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Recently, a new type of exchange bias (EB) after zero-field cooling has attracted considerable interest mainly in bulk magnetic competing systems. Here, we use a detailed magnetotransport investigation to probe the ground state and zero-field cooled EB (ZEB) in Mn 50 Ni 41 Sn 9 ribbon. Both ZEB and field cooled EB were detected in magnetoresistance results consistent with magnetic measurement. A pure spin-glass ground state is proposed based on parabolic shape of low-field magnetoresistance combined with AC magnetization, memory effect. The appearance of ZEB is attributed to the field-induced nucleation and growth of ferromagnetic domains in the spin glass matrix forming unidirectional anisotropy at the interface. [ABSTRACT FROM AUTHOR]

We address the abnormal anisotropic magnetoresistance (AMR) reversal feature of half-metallic polycrystalline Fe 3 O 4 films occurring at a specific temperature. Experimental results revealed a positive to negative MR transition in the Fe 3 O 4 films at 264 K, which reflect the influence of additional domain wall scattering. These features was described by a correlation between domain wall resistance and inversion behavior of AMR with additional domain wall scattering factors. We further describe a possible model based on systematic structural and electrical measurements that employs a temperature-dependent domain wall width and spin diffusion length of the conducting electrons. This model allows for spin-flipping scattering of spin polarized electrons inside a proper domain width. [ABSTRACT FROM AUTHOR]

We investigated the structure and magneto-transport properties of magnetic junctions using a Co2Fe(Ga0.5Ge0.5) Heusler alloy as ferromagnetic electrodes and a Cu(In0.8Ga0.2)Se2 (CIGS) semiconductor as spacers. Owing to the semiconducting nature of the CIGS spacer, large magnetoresistance (MR) ratios of 40% at room temperature and 100% at 8 K were obtained for low resistance-area product (RA) values between 0.3 and 3 Ωµm2. Transmission electron microscopy observations confirmed the fully epitaxial growth of the chalcopyrite CIGS layer, and the temperature dependence of RA indicated that the large MR was due to spin dependent tunneling. [ABSTRACT FROM AUTHOR]

We investigate spin-current transport with an antiferromagnetic insulator NiO thin layer by means of the spin-Hall magnetoresistance (SMR) over a wide range of temperature in Pt/NiO/Y3Fe5O12 (Pt/NiO/YIG) heterostructures. The SMR signal is comparable to that without the NiO layer as long as the temperature is near or above the blocking temperature of the NiO, indicating that the magnetic fluctuation of the insulating NiO is essential for transmitting the spin current from the Pt to YIG layer. On the other hand, the SMR signal becomes negligibly small at low temperature, and both conventional anisotropic magnetoresistance and the anomalous Hall resistance are extremely small at any temperature, implying that the insertion of the NiO has completely suppressed the Pt magnetization induced by the YIG magnetic proximity effect (MPE). The dual roles of the thin NiO layer are, to suppress the magnetic interaction or MPE between Pt and YIG, and to maintain efficient spin current transmission at high temperature. [ABSTRACT FROM AUTHOR]

In this study, we present the experimental observation that polycrystalline Mn2+xFe1–xGa (x=–0.2, 0, 0.2, 0.4) compounds can be synthesized to be D019-type (Ni3Sn-type) hexagonal structure with space group P63/mmc. A giant exchange bias field up to 1.32 kOe was achieved in hexagonal Mn2FeGa alloy at 5K. A cluster glass state is confirmed by ac susceptibility measurement under different driving frequencies. Interestingly, robust horizontal and vertical shifts in magnetic hysteresis loop were simultaneously observed at 5K under high cooling field up to 90 kOe. The large exchange bias is originated from the large exchange anisotropy between cluster glass phase and ferrimagnetic matrix. The vertical shift is thought to be attributed to the incomplete reversal of frozen cluster spins. [ABSTRACT FROM AUTHOR]

The current-perpendicular-to-plane magnetoresistivity (CPP-MR)/ρc(B) is investigated in single crystal ruthenates Ca3(Ru1-xTix)2O7 (x=0.02). This material is naturally composed of ferromagnetic metallic bilayers (Ru,Ti)O2 separated by nonmagnetic insulating layers of Ca2O2, resulting in tunneling magnetoresistivity. Non-monotonic ρc(B) curves as well as the inverse spin valve effect are observed around the magnetic phase transition associating with the metal-to-insulator transition. A spin dependent tunneling model with alternate distribution of hard and soft magnetic layers [(Ru,Ti)O2] is proposed to explain the exotic CPP-MR behavior. This eccentric CPP-MR behavior highlights the strong spin-charge coupling in double-layered ruthenates and provides a potential material for spintronic devices. [ABSTRACT FROM AUTHOR]

The electrical properties of the neutron irradiated Si were analysed by means of the Hall effect and magnetoresistance temperature dependence. It was demonstrated that the electron mobility decreased with increasing the neutron fluence in a wide fluence range, and the microinhomogeneities in samples caused differences between the mobility values from the measured Hall and magnetoresistance effects. Exploiting the magnetoresistance mobility temperature dependence, the free carrier concentration dependence on temperature was analysed. It was found that the neutron irradiation introduced deep levels in the upper part of the bandgap, but their contribution decreased with increasing the neutron fluence - that is explained by more effective generation of acceptor type levels in the middle or lower part of the bandgap. The activation energy of the free carrier concentration did not follow the homogeneous semiconductor model, so the dark conductivity origin, that is related to the modified cluster model and cluster environment, was proposed. [ABSTRACT FROM AUTHOR]

Investigations on the pre-concentration of radionuclides (137Cs and plutonium isotopes) from fresh water on solid matrices are presented in this study. A particular focus was given to an innovative physico-chemical removal process such as adsorption of radionuclides from an aqueous medium on new type adsorbents, environmental-friendly materials. Sorption of the tested radionuclides from the lake water solution by environmental assays and synthetic sorbents was compared. Lake water was analyzed for main anions, micro- and macroelements, using ion and atomic absorption chromatography methods, respectively. Batch type and dynamic flow column laboratory experiments were performed. The sorption-desorption capacity of radionuclides by the tested sorbents was estimated based on the results of α- and γ-spectrometric measurements. According to the removal efficiency results, moss can be considered as the best sorbent for plutonium of the tested environmental-friendly sorbents, whereas the moss sorption capacity exceeded even that of the tested synthetic ones. The highest 137Cs removal efficiency from the lake water solution was obtained for granular activated carbon. Application of the dynamic flow method carried out in situ confirmed the reversibility of sorbed background 137Cs activity in the moss observed during the batch type experiments, and the method of the moss bed column turned to be unfit for the pre-concentration of 137Cs from the lake water. Application of a single moss bed column for the 137Cs and plutonium isotope pre-concentration for the first time carried out in situ allowed us to determine the activity concentration of 239,240Pu and 238Pu in the lake water - 4.87±0.98 and 0.67±0.21 mBq/m³, respectively. The reversible 137Cs and different plutonium sorption in the moss apparently indicates different binding properties of these radionuclides to the moss, therefore further investigations on this issue are foreseen. Darbe pristatomi radionuklidų (137Cs ir plutonio izotopų) sukoncentravimo iš gėlo vandens kietose matricose tyrimai. Ypatingas dėmesys skirtas inovatyviam fizikiniam-cheminiam radionuklidų pašalinimo iš vandeninės terpės procesui - adsorbcijai, naudojant naujo tipo sorbentus, gamtines medžiagas. Tyrimai atlikti į ežero vandens tirpalą įterpus 137Cs ir 236Pu izotopus. Ežero vandenyje nustatyti pagrindiniai anijonai, mikro ir makroelementai, pritaikant jonų ir atominės absorbcijos chromatografijos metodus. Radionuklidų sorbcijos-desorbcijos geba buvo įvertinta pagal α- ir γ- spektrometrinių matavimų duomenis. Gamtinių ir sintetinių sorbentų sorbcinė geba buvo palyginta taikant statinius (purtant) ir dinaminius kolonėlių (pratekant) metodus. Pagal pašalinimo iš tirpalo efektyvumo rezultatus, iš visų tirtųjų gamtinių medžiagų, išskyrus molį, samanos gali būti laikomos geriausiu plutonio sorbentu, o samanų sorbcinė geba buvo didesnė net už sintetinius sorbentus. Didžiausiu 137Cs iš ežero vandens tirpalo pašalinimo efektyvumu pasižymėjo granuliuotos aktyvintos anglies kolonėlės. Pritaikius dinaminį metodą, filtruojant per samanų kolonėles natūralų ežero vandenį in situ, pasitvirtino statiniu metodu laboratorijoje gauti rezultatai apie 137Cs grįžtamąją sorbciją samanose. Priešingai negu 137Cs, toje pačioje samanų kolonėlėje plutonio izotopai buvo sorbuojami iš ežero vandens. Pagal samanų kolonėlėje akumuliuotų radionuklidų α-spektrometrinius matavimus po radiocheminės analizės nustatyta, kad 239, 240Pu aktyvumo koncentracija ežero vandenyje yra 4,87±0,98 mBq/m³, o 238Pu - 0,67±0,21 mBq/m3. Gauti skirtingi 137Cs ir plutonio sorbcijos rezultatai, naudojant samanas kaip sorbentą, nurodo skirtingas šių radionuklidų prisijungimo prie samanų savybes, todėl numatomi tolimesni adsorbcijos tyrimai. [ABSTRACT FROM AUTHOR]

Using anisotropic magnetoresistance in a multi-probe configuration and local heating with a scanning laser, we investigate the magnetization reversal of individual permalloy (Py) and CoFeB nanotubes with spatial resolution. Nanocrystalline Py and amorphous CoFeB nanotubes are found to reverse via domain wall movement and chirality switching, respectively. Our experiments provide an understanding of the role of microstructure and magnetic anisotropy in the switching of ferromagnetic nanotubes at room temperature. [ABSTRACT FROM AUTHOR]

Mixed-valence manganites gain increasing attentions thanks to their extraordinary properties including half-metallicity and colossal magnetoresistive response, rendering them ideal candidate for oxide spintronics applications. Oxygen vacancies in oxides have been approved to be important functional defects and are effective to manipulating their multifunctional properties. To gain a deep insight into the roles of oxygen vacancies on regulating the atomic structure and electronic properties of the mixed-valence manganites, two high-quality epitaxial La2/3Sr1/3MnO3 films around a critical point (without/with oxygen vacancies) were designed and fabricated. From the experiments and theoretical calculations, it was found that the oxygen vacancies induce a weakening of Mn-O-Mn hybridized bond and an increase of concentration of Mn3+ ions, impair the double exchange between Mn3+ and Mn4+, and therefore lead to the transition from metal to insulator and the degraded magnetic properties. Our finding demonstrates a practical approach to tune the magnetic and transport properties of oxide thin films by precisely controlling the oxygen vacancies for high performance spintronics applications. [ABSTRACT FROM AUTHOR]

We characterized the interfaces of heterostructures with different stack sequences of La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) and BFO/LSMO using TEM revealing sharp and rough interfaces, respectively. Magnetometry and magnetoresistance measurements do not show a detectable exchange bias coupling for the multistack with sharp interface. Instead, the heterostructures with rough and chemically intermixed interfaces exhibit a sizable exchange bias coupling. Furthermore, we find a temperature-dependent irreversible magnetization behavior and an exponential decay of coercive and exchange bias fields with temperature suggesting a possible spin-glass-like state at the interface of both stacks. [ABSTRACT FROM AUTHOR]

Experiments are performed on mesoscopic nonlocal lateral spin valves with aluminum channels and Permalloy electrodes. Four-terminal magnetoresistance and Hanle measurements characterize the spin accumulation with results that compare well with published work. Three-terminal Hanle measurements of the Permalloy/aluminum (Py/Al) interfaces show bell-shaped curves that can be fit to Lorentzians. These curves are three orders of magnitude larger than the spin accumulation. Using anisotropic magnetoresistance measurements of individual Permalloy electrodes, we demonstrate that the three-terminal measurements are dominated by anisotropic magnetoresistance effects unrelated to spin accumulation. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of bent [100] α-Fe nanowires show the nucleation of twins and nanoscale interfaces that lead to pseudo-elasticity during loading/unloading cycles. The new type of interfaces along {110} stems from the accumulation of individual <111>/{112} twin boundaries and stores high interfacial energies. These nonconventional interfaces provide a large part of the driving force for shape recovery upon unloading, while the minimization of surface energy is no longer the dominant driving force. This new pseudo-elastic effect is not much affected by surface roughness, and can be extended over a wide range of wire diameters, if the sample is seeded with conventional twin boundaries, which will transform to the desired {110} interfaces under bending. [ABSTRACT FROM AUTHOR]

Three-dimensional topological insulators and topological crystalline insulators represent new quantum states of matter, which are predicted to have insulating bulk states and spin-momentum-locked gapless surface states. Experimentally, it has proven difficult to achieve the high bulk resistivity that would allow surface states to dominate the transport properties over a substantial temperature range. Here we report a series of indium-doped Pb1-xSnx vTe compounds that manifest huge bulk resistivities together with evidence consistent with the topological character of the surface states for x ≳ 0.35, based on thickness-dependent transport studies and magnetoresistance measurements. For these bulk-insulating materials, the surface states determine the resistivity for temperatures beyond 20 K. [ABSTRACT FROM AUTHOR]

On a set of 12 bulk and highly pure [residual resistance ratio (RRR) up to 6000] iron single crystals with different crystallographic orientation and on polycrystalline material the "hidden" basic resistivity p(T,B→ 0) and magnetoresistive effects (anisotropic magnetoresistance, longitudinal and transverse Lorentz resistance) are quantitatively disentangled. The temperature-dependent basic resistivity for T ⩽30 K follows a Δp(T,B→0) = aT 2 + bT5 law, proving that electron-electron and electron-phonon scattering (with a resistive Debye temperature Θ R ≃ 450 K) are dominant also in iron, similar to nonferromagnetic transition metals. Here the crystal-orientation dependence of the intrinsic longitudinal magnetoresistance in the single-domain state could be quantitatively evaluated in accordance with the symmetry of the Fermi surface. The transverse magnetoresistance (TMR) turns out to be the sum of the so-called "two-band conduction term" and the unboundedly growing TMR term in compensated metals. It is proven that the second term is not restricted to the high-field limit (as usually discussed up to now) but acts down to lowest TMR or ωc r values. This conclusion is verified by TMR measurements on highly pure molybdenum single crystals (RRRs 100000). Supported by Kerr microscopy, a small positive domain wall resistance (DWR) could be isolated from the dominating negative DWR in the multidomain state of iron, resulting in a relation of larger than 5:1 for the electrons to pass a domain wall with spin tracking compared to scattering with spin conservation. [ABSTRACT FROM AUTHOR]

The longitudinal pxx(B,T) and Hall pxy(B,T) magnetoresistances in n-InGaAs/GaAs heterostructures with a single quantum well are studied experimentally before and after IR illumination in the quantum Hall regime in magnetic fields B = 0-12 T and at temperatures T = 0.4-4.2 K. The temperature dependence of the width of quantum Hall plateau-plateau transitions is analyzed in terms of a twoparameter scaling theory. [ABSTRACT FROM AUTHOR]

The mixed-chalcogenide compound TIBiSSe realizes a three-dimensional (3D) Dirac semimetal state. In clean, low-carrier-density single crystals of this material, we found Shubnikov-de Haas oscillations to signify its 3D Dirac nature. Moreover, we observed very large linear magnetoresistance (MR) approaching 10 000% in 14 T at 1.8 K, which diminishes rapidly above 30 K. Our analysis of the magnetotransport data points to the possibility that the linear MR is fundamentally governed by the Hall field; although such a situation has been predicted for highly inhomogeneous systems, inhomogeneity does not seem to play an important role in TIBiSSe. Hence, the mechanism of large linear MR is an intriguing open question in a clean 3D Dirac system. [ABSTRACT FROM AUTHOR]

We present magnetoresistance measurements on La 0.7 Sr 0.3 MnO 3 /YBCO/La 0.7 Sr 0.3 MnO 3 /YBCO (L1/Y1/L2/Y) heterostructure. The Ll/Y1/L2/Y spin valve shows large magnetoresistance peaks in coercive field at temperatures below the onset of the superconducting transition. The rotation in parallel magnetic field demonstrates a change of magnetoresistance; simultaneously the transition temperature to superconducting state T c0 ( H =450 Oe, β ) exhibits nonmonotonic dependence due to change of noncolinearity of magnetic moments of LSMO layers. Nonmonotonic change of the transition temperature as a function of angle is interpreted as a signature of generation of the triplet component superconducting phase in the Ll/Y1/L2/Y heterostructure. [ABSTRACT FROM AUTHOR]

The enhanced thermopower of the correlated semiconductor FeSi is found to be robust against the sign of the relevant charge carriers. At T≈70 K, the position of both the high-temperature shoulder of the thermopower peak and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient ν assumes a large maximum and the Hall mobility μH diminishes to below 1 cm2/V s. These cause the dimensionless ratio ν/μH—a measure of the energy dispersion of the charge scattering time τ(ε)—to exceed that of classical metals and semiconductors by two orders of magnitude. Concomitantly, the resistivity exhibits a hump and the magnetoresistance changes its sign. Our observations hint at a resonant scattering of the charge carriers at the magnetic crossover, imposing strong constraints on the microscopic interpretation of the robust thermopower enhancement in FeSi. [ABSTRACT FROM AUTHOR]

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices. [ABSTRACT FROM AUTHOR]

We perform magnetoresistance (MR) measurements to experimentally track magnetic domain wall pinning/depinning process in L-shaped Permalloy (Py) nanostructures with widths in the range 50–400 nm. We demonstrate that the field interval between the pinning/depinning events increases with the reduction of the nanowire width. The most reproducible measurements are obtained from the narrowest devices. MR measurements reveal that the stochastic contribution to pinning/depinning processes is higher when the applied field is oriented symmetrically with respect to both arms of the device. The interpretation of experimental results is supported by micromagnetic simulations. [ABSTRACT FROM AUTHOR]

The c-axis orientation YBa2Cu3Oδ thin film was prepared directly on MgO substrate by the pulse laser deposition. The thickness of the film is 170 nm. The superconducting critical temperature is Tc50% = 87:5 K and the width of superconducting transition is ΔT = 1:8 K. The temperature dependences of magnetoresistance were measured up to 90 kOe. The widths of the transition to the superconducting state versus applied magnetic field were derived and they were fitted using the formula: ΔT = CHm +ΔT0. The irreversibility fields as a function of temperature were obtained and fitted by the de Almeida and Thouless-like equation: Hirr = Hirr0(1-T=Tc0)n. The irreversibility field at the liquid nitrogen temperature was calculated and it is Hirr = 43:8 kOe when the applied magnetic field is parallel to the c-axis. [ABSTRACT FROM AUTHOR]

Basing our considerations on magnetic equation of state applied to the description of magnetic systems of confined geometry we developed the model of calculations of the electrical resistivity for metallic multilayers. It was shown that in the transport of charge in ferromagnetic material d-electrons play an important role. The key parameters in the presented model are: the width of the electron energy band and the shift of the energy level for two spin orientations as well as the Fermi energy and size of the sample (the thickness of magnetic and nonmagnetic layers and the total number of layers). The presented results of calculations for temperature dependence of magnetoresistance are in qualitative agreement with the available experimental data. The model calculations introduced in this paper can be applied to current-in-plane geometry as well as to current-perpendicular-to-plane geometry. The calculations are valid within the limitations of the resistor network model. [ABSTRACT FROM AUTHOR]

We put forward a theory of the weak localization in two-dimensional graphene layers which explains an experimentally observable transition between positive and negative magnetoresistance. Calculations are performed for the whole range of a classically weak magnetic field with an account on intervalley transitions. Contribution to the quantum correction which stems from closed trajectories with few scatterers is carefully taken into account. We show that intervalley transitions lead not only to the transition from weak antilocalization to the weak localization, but also to the nonmonotonous dependence of the conductivity on the magnetic field. [ABSTRACT FROM AUTHOR]

We report magnetoresistance measurements on thin Pt bars grown on epitaxial (001) and (111) CoFe2O4 (CFO) ferrimagnetic insulating films. The results can be described in terms of the recently discovered spin Hall magnetoresistance (SMR). The magnitude of the SMR depends on the interface preparation conditions, being optimal when the Pt/CFO samples are prepared in situ, in a single process. The spin-mixing interface conductance, the key parameter governing SMR and other relevant spin-dependent phenomena, such as spin pumping or spin Seebeck effect, is found to be different depending on the crystallographic orientation of CFO, highlighting the role of the composition and density of magnetic ions at the interface on spin mixing. [ABSTRACT FROM AUTHOR]

We present the quantum-mechanical calculation of the angular dependence of interlayer conductivity σzz(θ) in a tilted magnetic field in quasi-two-dimensional (quasi-2D) layered metals. Our calculation is applicable for arbitrary density of electron states and shows that the shape of Landau levels (LLs) is important for this angular dependence. We derive simple analytical formulas for σzz(θ) in the particular cases of Gaussian and dome-shaped LLs. Since in strongly anisotropic quasi-two-dimensional metals in a high magnetic field the LL shape is closer to dome-like or Gaussian, this analytical formula replaces the traditionally used one, derived for Lorentzian LL shape. The amplitude of angular magnetoresistance oscillations (AMRO) is considerably stronger for the dome-like or Gaussian than for the traditionally used Lorentzian LL shape. The ratio ozz(θ = 0)/σzz(θ→ ±90°) is also several times smaller for the Lorentzian LL shape at the same LL width. The field dependence of σzz(θ → ±90°) provides useful information about the electron mean free time. AMRO and Zeeman energy splitting lead to a spin current. For typical organic metals and for a medium magnetic field of 10 T this spin current is only a few percent of the charge current. However, the spin current may almost reach the charge current for special tilt angles of the magnetic field. The spin current has strong angular oscillations, which are phase-shifted as compared to the usual AMRO. [ABSTRACT FROM AUTHOR]

We study the quantum interference correction to the conductivity in HgTe quantum wells using the Bemevig-Hughes-Zhang model. This model consists of two independent species (blocks) of massive Dirac fermions. We describe the crossover between the orthogonal and symplectic classes with increasing the carrier concentration and calculate, respectively, weak localization and antilocalization corrections in the absence of the block mixing and assuming the white-noise disorder within each block. We have calculated the interference-induced magnetoresistance in a wide interval of magnetic fields, in particular, beyond the diffusion regime. Remarkably, each Dirac cone taken separately gives a linear contribution to the low-field magnetoresistance, which turns out to be asymmetric in magnetic field B. We present an interpretation of this result in terms of the Berry-phase formalism. The contributions of the two blocks are related to each other by replacing B to - B, so that the total magnetoresistance is symmetric and parabolic in the limit B → 0. However, in some range of parameters, field dependence turns out to be strongly nonmonotonous. We also demonstrate that block mixing gives rise to additional singular diffusive modes which do not show up in the absence of mixing. [ABSTRACT FROM AUTHOR]

We study the temperature dependence of the spin Hall magnetoresistance (SMR) in yttrium iron garnet/platinum hybrid structures via magnetization orientation dependent magnetoresistance measurements. Our experiments show a decrease of the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR to the spin transport properties of the normal metal, we interpret our data in terms of a decrease of the spin Hall angle in platinum from 0.11 at room temperature to 0.075 at 10 K, while the spin diffusion length and the spin mixing conductance of the ferrimagnetic insulator/normal metal interface remain almost constant. [ABSTRACT FROM AUTHOR]

The article discusses a research related to the investigation of fabrication and transport properties of spin gapless Heusler alloy Mn2CoAl films prepared on thermally oxidised silicon (Si) substrates by deposition using magnetron sputtering. Topics discussed include films deposition at 673 Kelvin, analysis of resistivity, anomalous Hall conductivity and linear magnetoresistance and use of energy-dispersive X-ray and X-ray photoelectron spectroscopy for elements characterization.

We validate the linear dispersion relation (Dirac cone) on the surface of a single Bi2Te3 nanowire via a combination of field-effect and magnetoresistance measurements by which we unambiguously prove the topological insulator nature of the nanowire surface states. Moreover, we show that the experimentally determined carrier concentration, mobility, and cyclotron mass of the surface states are in excellent agreement with relativistic models. Our method provides a facile way to identify topological insulators that too small for angle-resolved photoemission spectroscopy. [ABSTRACT FROM AUTHOR]

We report the magnetic and magnetotransport properties of (In0.985Nd0.015)2O2.89 thin films grown by pulse laser deposition. The clear magnetization hysteresis loops with the complementary magnetic domain structure reveal the intrinsic room temperature ferromagnetism in the as-prepared films. The strong sp-f exchange interaction as a result of the rare earth doping is discussed as the origin of the magnetotransport behaviours. A positive magnetoresistance (~29.2%) was observed at 5K and ascribed to the strong ferromagnetic sp-f exchange interaction in (In0.985Nd0.015)2O2.89 thin films due to a large Zeeman splitting in an external magnetic field of 50 KOe. [ABSTRACT FROM AUTHOR]

Magnetic and resistive anisotropies have been studied for the La0.325Pr0.3Ca0.375MnO3 films with different thicknesses grown on low symmetric (011)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 substrates. In the magnetic and electronic phase separation region, a colossal anisotropic resistivity (AR) of ~105% and an anomalous large anisotropic magnetoresistance can be observed for 30 nm film. However, for 120 nm film, the maximum AR decreases significantly (~2×10³%) due to strain relaxation. The colossal AR is strongly associated with the oriented formation of magnetic domains, and the features of the strain effects are believed to be useful for the design of artificial materials and devices. [ABSTRACT FROM AUTHOR]

Magnetophotoluminescence and magnetotransport were studied in a GaAs/AlGaAs triple quantum well. Oscillations of the photoluminescence intensity observed in tilted magnetic fields were found to correspond to the interlayer tunneling quantum Hall gap collapses detected in magnetoresistance measurements and predicted to occur in tilted magnetic fields. The obtained experimental data were shown to agree well with the theory developed for double quantum wells. This implies that the observed quantum Hall gap collapses are mostly caused by the tunneling between a pair of quantum wells. Our results reveal spectroscopic evidence of the quantum Hall gap collapses. Indications of interlayer correlation effects influencing a character of the inter-Landau-level gaps were found. [ABSTRACT FROM AUTHOR]

We report the observation of spin-dependent quantum well (QW) resonant tunneling in textured CoFeB free layers of single MgO magnetic tunnel junctions (MTJs). The inelastic electron tunneling spectroscopy spectra clearly show the presence of resonant oscillations in the parallel configuration, which are related with the appearance of majority-spin Δ1 QW states in the CoFeB free layer. To gain a quantitative understanding, we calculated QW state positions in the voltage-thickness plane using the so-called phase accumulation model (PAM) and compared the PAM solutions with the experimental resonant voltages observed for a set of MTJs with different CoFeB free layer thicknesses (tfl =1.55, 1.65, 1.95, and 3.0nm). An overall good agreement between experiment and theory was obtained. An enhancement of the tunnel magnetoresistance with bias is observed in a bias voltage region corresponding to the resonant oscillations. [ABSTRACT FROM AUTHOR]

Abstract: The magnetization characteristic in a Permalloy thin strip is investigated by electrically measuring the anisotropic magnetoresistance and ferromagnetic resonance in in-plane and out-of-plane configurations. Our results indicate that the magnetization vector can rotate in the film plane as well as out of the film plane by changing the intensity of external magnetic field of certain direction. The magnetization characteristic can be explained by considering demagnetization and magnetic anisotropy. Our method can be used to obtain the demagnetization factor, saturated magnetic moment and the magnetic anisotropy. [Copyright &y& Elsevier]

This article presents the current puzzling controversy between theory and experimental results concerning the mechanisms leading to spin relaxation in graphene-based materials. On the experimental side, it is surprising that regardless of the quality of the graphene monolayer, which is characterized by the carrier mobility, the typical Hanle precession measurements yield spin diffusion times (τs) in the order of τs ∼ 0.1–1 ns (at low temperatures), which is several orders of magnitude below the theoretical estimates based on the expected low intrinsic spin–orbit coupling in graphene. The results are weakly dependent on whether graphene is deposited onto SiO2 or boron-nitride substrates or is suspended, with the mobility spanning 3 orders of magnitude. On the other hand, extraction form two-terminal magnetoresistance measurements, accounting for contact effects results in τs ∼ 0.1 µs, and corresponding diffusion lengths of about 100 µm up to room temperature. Such discrepancy jeopardizes further progress towards spin manipulation on a lateral graphene two-dimensional platform. After a presentation of basic concepts, we here discuss state-of-the-art literature and the limits of all known approaches to describe spin transport in massless-Dirac fermions, in which the effects of strong local spin–orbit coupling ceases to be accessible with perturbative approaches. We focus on the limits of conventional views of spin transport in graphene and offer novel perspectives for further progress. [ABSTRACT FROM AUTHOR]

By using nonequilibrium Green's functions in combination with the density functional theory, we investigate the spin-dependent transport properties in a Fe-porphyrin-like carbon nanotube spintronic device. The results show that magnetoresistance ratio is strongly dependent on the magnetic configuration of the Fe-porphyrin-like carbon nanotube. Under the application of the external magnetic field, the magnetoresistance ratio of the device can be increased from about 19% to about 1020% by tuning the magnetic configuration in the device. Our results confirm that the magnetic configuration is a key factor for obtaining a high-performance spintronic device. [ABSTRACT FROM AUTHOR]

Abstract: We report new experimental data regarding the transverse magnetoresistance measured in a family of thin gold films of different thickness with the electric field E oriented perpendicular to the magnetic field B (both fields contained within the plane of the film), as well as a theoretical description of size effects based upon a solution of Boltzmann Transport Equation. The measurements were performed at low temperatures T (4K≤ T ≤50K) under magnetic field strengths B (1.5T≤ B ≤9T). The magnetoresistance signal can be univocally identified as arising from electron-surface scattering, for the Hall mobility at 4K depends linearly on film thickness. The magnetoresistance signal exhibits a marked thickness dependence, and its curvature as a function of magnetic field B varies with film thickness. The theoretical description of the magnetic field dependence of the magnetoresistance requires a Hall field that varies with the thickness of the film; this Hall field is tuned to reproduce the experimental data. [Copyright &y& Elsevier]

We investigated quantum confinement effects in Bi anti-dot thin films grown on anodized aluminium oxide templates. The pore wall widths (wBi) and thickness (t) of the films were tailored to have values longer or shorter than Fermi wavelength of Bi (λF=∼40 nm). Magnetoresistance measurements revealed a well-defined weak antilocalization effect below 10 K. Coherence lengths (Lø) as functions of temperature were derived from the magnetoresistance vs field curves by assuming the Hikami-Larkin-Nagaoka model. The anti-dot thin film with wBi and t smaller than λF showed low dimensional electronic behavior at low temperatures where Lø/(T) exceed wBi or t. [ABSTRACT FROM AUTHOR]

Abstract: We have performed magneto transport measurements on a multi-layer graphene device fabricated by conventional mechanical exfoliation. Suppression of weak localization (WL) as evidenced by the negative magnetoresistance (NMR) centered at zero field, and reproducible universal conductance fluctuations (UCFs) are observed. Interestingly, it is found that the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are longer than those determined from fitting the amplitudes of the UCFs to theory in the low temperature regime (T ≤ 8 K). In the high temperature regime (T > 8 K), the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory. Our new results therefore indicate a difference in the electron phase-breaking process between the two models of WL and UCFs in graphene. We speculate that the presence of the capping and bottom graphene layers, which leads the enhancement of disorder in-between, improves the localization condition for WL effect during carrier transportation in the low temperature regime. With increasing temperature, the localization condition for WL in multi-layer graphene becomes much weaker due to strong thermal damping. Therefore, the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory at high temperatures. [Copyright &y& Elsevier]

Abstract: Magnetoresistivity ( ) measurements of polycrystalline YBa2Cu3Oy (Y-123) and YBa2Cu3Oy embedded with nanoparticles of Y-deficient Y-123, generated by the planetary ball milling, have been compared and analyzed by the Ambegaokar and Halperin phase slip model (AH) and thermally activated flux creep (TAFC). Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDXS), were carried out. SEM analyses show that nanoparticles of Y-deficient Y-123, generated by ball milling, are embedded in the superconducting matrix. The broadening of the resistive transition under magnetic field is found to possess two distinct regions, which suggests that dissipation phenomenon in milled and unmilled samples is caused by two mechanisms: the order parameter fluctuations and the vortex-dynamics separated by a crossover temperature . The critical current at zero temperature in the grain boundaries decreases as a power law, , which is an indication of the sensitivity of a single junction between the superconducting grains to the applied magnetic field. of the milled material is higher than the one of the unmilled and the activation energies of vortex flux motion behavior in the applied magnetic field is enhanced by the presence of the nanoparticles embedded in the matrix. [Copyright &y& Elsevier]

We present local magnetoresistance measurements on carbon nanotubes contacted with the ferromagnetic alloy Co50 Pd50. A sample with contacts of [ABSTRACT FROM AUTHOR]

The electrical transport of the highly conductive poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is investigated with Ohmic and spin-polarized tunnel contacts at nanoscale lateral dimensions. Temperature-dependent charge transport measurements reveal that electrical conductivity scales non-linearly as a function of electrode spacing, which is attributed to the localization of carriers induced by the disorder introduced by the PSS polyelectrolyte. In addition, we demonstrate the integration of this conducting polymer in nanoscale lateral spin-valve devices by increasing the pH of the PEDOT:PSS solution. We present charge and magnetotransport measurement results of NiFe/AlOx/PEDOT:PSS/AlOx/NiFe lateral structures for various thicknesses of the alumina tunnel barriers. We discuss the absence of magnetoresistance of our spin valves within the framework of Valet–Fert theory, and estimate an upper limit for the spin lifetime of carriers in PEDOT:PSS to τsf ⩽ 50 ns. [ABSTRACT FROM AUTHOR]

We have investigated the origin of low-temperature resistivity minima observed in epitaxial thin films of LaCaMnO (thicknesses-300 Å and 3000 Å) using electrical and magneto-transport property measurements. We observe considerably smaller hysteresis in the magnetoresistance measurements for the thicker film than the thinner film. 300 Å film shows meta-stability in the resistivity measurements at low temperature and for this film the sample current ' I' shows large effect on the resistivity and its minima temperature. These observations suggest that the strain induces electronic intra grain inhomogeneity in these samples and these inhomogeneities consist of regions of different resistive phases. It appears that the high resistive phase prevents the transport of charge carriers between two low resistive regions thus giving rise to the resistivity minimum in these samples. [ABSTRACT FROM AUTHOR]

Structural and magnetic phase transitions of Mn-rich Mn50.5−xNi41Sn8.5+x (x = 0, 1 and 2) alloys were studied by magnetic and electrical measurements. The shift in martensitic transition temperature was less sensitive to the Mn/Sn ratio as compared to the Ni/Sn ratio. A magnetic entropy change (ΔSM) ∼ 11.85 J kg−1 K−1 was obtained for x = 0 at 270 K due to a change in magnetic field ΔH of only 1.5 T. Incorporating hysteresis losses, the net refrigerant capacity was estimated to be 44.82 J kg−1 for the same sample, which was found to be larger than that of other reported Ni-rich Ni–Mn–Sn alloys. Nearly 33% magnetoresistance was achieved for these alloys in presence of 8 T field differences. [ABSTRACT FROM AUTHOR]