 cyclo and zigzag graphene nanoribbon electrodes were obtained. • The molecular junction exhibits a perfect dual spin filtering effect. • Present high magneto-resistance ratio over a wide bias voltage. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study of the magneto-resistance (MR), magneto-reactance (MX), and magneto-impedance (MI) effects in single and multiple glass-coated amorphous Co68B15Si10Mn7 microwires is reported. Our studies reveal that the MR, MX, and MI ratios and their corresponding magnetic field sensitivities strongly depend on the number of microwires in an array and on the distance between them. We find that increasing the number of microwires increases the MR and MI ratios and their field sensitivities (ηR and ηZ , respectively) but decreases the MX ratio and its field sensitivity (ηX ). A similar trend is observed for the frequency dependence of these parameters. Increasing the distance between the wires is also found to decrease the MR and MI ratios but increase the MX ratio of the array considerably. From a sensor application perspective, it is interesting to note that for the case of a single microwire, the ηX reaches a value as high as 960%/Oe at a frequency of 1MHz, which is about 192 times of the ηR or ηZ (∼5%/Oe), revealing the possibility of developing ultrahigh sensitivity magnetic field sensors based on the principle of the MX effect. [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]

We synthesized the polycrystalline manganite of La5/8Ca3/8MnO3 with three different manganese routes prepared through a solid state reaction method. The effects of the manganese route selection on the structure, electrical transport and magneto-transport properties were examined in this study. The samples were characterized using X-ray diffraction (XRD) and SEM to identify their structure and morphology. XRD analysis confirmed that all samples were in single phase with orthorhombic structure and belonged to the Pnma space group. The average grain sized samples with manganese route of Mn2O3 and MnCO3 had a grain size of 1.2-8.7 μm and 2-7.5 μm, respectively. For the MnO2 route, the sample had a small melt-like shape with higher porosity. The metal-insulator transition temperature, TMI, for LCMO (Mn2O3), LCMO (MnO2) and LCMO (MnCO3) samples were 270 K, 266 K and 258 K, respectively. All the samples showed negative magneto-resistance with significant increase in value near the TMI temperature. The highest CMR (colossal magneto-resistance) ratio was found in LCMO (Mn2O3), -22.06% at 270 K, followed by -16.69% for LCMO (MnO2) at 80 K, and 15.2% for LCMO (MnCO3) at 100 K in a 1 T magnetic field. [ABSTRACT FROM AUTHOR]

The exchange bias properties of nanopatterned thin films of Co, on top of which a native Co-oxide layer develops spontaneously, are studied by means of magnetic and magneto-resistance measurements. Both continuous and patterned films are investigated, the latter in the form of antidot arrays prepared with the self-assembling polystyrene nanospheres technique. The obtained antidot arrays are in the hexagonal close-packed configuration and cover a surface area of several square millimetres. Nanopatterned samples turn out to have a very good repeatability of their magnetic and magneto-resistive properties. The presence of a native oxide is responsible for the development of an exchange bias effect at temperatures below ~150 K, which has been reported both on hysteresis loops and on magneto-resistance curves; these consist of a superposition of an anisotropic magneto resistance (AMR) effect and a giant magneto-resistance (GMR)-like effect. The determination of the bias field by means of the two different sets of data is consistent and gives a complete picture of the phenomenology in this kind of nanopatterned magnetic systems. [ABSTRACT FROM AUTHOR]

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]

We compare methods for estimating the residual resistivity ratio (RRR) of high-purity niobium and investigate the effects of using different functional models. RRR is typically defined as the ratio of the electrical resistances measured at 273 K (the ice point) and 4.2 K (the boiling point of helium at standard atmospheric pressure). However, pure niobium is superconducting below about 9.3 K, so the low-temperature resistance is defined as the normal-state (i.e., non-superconducting state) resistance extrapolated to 4.2 K and zero magnetic field. Thus, the estimated value of RRR depends significantly on the model used for extrapolation. We examine three models for extrapolation based on temperature versus resistance, two models for extrapolation based on magnetic field versus resistance, and a new model based on the Kohler relationship that can be applied to combined temperature and field data. We also investigate the possibility of re-defining RRR so that the quantity is not dependent on extrapolation. [ABSTRACT FROM AUTHOR]

A general formula for the effective magneto-resistance in a two-dimensional heterogeneous conductor submitted to a low magnetic field is given through H-convergence. In the periodic case, it is proved that the dissipation energy due to the effective magneto-resistance is greater than or equal to the average of the energy due to the local magneto-resistance, and that the equality holds if and only if the local Hall coefficient is constant. This agrees with an anisotropic extension of the Kohler law in the framework of the ordinary magneto-resistance. The result is illustrated by the case of a two-phase rank-one laminate. [ABSTRACT FROM AUTHOR]

Abstract: We describe device models for spin injection, transport, and magneto-resistance in structures consisting of an organic semiconductor layer sandwiched between two ferromagnetic contacts. Carrier transport in the organic semiconductor is modeled with spin-dependent transport equations in drift-diffusion approximation. The effectiveness of spin-selective tunnel contacts on spin-polarized injection and magneto-resistance is examined on the basis of a simple analytical model. In agreement with earlier results, we find that spin injection from ferromagnetic metallic contacts into organic semiconductors can be greatly enhanced if (spin-selective) tunneling is the limiting process for carrier injection. We then explore the effects of the injected space charge and of spin relaxation in the semiconductor by comparing the results of a numerical calculation with the analytical model. For relatively thick organic semiconductor layers the injected space charge has strong effects on charge injection and, hence, on spin injection at high bias. Lastly, we consider a simple model for the bias dependence of the tunnel contacts and find that this effect may limit spin injection to relatively low currents. [Copyright &y& Elsevier]

A nano-sized oscillator for RF applications is presented which is based on two spintronic effects, the tunneling magnetoresistance (TMR) and the spin momentum transfer torque. The oscillation frequency is several GHz and can be tuned by both a DC bias current and an external DC magnetic field. High compactness, high tunability and full compatibility with standard CMOS process make this spin torque nano-oscillator (STNO) a promising candidate for future RF transceivers. The main issues to be addressed are spectral purity and output power. First measurements on a hybrid built connecting the STNO to a dedicated wideband amplifier show that today's performance in terms of power is close to but not yet compatible with telecommunication standard requirements. Using time domain analysis we show that frequency fluctuations are an issue for spectral purity. Frequency synthesis concepts based on STNOs are also discussed. [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]

A low-cost apparatus for measuring Hall effect and magnetoresistance is designed and built indigenously. This includes a 6.5 T superconducting magnet and a variable temperature sample holder assembly. A superinsulated liquid helium dewar with a low liquid helium boil-off rate is chosen as the low-temperature bath for doing magnetotransport measurements. A pair of high-Tc superconducting leads for energizing the magnet reduces the liquid helium consumption further and makes it economically beneficial, especially for laboratories with limited budget. The performance of the apparatus is tested over a wide range of temperatures (4.2 to 300 K) and fields up to 6.5 T. Reproducible magnetotransport data are obtained with excellent temperature and field stability. [ABSTRACT FROM AUTHOR]

In this paper, the first principle non-collinear transport calculation for Cu/Co(111) including interfacial spin-flipping was performed. We modeled spin-flipping at the interface by assuming a non-collinear magnetic structure with random magnetization orientation which satisfied the Gaussian distribution along the average magnetization direction. The relationship between spin-dependent conductance including interfacial spin-flipping and random magnetization orientation distribution width was obtained. For certain distribution width, our defined spin-flipping ratio coincides with the range of experimental spin-flipping probability P = 1-e-δ, where δ = 0.25±0.1. The magnetoresistance in the Co/Cu/Co spin-valve system including interfacial spin-flipping has also been calculated. [ABSTRACT FROM AUTHOR]

Abstract: We report results from structural, transport and magnetic measurements on polycrystalline Sr2− x Ba x FeMoO6 (, 1 and 2) half-metallic double perovskites. We find a large low field magneto-resistance (MR) of ∼−25% at 0.8T and 77K for samples that have high resistivities. We show that the low field tunneling MR can be modeled by assuming that there is a disordered region near the insulating grain boundaries as proposed by Serrate et al. It is the magnetization from this region rather than the bulk magnetization that determines the MR in polycrystalline samples. [Copyright &y& Elsevier]

This report presents the results of our activity during many years in the field of cryogenic thermometry and metrology applied to superconducting devices operating in the magnetic fields e.g. subsystems of accelerators and detectors. The equations to calculate the temperature shifts due to the magnetic fields for rhodium-iron, platinum, carbon-glass and carbon-aluminum oxide-TVO temperature sensors are given. [ABSTRACT FROM AUTHOR]

Abstract: Magneto-resistance ratios (MRR) were measured for (Fe3O4)1−x (CrO2) x granular junctions between 77K and 300K, where x is the volume ratio of CrO2 in the measured samples. Since the spin polarization coefficient P of conduction electrons is −1 in Fe3O4 and 1 in CrO2, these junctions are expected to show inverse tunneling magneto-resistance (TMR) effects. In 0.4⩽ x ⩽1, low resistive CrO2/Cr2O3/CrO2 junctions characterized MR behavior, while in x ⩽0.2, high resistive Fe3O4/(γ-Fe2O3 or Fe3O4+δ )/Fe3O4 junctions dominated the magnetic conduction. The inverse TMR effect only appeared at x =0.3 near the percolation threshold x c of CrO2/Cr2O3/CrO2 paths, where CrO2 particles, enclosed by Fe3O4 particles, reached a maximum number. The switching MRR behavior of x =0.3 was very sensitive to the magnetic field. Therefore the present system of (Fe3O4)0.7(CrO2)0.3 has the possibility of realizing a new half metallic spintronics device. [Copyright &y& Elsevier]

We measured an anisotropic magnetotransport that depends on directions of an in-plane field in a bilayer quantum Hall system. We found that the longitudinal resistance near the bilayer v = 1 quantum Hall state strongly varies when we changed an relative angle between the current and the in-plane field. It is a phenomenon peculiar to the bilayer v = 1 quantum Hail state, because this phenomenon does not appear in a monolayer system. [ABSTRACT FROM AUTHOR]

We systematically studied spin–orbit interaction in narrow wires with different wire widths, where the base material is a normal-type In0.75Ga0.25As/In0.75Al0.25As modulation-doped narrow-gap heterojunction. We used two different methods to make the wires and analyze their spin-dependent transports. As a first method, the wire width was defined by simply mesa-etching the samples on the same substrate. As a second method, we fabricated wire samples with side-gate. The wire width was changed by varying a voltage applied to the side-gate. For the determination of spin–orbit coupling constant, α, we measured magneto-resistance at 1.6 K. In the first method, α remained almost constant in the wires with various widths longer than 0.4 μm. However, in the second method, α increased with decreasing the wire width down to about 1 μm. The increase of α observed in the side-gate structure sample might rather be attributed to the effect of the lateral electric field by the side-gate, which could enhance the effect of the vertical electric field originally existing at the hetero-interface. [Copyright &y& Elsevier]

We study the magneto-resistance of a V-grooved GaAs quantum-wire field-effect transistor (QWR-FET) realized by selective growth of metalorganic vapor phase epitaxy. At low temperatures, the magneto-resistance of the wire shows reproducible fluctuations resulting from the quantum interference of electrons in the wire. The gate-voltage and temperature dependence of the conductance fluctuations are studied, and the latter reveal evidence for the robust phase coherence of electrons in the V-grooved QWR. [Copyright &y& Elsevier]

We present the first reports on nano-sized Co100−xCrx alloys (0&les;x&les;40), prepared by the sonochemical decomposition of respective metal-organic precursors. Samples heat-treated at 900 °C, exhibit a negative magneto-resistance ratio ranging from −1 to −4% at room temperature and at a field of 4 Tesla, owing to the tunneling conduction mechanism, while those heat treated at 300 °C show an MR of about ∼2% at 4.2 K and 300 K. Co100−xCrx nano-alloys heat-treated at 300 °C show an hcp phase, while 900 °C sintered samples show a pure hcp phase for x=20 and 30 and a pure hcp phase for x=40 samples. [Copyright &y& Elsevier]

(Co/ZnO/FeNi)2 multilayer heterostructures were fabricated by a multi-target magnetron sputtering system and photolithography. Their spin-dependent CPP (current perpendicular to plane) transport properties were investigated by magneto-transport measurement. An MR ratio of 3.3% is observed at 77 K, which decreased quickly with the increasing of ZnO thickness. No dependence of MR on the magnitude of the measuring current is observed, which indicated the MR is not caused by spin-dependent tunneling. [Copyright &y& Elsevier]

The orientation dependence of magneto-resistance behaviour for a single-walled carbon nanotube (SWCN) rope is reported. A clear delineation of behaviours is observed between applying a magnetic field perpendicular or parallel to the rope axis. For a perpendicular field, monotonic negative magneto-resistance is observed due to two-dimensional weak localisation within the rope. By contrast, for a parallel field, complicated oscillatory behaviour is observed due to the Altshuler–Aronov–Spivak effect around closed electron trajectories on discrete cylinders within the SWCN rope. A dominant oscillatory mode can be identified which corresponds to closed paths around the outer circumference of the SWCN rope. However, due to the composite filamentary nature of the rope, the overall oscillatory behaviour is rather complicated and can be classified as universal conductance fluctuations. With a backgate voltage applied to the sample, Coulomb blockade peaks are observed in the transport current with additional peak structure superimposed due to resonant tunnelling. We find an interesting effect whereby these peaks are suppressed in the presence of a magnetic field. [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]

• Large grain Ge rich polycrystalline SiGe thin film on glass at 350 °C using Al-induced layer exchange crystallization. • Degenerate p -type doping from residual Al atoms. • Weak anti-localization effect below 10 K in magnetoresistance. We report the low-temperature magneto-transport properties of a polycrystalline-SiGe thin film realized on glass at 350 ℃ via Al-induced layer exchange crystallization. The film exhibits a degenerate p -type behavior, and we observed evidence of weak-antilocalization (WAL) effect that manifests as an anomalous positive magnetoresistance (MR) below 10 K and weak magnetic fields (B) between ± 1 Tesla. While the spin–orbit coupling length is nearly constant at ~ 40 nm, the temperature dependence of phase-coherence length, which has a maximum value at 4 K (~131 nm), indicates hole-hole scattering as the predominant de-phasing mechanism. This result shows the degenerate Al doping causes the WAL effect in the present system. [ABSTRACT FROM AUTHOR]

• 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]