Showing papers on "Magnetoresistance published in 2010"
TL;DR: In this paper, a 2DEG with an electron density as large as 8x10^13 cm^-2 was found at the bare SrTiO3 surface, and the electron density can be controlled through exposure of the surface to intense ultraviolet (UV) light.
Abstract: Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity, colossal magnetoresistance, or multiferroicity. The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO3 and SrTiO3 represents an important milestone towards exploiting such properties in all-oxide devices. This conducting interface shows a number of appealing properties, including a high electron mobility, superconductivity, and large magnetoresistance and can be patterned on the few-nanometer length scale. However, the microscopic origin of the interface 2DEG is poorly understood. Here, we show that a similar 2DEG, with an electron density as large as 8x10^13 cm^-2, can be formed at the bare SrTiO3 surface. Furthermore, we find that the 2DEG density can be controlled through exposure of the surface to intense ultraviolet (UV) light. Subsequent angle-resolved photoemission spectroscopy (ARPES) measurements reveal an unusual coexistence of a light quasiparticle mass and signatures of strong many-body interactions.
329 citations
TL;DR: In this paper, ultrathin Co/Pt]n and [Co/Pd]n superlattice films consisting of 0.14-0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering.
Abstract: Ultrathin [Co/Pt]n and [Co/Pd]n superlattice films consisting of 0.14–0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3–9)×106 ergs/cm3] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2–2.4 nm. The films were stable against annealing up to 370 °C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 Ω μm2) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory.
249 citations
TL;DR: The experimental observation of a significant enhancement in the conductance of a graphene nanoribbon field-effect transistor in a perpendicular magnetic field is reported, with a negative magnetoresistance of nearly 100% observed at low temperatures, with over 50% remaining at room temperature.
Abstract: Graphene has unique electronic properties, and graphene nanoribbons are of particular interest because they exhibit a conduction bandgap that arises due to size confinement and edge effects. Theoretical studies have suggested that graphene nanoribbons could have interesting magneto-electronic properties, with a very large predicted magnetoresistance. Here, we report the experimental observation of a significant enhancement in the conductance of a graphene nanoribbon field-effect transistor by a perpendicular magnetic field. A negative magnetoresistance of nearly 100% was observed at low temperatures, with over 50% magnetoresistance remaining at room temperature. This magnetoresistance can be tuned by varying the gate or source-drain bias. We also find that the charge transport in the nanoribbons is not significantly modified by an in-plane magnetic field. The large observed values of magnetoresistance may be attributed to the reduction of quantum confinement through the formation of cyclotron orbits and the delocalization effect under the perpendicular magnetic field.
249 citations
TL;DR: Analysis of the current-voltage characteristics indicates that the spin-dependent carrier injection correlates with the observed MR, and depositing nanodots instead of atoms onto the organic layer using buffer layer assist growth produces a sharper interface and a giant MR.
Abstract: Interfacial diffusion between magnetic electrodes and organic spacer layers is a serious problem in the organic spintronics which complicates attempts to understand the spin-dependent transport mechanism and hurts the achievement of a desirably high magnetoresistance (MR). We deposit nanodots instead of atoms onto the organic layer using buffer layer assist growth. Spin valves using this method exhibit a sharper interface and a giant MR of up to � 300%. Analysis of the current-voltage characteristics indicates that the spin-dependent carrier injection correlates with the observed MR.
233 citations
TL;DR: In this paper, a review of the progress achieved over the last one and a half decades on ED multilayer films with GMR effect and to critically evaluate the GMR results reported for various element combinations accessible to the electrodeposition (ED) technique for the preparation of FM/NM multi-layer films (ED multilayered nanowires will be treated very briefly only).
218 citations
TL;DR: In this paper, a two-step growth method was adopted for the van der Waals epitaxy of Bi2Se3 to proceed, and the in-plane growth rate anisotropy was exploited in order to achieve single crystalline Bi 2Se3 epifilms, in which threading defects and twins were effectively suppressed.
Abstract: The epitaxial growth of thin films of the topological insulator Bi2Se3 on nominally flat and vicinal Si(111) substrates was studied. In order to achieve a planar growth front and better quality epifilms, a two-step growth method was adopted for the van der Waals epitaxy of Bi2Se3 to proceed. By using vicinal Si(111) substrate surfaces, the in-plane growth rate anisotropy of Bi2Se3 was exploited in order to achieve single crystalline Bi2Se3 epifilms, in which threading defects and twins are effectively suppressed. The optimization of the growth parameters has resulted in the vicinal Bi2Se3 films showing a carrier mobility of ~2000 cm2 V−1 s−1 and a background doping of ~3×1018 cm−3 of the as-grown layers. Such samples not only show a relatively high magnetoresistance but also show a linear dependence on the magnetic field.
201 citations
Journal Article•
TL;DR: In this paper, the authors showed that the broken symmetry states arise from manybody interactions and underscore the important part that Coulomb interactions play in bilayer graphene, showing that the Coulomb interaction plays an important role in the broken-symmetry states.
Abstract: D 0 state, the devices show extremely high magnetoresistance that scales as magnetic field divided by temperature. This resistance is predominantly affected by the perpendicular component of the applied field, and the extracted energy gap is significantly larger than expected for Zeeman splitting. These findings indicate that the broken-symmetry states arise from manybody interactions and underscore the important part that Coulomb interactions play in bilayer graphene.
183 citations
TL;DR: In this paper, the first observation of linear magnetoresistance (LMR) in multilayer epitaxial graphene grown on SiC was reported and attributed to inhomogeneities in the epitaxially grown graphene film.
Abstract: We report the first observation of linear magnetoresistance (LMR) in multilayer epitaxial graphene grown on SiC. We show that multilayer epitaxial graphene exhibits large LMR from 2.2 K up to room temperature and that it can be best explained by a purely quantum mechanical model. We attribute the observation of LMR to inhomogeneities in the epitaxially grown graphene film. The large magnitude of the LMR suggests potential for novel applications in areas such as high-density data storage and magnetic sensors and actuators.
183 citations
TL;DR: The diffusion equations, which describe spin-charge coupled transport on the helical metal surface of a three-dimensional topological insulator, are derived and a new magnetoresistance effect is predicted, which manifests in a non-Ohmic correction to a voltage drop between a ferromagnetic spin-polarized electrode and a nonmagnetic electrode.
Abstract: We derive diffusion equations, which describe spin-charge coupled transport on the helical metal surface of a three-dimensional topological insulator. The main feature of these equations is a large magnitude of the spin-charge coupling, which leads to interesting and observable effects. In particular, we predict a new magnetoresistance effect, which manifests in a non-Ohmic correction to a voltage drop between a ferromagnetic spin-polarized electrode and a nonmagnetic electrode, placed on top of the helical metal. This correction is proportional to the cross product of the spin polarization of the ferromagnetic electrode and the charge current between the two electrodes. We also demonstrate tunability of this effect by applying a gate voltage, which makes it possible to operate the proposed device as a transistor.
181 citations
TL;DR: In this article, the authors observed angular-dependent magnetoresistance (MR) oscillations in a high-quality single crystal with the carrier density of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}$, which is a topological insulator with residual bulk carriers.
Abstract: We observed pronounced angular-dependent magnetoresistance (MR) oscillations in a high-quality ${\text{Bi}}_{2}{\text{Se}}_{3}$ single crystal with the carrier density of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }{\text{cm}}^{\ensuremath{-}3}$, which is a topological insulator with residual bulk carriers. We show that the observed angular-dependent oscillations can be well simulated by using the parameters obtained from the Shubnikov-de Haas oscillations, which clarifies that the oscillations are essentially due to the bulk Fermi surface. By completely elucidating the bulk oscillations, this result paves the way for distinguishing the two-dimensional surface state in angular-dependent MR studies in ${\text{Bi}}_{2}{\text{Se}}_{3}$ with much lower carrier density. Besides, the present result provides a compelling demonstration of how the Landau quantization of a closed three-dimensional Fermi surface can give rise to pronounced angular-dependent MR oscillations.
181 citations
TL;DR: In this article, the conductance across the interface depends sensitively on the directions of the magnetizations of the two ferromagnets, showing anomalous behaviors compared with the conventional spin valve.
Abstract: We investigate charge transport in two-dimensional ferromagnet/ferromagnet junction on a topological insulator. The conductance across the interface depends sensitively on the directions of the magnetizations of the two ferromagnets, showing anomalous behaviors compared with the conventional spin valve. This stems from the way how the wave functions connect between both sides. It is found that the conductance depends strongly on the in-plane direction of the magnetization. Moreover, in sharp contrast to the conventional magnetoresistance effect, the conductance at the parallel configuration can be much smaller than that at the antiparallel configuration.
HGST1
TL;DR: This sensor's performance relies predominantly on STO properties such as spectral linewidth and frequency dispersion with magnetic field, rather than signal amplitude as in conventional magnetoresistive sensors, and is shown in measured devices to achieve large signal to noise ratios.
Abstract: Magnetic field detection with extremely high spatial resolution is crucial to applications in magnetic storage, biosensing, and magnetic imaging. Here, we present the concept of using a spin torque oscillator (STO) to detect magnetic fields by measuring the frequency of the oscillator. This sensor's performance relies predominantly on STO properties such as spectral linewidth and frequency dispersion with magnetic field, rather than signal amplitude as in conventional magnetoresistive sensors, and is shown in measured devices to achieve large signal to noise ratios. Using macrospin simulations, we describe oscillator designs for maximizing performance, making spin torque oscillators an attractive candidate to replace more commonly used sensors in nanoscale magnetic field sensing and future magnetic recording applications.
TL;DR: In this article, the authors demonstrate the importance of coherent tunneling for large TMR with Heusler alloys with microfabricated epitaxial magnetic tunneling junctions.
Abstract: Spin-dependent coherent tunneling has been experimentally observed in high-quality sputtered-deposited ${\text{Co}}_{2}\text{FeAl}/\text{MgO}/\text{CoFe}$ epitaxial magnetic tunneling junctions (MTJs). Consequently, the microfabricated MTJs manifest a very large tunnel magnetoresistance (TMR) at room temperature and an unexpectedly TMR oscillation as a function of MgO barrier thickness. First-principles electronic band calculations confirm the pronounced coherent tunneling effect and are in good agreement with the experimental data. The present work demonstrates the importance of coherent tunneling for large TMR with Heusler alloys
Journal Article•
TL;DR: The results strongly support the contention that, in magnetic nanostructures, Faraday's law of induction must be generalized to account for forces of purely spin origin and a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages.
Abstract: The electromotive force (e.m.f.) predicted by Faraday’s law reflects the forces acting on the charge, –e, of an electron moving through a device or circuit, and is proportional to the time derivative of the magnetic field. This conventional e.m.f. is usually absent for stationary circuits and static magnetic fields. There are also forces that act on the spin of an electron; it has been recently predicted that, for circuits that are in part composed of ferromagnetic materials, there arises an e.m.f. of spin origin even for a static magnetic field. This e.m.f. can be attributed to a time-varying magnetization of the host material, such as the motion of magnetic domains in a static magnetic field, and reflects the conversion of magnetic to electrical energy. Here we show that such an e.m.f. can indeed be induced by a static magnetic field in magnetic tunnel junctions containing zinc-blende-structured MnAs quantum nanomagnets. The observed e.m.f. operates on a timescale of approximately 102–103 seconds and results from the conversion of the magnetic energy of the superparamagnetic MnAs nanomagnets into electrical energy when these magnets undergo magnetic quantum tunnelling. As a consequence, a huge magnetoresistance of up to 100,000 per cent is observed for certain bias voltages. Our results strongly support the contention that, in magnetic nanostructures, Faraday’s law of induction must be generalized to account for forces of purely spin origin. The huge magnetoresistance and e.m.f. may find potential applications in high sensitivity magnetic sensors, as well as in new active devices such as ‘spin batteries’.
TL;DR: In this article, experiments indicate that ionic displacements associated with the polarization reversal in the ferroelectric barrier affect the complex band structure at ferromagnetic-ferroelectric interfaces.
Abstract: Experimental results on entirely complex oxide ferromagnetic/ferroelectric/ ferromagnetic tunnel junctions are presented in which the tunneling magnetoresistance is modified by applying low electric field pulses to the junctions. The experiments indicate that ionic displacements associated with the polarization reversal in the ferroelectric barrier affect the complex band structure at ferromagnetic-ferroelectric interfaces. The results are discussed in the framework ofthe theoretically predicted magnetoelectric interface effect and may lead to novel multistate memory devices.
TL;DR: In this paper, the fabrication and spin dependent tunneling studies of magnetic tunnel junctions (MTJ) grown on flexible organic substrates were reported, and it was shown that after twisting and bending the MTJ on flexible substrates the TMR magnitude is maintained which indicates that spin-dependent tunneling properties are preserved.
Abstract: We report on the fabrication and spin dependent tunneling studies of magnetic tunnel junctions (MTJs) grown on flexible organic substrates. We observe comparable tunneling magnetoresistance (TMR) effects in standard Co/Al2O3/Co MTJs grown on either buffered polyester based organic substrates or silicon wafers. Moreover we show that after twisting and bending the MTJs on flexible substrates the TMR magnitude is maintained which indicates that spin dependent tunneling properties are preserved. This demonstrates that MTJs based spintronics devices are compatible with embodied flexible organic electronics.
TL;DR: In this paper, the magnetic properties of single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20−100 nm were investigated.
Abstract: We report measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20−100 nm. Temperature-dependent resistivity and thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation with an enhancement of the TEP for smaller diameter wires up to 110 μV/K at T = 300 K. We measure the magnetoresistance in magnetic fields both parallel and perpendicular to the nanowire [110] axis, where strong anisotropic positive magnetoresistance behavior was observed.
TL;DR: In this article, the authors estimated the current perpendicular to plane (CPP)-magnetoresistance (MR) performance target required for hard disk drives (HDDs) with areal density from 2 to 5 Tb/in2, considering spin transfer torque (STT) and thermal magnetic noise.
Abstract: We estimated the current perpendicular to plane (CPP)-magnetoresistance (MR) performance target required for hard disk drives (HDDs) with areal density from 2 to 5 Tb/in2 , considering spin transfer torque (STT) and thermal magnetic noise. It is found that the noise due to STT drastically affects the MR performance target for low resistance area (RA) film. Read elements with higher RA (around 0.1-0.3 ?·?m2 ) are preferable to control STT. In addition, thermal magnetic noise remained smaller than media magnetic noise for 2 Tb/in2 while it becomes comparable to media magnetic noise for 5 Tb/in2 , suggesting the necessity of a new method to control thermal magnetic noise.
TL;DR: By directly observing magnetic domain walls and flux distributions using cryogenic Lorentz microscopy and electron holography, it is demonstrated that an applied magnetic field assists nucleation and growth of an ordered ferromagnetic phase.
Abstract: Direct observations of domain walls and flux distributions in manganite have shed new light on the dynamics of the ferromagnetic phase in colossal magnetoresistance.
Patent•
04 Aug 2010
TL;DR: In this article, a method was proposed to align crystal c-axes in magnetic layers near two opposed junction wall faces of a magnetoresistive element so as to be almost perpendicular to the junction wall face.
Abstract: The present invention is directed to align crystal c-axes in magnetic layers near two opposed junction wall faces of a magnetoresistive element so as to be almost perpendicular to the junction wall faces. A magnetic sensor stack body has, on a substrate, a magnetoresistive element whose electric resistance fluctuates when a bias magnetic field is applied and, on sides of opposed junction wall faces of the magnetoresistive element, field regions including magnetic layers for applying the bias magnetic field to the element. The magnetoresistive element has at least a ferromagnetic stack on a part of an antiferromagnetic layer, and width of an uppermost face of the ferromagnetic stack along a direction in which the junction wall faces are opposed to each other is smaller than width of an uppermost face of the antiferromagnetic layer in the same direction.
TL;DR: The resistance of a network of nanoscale loops of La2−xSrxCuO4 oscillates as a function of the magnetic flux through the loops in a way that cannot be explained by the classic Little-Parks effect, but also rules out some theoretical predictions about these systems as discussed by the authors.
Abstract: The resistance of a network of nanoscale loops of La2−xSrxCuO4 oscillates as a function of the magnetic flux through the loops in a way that cannot be explained by the classic Little–Parks effect, but also rules out some theoretical predictions about these systems.
TL;DR: The interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields is explored by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs.
Abstract: Organic semiconductors offer a unique environment to probe the hyperfine coupling of electronic spins to a nuclear spin bath. We explore the interaction of spins in electron-hole pairs in the presence of inhomogeneous hyperfine fields by monitoring the modulation of the current through an organic light emitting diode under coherent spin-resonant excitation. At weak driving fields, only one of the two spins in the pair precesses. As the driving field exceeds the difference in local hyperfine field experienced by electron and hole, both spins precess, leading to pronounced spin beating in the transient Rabi flopping of the current. We use this effect to measure the magnitude and spatial variation in hyperfine field on the scale of single carrier pairs, as required for evaluating models of organic magnetoresistance, improving organic spintronics devices, and illuminating spin decoherence mechanisms.
TL;DR: In this paper, the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature was investigated, where the high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) was used as a nondestructive technique to analyze CoFeB-MgO-CoFeB magnetic tunnel junctions.
Abstract: This work reports on hard x-ray photoelectron spectroscopy (HAXPES) of CoFeB based tunnel junctions. Aim is to explain the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature. The high bulk sensitivity of HAXPES was used as a nondestructive technique to analyze CoFeB–MgO–CoFeB magnetic tunnel junctions. The investigated samples were processed at different annealing temperatures from 523 to 923 K. Hard x-ray core level spectroscopy reveals an enforced diffusion of boron from the CoFeB into the adjacent Ta layer with increasing annealing temperature. The dependence of the tunneling magnetoresistance on the annealing temperature is explained by the combined effects of an improved crystalline structure together with a change in the spin polarization at the Fermi energy caused by the removal of boron from the CoFeB layer and Ta diffusion at high annealing temperature.
TL;DR: In this paper, the authors investigated spin-dependent electron transport through a zigzag graphene nanoribbon sample with two ferromagnetic strips deposit on two sides of the graphene ribbon.
Abstract: We investigate spin-dependent electron transport through a zigzag graphene nanoribbon sample with two ferromagnetic strips deposit on two sides of the graphene ribbon. Our results show that, for the antiparallel configurations of ferromagnetic strips, the conductance exhibits zero conductance plateau when the Fermi energy locates around the Dirac point and the sample shows the properties of a semiconductor. But for the parallel configurations, the energy band spectrum is metallic and the conductance is always equal to or larger than ${e}^{2}/h$. Thus the huge giant magnetoresistance effect can be achieved by altering the configurations of the ferromagnetic strips. Moreover, we study the spin-dependent conductance for the parallel configuration. It is found that the device shows half-metal behavior, in which it acts as a conductor to carriers of one spin orientation but as an insulator to those of the opposite spin orientation. So the present device can be applied as a spin filter. In addition, we study the consequence of the short-range Anderson disorder and find that the spin filtering effect and magnetoresistance effect still remain even in the strong disorder limit.
TL;DR: Graphene extraordinary magnetoresistance (EMR) devices have been fabricated and characterized in varying magnetic fields at room temperature as discussed by the authors, and the device sensitivity can reach 10 mV/Oe, larger than state of the art 2DEG devices of comparable size and can be tuned by the electric field effect via a back gate or by imposing a biasing magnetic field.
Abstract: Graphene extraordinary magnetoresistance (EMR) devices have been fabricated and characterized in varying magnetic fields at room temperature. The atomic thickness, high carrier mobility and high current carrying capabilities of graphene are ideally suited for the detection of nanoscale sized magnetic domains. The device sensitivity can reach 10 mV/Oe, larger than state of the art InAs 2DEG devices of comparable size and can be tuned by the electric field effect via a back gate or by imposing a biasing magnetic field.
TL;DR: In this article, the authors fabricated perpendicularly magnetized MgO-based magnetic tunnel junctions with a [Co/Pt]n/CoFeB/TbFeCo bottom electrode layer (free layer) and a CoFe/Co FeB/TsFeCo top electrode layer(reference layer) with high magnetoresistance (MR) ratios of up to 85% at room temperature.
Abstract: We fabricated perpendicularly magnetized MgO-based magnetic tunnel junctions (p-MgO-MTJs) with a [Co/Pt]n/CoFeB/CoFe bottom electrode layer (free layer) and a CoFe/CoFeB/TbFeCo top electrode layer (reference layer). The insertion of thin CoFeB/CoFe layers at the barrier/electrode interfaces and post-annealing at a relatively low temperature of 225 °C simultaneously yielded high magnetoresistance (MR) ratios of up to 85% at room temperature and a low resistance–area (RA) product of 4.4 Ω µm2. Such a high MR ratio in low-RA p-MgO-MTJs is the key to developing ultrahigh-density spin-transfer-torque magnetoresistive random access memories (MRAMs).
TL;DR: In this paper, the spin-dependent screening potential of a multiferroic tunnel junction (MFTJ) was investigated and it was shown that spin-independent screening may provide significant contributions to TMR and TER in MFTJ.
Abstract: Using a ferroelectric barrier as a functional material in a (magnetic) tunnel junction has recently attracted significant interest due to new functionalities not available in conventional tunnel junctions. Switching a ferroelectric polarization of the barrier alters conductance resulting in a tunneling electroresistance (TER) effect. Using a ferroelectric barrier in a magnetic tunnel junction makes it mutiferroic where TER coexists with tunneling magnetoresistance (TMR). Here we develop a simple model for a multiferroic tunnel junction (MFTJ) which consists of two ferromagnetic electrodes separated by a ferroelectric barrier layer. The model explicitly includes the spin-dependent screening potential and thus extends previously developed models for FTJs and MFTJs. Our results demonstrate that the effect of spin-dependent screening may be sizable and may provide significant contributions to TMR and TER in MFTJs. We find that, similar to FTJs with a composite (ferroelectric/dielectric) barrier layer, the TER in a MFTJ with such a barrier is dramatically enhanced indicating that the resistance ratio between the states corresponding to the opposite polarization orientations may be as high as ${10}^{4}$ and even higher. Our results demonstrate the possibility of four resistance states in MFTJs with a pronounced difference in resistance and a possibility to control these resistance by an electric field (through ferroelectric polarization of the barrier) and by a magnetic field (through magnetization configuration of the electrodes). These functionalities may be interesting to device applications of MFTJs.
TL;DR: This work shows that multicomponent colloidal nanostructures can be used as the building blocks for design of multifunctional materials for electronics and optoelectronics.
Abstract: We report a synthesis of colloidal nanostructures combining a magnetic material (FePt) with a narrow-gap semiconductor (PbS and PbSe) in form of core−shells or nanodumbbells and explore their optical, magnetic, electrical, and magnetotransport properties. The arrays of “magnet-in-the-semiconductor” nanostructures show semiconductor-type transport properties with magnetoresistance typical for magnetic tunnel junctions, thus combining the advantages of both functional components. We observed gate-controlled charge transport through the arrays of FePt−PbS and FePt−PbSe core−shell nanostructures with an electron mobility of 0.01 cm2/(V s) and 0.08 cm2/(V s), respectively, combined with ferro- and superparamagnetic behavior and large tunneling magnetoresistance. This work shows that multicomponent colloidal nanostructures can be used as the building blocks for design of multifunctional materials for electronics and optoelectronics.
TL;DR: In this paper, the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field was studied by means of numerical calculations based on a tight-binding model. But the results for both clean (ballistic) and disordered (diffusive) rings are presented.
Abstract: We study the conductance of mesoscopic graphene rings in the presence of a perpendicular magnetic field by means of numerical calculations based on a tight-binding model. First, we consider the magnetoconductance of such rings and observe the Aharonov-Bohm effect. We investigate different regimes of the magnetic flux up to the quantum Hall regime, where the Aharonov-Bohm oscillations are suppressed. Results for both clean (ballistic) and disordered (diffusive) rings are presented. Second, we study rings with smooth mass boundary that are weakly coupled to leads. We show that the valley degeneracy of the eigenstates in closed graphene rings can be lifted by a small magnetic flux, and that this lifting can be observed in the transport properties of the system.
TL;DR: In this paper, a cubic phase and a trigonal phase with charge ordering state were identified at higher and lower temperatures, respectively, and the temperature dependence of the resistance indicates that the phase transition is a first-order transition.
Abstract: Polycrystalline PrCuMn6O12 sample has been successfully synthesized. It has been characterized by x-ray diffraction (XRD), magnetic and magnetotransport measurements at ambient pressure, and transport property measurements under pressures. From the refinements of XRD data, a cubic phase and a trigonal phase with charge ordering state were identified at higher and lower temperatures, respectively. The temperature dependence of the resistance indicates that the phase transition is a first-order transition. Both effective paramagnetic moments of the trigonal and cubic phases can be explained by orbital moment freezing theory. The transport property of the trigonal phase has been fitted with Mott's law for variable range hopping. Though the magnetoresistance value is not large, the pressure-induced resistance value change of PrCuMn6O12 is positive and achieves 264.8%. The cubic phase is suppressed under pressure and transformed to the trigonal phase at 15 kbar, indicating favor of the charge ordering state under pressure. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3294608]