Showing papers on "Magnetoresistance published in 2004"
TL;DR: A model interface is examined between two insulating perovskite oxides—LaAlO3 and SrTiO3—in which the termination layer at the interface is controlled on an atomic scale, presenting a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.
Abstract: Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.
3,977 citations
TL;DR: A giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs is reported, indicating that coherency of wave functions is conserved across the tunnel barrier.
Abstract: The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs)1,2 is the key to developing magnetoresistive random-access-memory (MRAM), magnetic sensors and novel programmable logic devices3,4,5. Conventional MTJs with an amorphous aluminium oxide tunnel barrier, which have been extensively studied for device applications, exhibit a magnetoresistance ratio up to 70% at room temperature6. This low magnetoresistance seriously limits the feasibility of spintronics devices. Here, we report a giant MR ratio up to 180% at room temperature in single-crystal Fe/MgO/Fe MTJs. The origin of this enormous TMR effect is coherent spin-polarized tunnelling, where the symmetry of electron wave functions plays an important role. Moreover, we observed that their tunnel magnetoresistance oscillates as a function of tunnel barrier thickness, indicating that coherency of wave functions is conserved across the tunnel barrier. The coherent TMR effect is a key to making spintronic devices with novel quantum-mechanical functions, and to developing gigabit-scale MRAM.
2,956 citations
IBM1
TL;DR: Sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to ∼220% at room temperature and ∼300% at low temperatures, which will accelerate the development of new families of spintronic devices.
Abstract: Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.
2,931 citations
TL;DR: The injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure is reported, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.
Abstract: A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance and tunnelling magnetoresistance in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics--'spintronics'. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors, spin-valve devices with semiconducting spacers have not yet been demonstrated. pi-conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron-phonon coupling and large spin coherence. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.
1,298 citations
TL;DR: Kondo correlations persisted despite the presence of ferromagnetism, but the Kondo peak in the differential conductance was split by an amount that decreased as the moments in the two electrodes were turned from parallel to antiparallel alignment.
Abstract: We measured Kondo-assisted tunneling via C60 molecules in contact with ferromagnetic nickel electrodes Kondo correlations persisted despite the presence of ferromagnetism, but the Kondo peak in the differential conductance was split by an amount that decreased (even to zero) as the moments in the two electrodes were turned from parallel to antiparallel alignment The splitting is too large to be explained by a local magnetic field However, the voltage, temperature, and magnetic field dependence of the signals agree with predictions for an exchange splitting of the Kondo resonance The Kondo effect leads to negative values of magnetoresistance, with magnitudes much larger than the Julliere estimate
493 citations
TL;DR: A new class of spintronic devices in which aspin-valve-like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets is introduced.
Abstract: We introduce a new class of spintronic devices in which a spin-valve-like effect results from strong spin-orbit coupling in a single ferromagnetic layer rather than from injection and detection of a spin-polarized current by two coupled ferromagnets. The effect is observed in a normal-metal--insulator--ferromagnetic-semiconductor tunneling device. This behavior is caused by the interplay of the anisotropic density of states in (Ga,Mn)As with respect to the magnetization direction and the two-step magnetization reversal process in this material.
348 citations
TL;DR: In this paper, high quality MgO/Fe3O4 core−shell nanowires have been successfully synthesized by depositing an epitaxial shell of Fe 3O4 onto single crystal MgOs.
Abstract: High quality MgO/Fe3O4 core−shell nanowires have been successfully synthesized by depositing an epitaxial shell of Fe3O4 onto single crystal MgO nanowires. The material composition and stoichoimetric ratio have been carefully examined and confirmed with a variety of characterization techniques. These novel structures have rendered unique opportunities to investigate the transport behavior and spintronic property of Fe3O4 in its one-dimensional form. Room-temperature magnetoresistance of ∼1.2% was observed in the as-synthesized nanowires under a magnetic field of B = 1.8 T, which has been attributed to the tunneling of spin-polarized electrons across the anti-phase boundaries.
310 citations
TL;DR: In this article, a magneto-resistance (MR) ratio of 88% at T = 293 K was reported for epitaxial magnetic tunnel junctions (MTJ), the highest value yet reported.
Abstract: We fabricated fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions (MTJs) and observed a magneto-resistance (MR) ratio of 88% at T = 293 K (146% at T = 20 K), the highest value yet reported. The origin of the high MR ratio is not the diffusive tunneling of Julliere's model but the coherent spin-polarized tunneling in epitaxial MTJs, in which only the electrons with totally symmetric wave functions with respect to the barrier-normal axis can tunnel. The bias-voltage dependence of the MR was very small, resulting in a high output voltage of 380 mV. This high voltage will help overcome problems in the development of high-density magnetoresistive random-access-memory (MRAM).
287 citations
TL;DR: In this paper, a large room temperature magnetoresistance (MR) effect in polyfluorene sandwich devices in weak magnetic fields was found and the effect is related to the hole current in the devices.
Abstract: We report on the discovery of a large, room temperature magnetoresistance (MR) effect in polyfluorene sandwich devices in weak magnetic fields. We characterize this effect and discuss its dependence on field direction, voltage, temperature, film thickness, electrode materials, and (unintentional) impurity concentration. Negative MR is usually observed, but positive MR can also be achieved under high applied electric fields. The MR effect reaches up to 10% at fields of 10 mT at room temperature. The effect shows only a weak temperature dependence and is independent of the sign and direction of the magnetic field. We find that the effect is related to the hole current in the devices. To the best of our knowledge, the discovered effect is not adequately described by any of the MR mechanisms known to date.
277 citations
TL;DR: In this article, the authors have integrated Co2MnSi, as a representative of the full-Heusler compound family, as one magnetic electrode into magnetic tunnel junctions.
Abstract: As a consequence of the growing theoretical predictions of 100% spin-polarized half- and full-Heusler compounds over the past six years, Heusler alloys are among the most promising materials class for future magnetoelectronic and spintronic applications. We have integrated Co2MnSi, as a representative of the full-Heusler compound family, as one magnetic electrode into magnetic tunnel junctions. The preparation strategy has been chosen so as to sputter Co2MnSi at room temperature onto a V-buffer layer, which assists in (110) texture formation, and to deposit the Al-barrier layer directly thereafter. After plasma oxidizing the Al-barrier layer, subsequent annealing leads (1) to the texture formation and (2) to the appropriate atomic ordering within the Co2MnSi, and (3) homogenizes the AlOx barrier. It is shown that the magnetic switching of the ferromagnetic electrodes is well controlled from room temperature down to 10K. The resulting tunnel magnetoresistance-effect amplitude of the Co2MnSi containing magn...
270 citations
TL;DR: Electrical measurements of relatively small diameter (2–5 nm) individual CNTs in the presence of an axial magnetic field are reported to confirm quantitatively the predicted values for µorb, a large orbital magnetic moment that is thought to play a role in the magnetic susceptibility of C NTs and the magnetoresistance observed in large multiwalled CNTS.
Abstract: The remarkable transport properties of carbon nanotubes (CNTs) are determined by their unusual electronic structure1. The electronic states of a carbon nanotube form one-dimensional electron and hole sub-bands, which, in general, are separated by an energy gap2,3. States near the energy gap are predicted4,5 to have an orbital magnetic moment, µorb, that is much larger than the Bohr magneton (the magnetic moment of an electron due to its spin). This large moment is due to the motion of electrons around the circumference of the nanotube, and is thought to play a role in the magnetic susceptibility of CNTs6,7,8,9 and the magnetoresistance observed in large multiwalled CNTs10,11,12. But the coupling between magnetic field and the electronic states of individual nanotubes remains to be quantified experimentally. Here we report electrical measurements of relatively small diameter (2–5 nm) individual CNTs in the presence of an axial magnetic field. We observe field-induced energy shifts of electronic states and the associated changes in sub-band structure, which enable us to confirm quantitatively the predicted values for µorb.
TL;DR: It is shown here that it is productive to consider transition metal monosilicides as potential alternatives for spintronics, and the discovery that the bulk metallic magnets derived from doping the narrow-gap insulator FeSi with Co share the very high anomalous Hall conductance of (GaMn)As, while displaying Curie temperatures as high as 53 K.
Abstract: Magnetic semiconductors are attracting great interest because of their potential use for spintronics, a new technology that merges electronics with the manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently emerged as the most popular materials for this new technology, and although their Curie temperatures are rising towards room temperature, these materials can only be fabricated in thin-film form, are heavily defective, and are not obviously compatible with Si. We show here that it is productive to consider transition metal monosilicides as potential alternatives. In particular, we report the discovery that the bulk metallic magnets derived from doping the narrow-gap insulator FeSi with Co share the very high anomalous Hall conductance of (GaMn)As, while displaying Curie temperatures as high as 53 K. Our work opens up a new arena for spintronics, involving a bulk material based only on transition metals and Si, which displays large magnetic-field effects on its electrical properties.
TL;DR: In this paper, the authors reported ferromagnetism at over 900k in Cr-GaN and Cr-AlN thin films, and showed that substitutional Cr defects are involved in the magnetic behavior.
Abstract: We report ferromagnetism at over 900K in Cr–GaN and Cr–AlN thin films. The magnetic properties vary as a function of Cr concentration with 60%, and 20%, of the Cr being magnetically active at 3% doping in GaN, and 7% in AlN, respectively. In the GaN sample with the highest magnetically active Cr (60%), channeling Rutherford backscattering indicates that over 70% of Cr impurities are located on substitutional sites. These results give indisputable evidence that substitutional Cr defects are involved in the magnetic behavior. While Cr–AlN is highly resistive, Cr–GaN exhibits properties characteristic of hopping conduction including T−1∕2 resistivity dependence and small Hall mobility (0.06cm2∕Vs). A large negative magnetoresistance is attributed to the influence of the magnetic field on the quantum interference between the many paths linking two hopping sites. The results strongly suggest that ferromagnetism in Cr–GaN and Cr–AlN can be attributed to the double exchange mechanism as a result of hopping betwe...
TL;DR: In this article, the authors reported the observation of ferromagnetism at over 900k in Cr-GaN and Cr-AlN thin films, showing that 14% and 20% of the Cr atoms are magnetically active.
Abstract: We report the observation of ferromagnetism at over 900K in Cr-GaN and Cr-AlN thin films. The saturation magnetization moments in our best films of Cr-GaN and Cr-AlN at low temperatures are 0.42 and 0.6 u_B/Cr atom, respectively, indicating that 14% and 20%, of the Cr atoms, respectively, are magnetically active. While Cr-AlN is highly resistive, Cr-GaN exhibits thermally activated conduction that follows the exponential law expected for variable range hopping between localized states. Hall measurements on a Cr-GaN sample indicate a mobility of 0.06 cm^2/V.s, which falls in the range characteristic of hopping conduction, and a free carrier density (1.4E20/cm^3), which is similar in magnitude to the measured magnetically-active Cr concentration (4.9E19/cm^3). A large negative magnetoresistance is attributed to scattering from loose spins associated with non-ferromagnetic impurities. The results indicate that ferromagnetism in Cr-GaN and Cr-AlN can be attributed to the double exchange mechanism as a result of hopping between near-midgap substitutional Cr impurity bands.
TL;DR: In this article, the authors derived the quantum Boltzmann equation for the two-dimensional electron gas in a magnetic field such that the filling factor of the system can be characterized by Shubnikov-de Haas oscillations, smooth part of the magnetoresistance, and nonlinear transport.
Abstract: We derive the quantum Boltzmann equation for the two-dimensional electron gas in a magnetic field such that the filling factor $\ensuremath{
u}\ensuremath{\gg}1.$ This equation describes all of the effects of the external fields on the impurity collision integral including Shubnikov--de Haas oscillations, the smooth part of the magnetoresistance, and nonlinear transport. Furthermore, we obtain quantitative results for the effect of the external microwave radiation on the linear and nonlinear dc transport in the system. Our findings are relevant for the description of the oscillating resistivity discovered by Zudov et al., the zero-resistance state discovered by Mani et al. and Zudov et al., and for the microscopic justification of the model of Andreev et al. We also present a semiclassical picture for the qualitative consideration of the effects of the applied field on the collision integral.
TL;DR: Experimental evidence is provided for characteristic features of spin accumulation in magnetic nanoparticles, such as oscillations of the magnetoresistance with a periodical sign change as a function of bias voltage, in microfabricated devices containing cobalt nanoparticles.
Abstract: Spin injection and accumulation are key phenomena supporting a variety of concepts for spin-electronic devices. These phenomena are expected to be enhanced in nanoparticles over bulk structures due to their discrete energy levels and large charging energies. In this article, precise magnetotransport measurements in the single-electron tunnelling regime are performed by preparing appropriate microfabricated devices containing cobalt nanoparticles. Here we provide experimental evidence for characteristic features of spin accumulation in magnetic nanoparticles, such as oscillations of the magnetoresistance with a periodical sign change as a function of bias voltage. Theoretical analysis of the magnetoresistance behaviour clearly shows that the spin-relaxation time in nanoparticles is highly enhanced in comparison with that in the bulk.
TL;DR: The results confirm a f-independent 1/4-cycle phase shift with respect to the hf=j variant Planck's over 2pi omega(c) condition for j>/=1, and suggest a small reduction in the effective mass ratio, m(*)/m, withrespect to the standard value for GaAs/AlGaAs devices.
Abstract: We examine the phase and the period of the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices utilizing in situ magnetic field calibration by electron spin resonance of diphenyl-picryl-hydrazal. The results confirm a f-independent 1/4-cycle phase shift with respect to the hf=j variant Planck's over 2pi omega(c) condition for j>/=1, and they also suggest a small ( approximately 2%) reduction in the effective mass ratio, m(*)/m, with respect to the standard value for GaAs/AlGaAs devices.
TL;DR: Experimental transport results in 2D electron systems exposed to dipole radiation up to 20 GHz show Magnetoresistance oscillations occur as seen with higher frequency radiation; however, minima here can be seen to extend to negative biases, and zeros are not observed persistently around sample perimeters.
Abstract: We report experimental transport results in 2D electron systems exposed to dipole radiation up to 20 GHz. Magnetoresistance oscillations occur as seen with higher frequency radiation; however, minima here can be seen to extend to negative biases, and zeros are not observed persistently around sample perimeters. Under radiation, voltages are generated from internal to external contacts in the absence of applied driving currents. These findings may be consistent with theoretical pictures of current instabilities due to local negative resistivities.
TL;DR: In this paper, a multiwalled carbon nanotube polyaniline composite with cable-like morphology was synthesized by an in situ chemical oxidative polymerization directed with cationic surfactant cetyltrimethylammonium bromide.
Abstract: A multiwalled carbon nanotube∕polyaniline composite with cablelike morphology has been synthesized by an in situ chemical oxidative polymerization directed with cationic surfactant cetyltrimethylammonium bromide. It is interestingly found that with increasing carbon nanotube loading from 0 to 24.8wt%, the conductivity increases by two orders of magnitude and the Mott’s characteristic temperature T0 which depends on the hopping barrier decreases by three orders of magnitude. Furthermore, the low-temperature magnetoresistance has also changed the sign from positive to negative. The results reveal a strong coupling between the carbon nanotube and the tightly coated polymer chains, which enhances the average localization length and the electronic properties of the composites.
TL;DR: In this article, the magnitude of resistance is found to depend rather strongly on relative orientations of magnetization and current and their directions in respect to crystal axes, the configuration corresponding to the highest resistance being different for compressive and tensile strain.
Abstract: Hall and sheet resistance of 200-nm thick metallic (Ga,Mn)As with compressive and tensile strain has been measured as a function of the magnetic field and temperature. The magnitude of resistance is found to depend rather strongly on relative orientations of magnetization and current and their directions in respect to crystal axes, the configuration corresponding to the highest resistance being different for compressive and tensile strain. Negative magnetoresistance, which is observed even if magnetization becomes saturated, is assigned to weak localization.
TL;DR: The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe/MgO/Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe/ MgO interface.
Abstract: The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe/MgO/Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe/MgO interface. The voltage variation of the conductance points out the signature of an interfacial resonance state located in the minority band of Fe(001). When coupled to a metallic bulk state, this spin-polarized interfacial state enhances the band matching at the interface and therefore increases strongly the conductivity in the antiparallel magnetization configuration. Consequently, the tunnel magnetoresistance is found to be positive below 0.2 V and negative above. On the other hand, when the interfacial state is either destroyed by roughness-related disorder or not coupled to the bulk, the magnetoresistance is almost independent on the bias voltage.
TL;DR: Current-driven magnetization reversal in a ferromagnetic semiconductor based (Ga,Mn)As/ GaAs/GaAs/(Ga,Nm)As magnetic tunnel junction is demonstrated at 30 K.
Abstract: Current-driven magnetization reversal in a ferromagnetic semiconductor based (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K. Magnetoresistance measurements combined with current pulse application on a rectangular 1.5 x 0.3 microm2 device revealed that magnetization switching occurs at low critical current densities of 1.1-2.2 x 10(5) A/cm2 despite the presence of spin-orbit interaction in the p-type semiconductor system. Possible mechanisms responsible for the effect are discussed.
TL;DR: In this article, the magnetoresistance effect of Zn-Ni ferrites was investigated and it was found that the magnetoregressive effect increases as the Ni content increases in Zn1−xNixFe2O4 up to x=0.2 and then again decreases and finally becomes negligible for x=1.0.
Abstract: Spinel-type ferrites are widely used in practical applications. A fascinating property of Zn-Ni ferrites which reveals a direction for application is reported. A large negative magnetoresistance effect has been observed in ZnFe2O4 and Ni substituted Zn1−xNixFe2O4 ferrites of spinel structure. These materials are either ferrimagnetic or paramagnetic at room temperature and a spin (cluster) glass transition was found for some compositions at low temperatures. The magnetoresistance is either parabolic or linear with respect to applied field up to 9 T depending on the compositions and temperatures. It was found that the magnetoresistance effect increases as the Ni content increases in Zn1−xNixFe2O4 up to x=0.2 and then again decreases and finally become negligible for x=1.0, i.e., NiFe2O4. This magnetoresistance effect can be explained with the help of spin-dependent scattering and the Yafet-Kittel angle of the Ni-substituted Zn-Ni ferrites.
TL;DR: In this paper, the authors investigated the properties of tunneling magnetoresistance (TMR) of (Ga,Mn)As trilayer structures with a GaAs intermediary barrier layer.
Abstract: We have investigated the properties of tunneling magnetoresistance (TMR) of (Ga,Mn)As trilayer structures with a GaAs intermediary barrier layer. TMR ratio of 290% is observed at 0.39 K around zero applied bias voltage. The bias dependence of TMR ratio as well as the temperature-dependent anisotropic behavior are presented.
TL;DR: In this article, the zero-field spin splitting and the effective magnetic field seen in the reference frame of the electron are evaluated from a quantitative study of beats observed in radiation-induced magneto-resistance oscillations.
Abstract: We suggest an approach for characterizing the zero-field spin splitting of high mobility two-dimensional electron systems, when beats are not readily observable in the Shubnikov-de Haas effect. The zero-field spin splitting and the effective magnetic field seen in the reference frame of the electron are evaluated from a quantitative study of beats observed in radiation-induced magneto-resistance oscillations.
TL;DR: In this paper, high-temperature ferromagnetism is demonstrated in Mn-doped indium-tin oxide (ITO) films deposited using reactive thermal evaporation.
Abstract: High-temperature ferromagnetism is demonstrated in Mn-doped indium–tin oxide (ITO) films deposited using reactive thermal evaporation. These films were grown on sapphire (0001), Si∕SiO2 as well as Si (100) substrates with the highest magnetic moment observed around 0.8μB∕Mn in 5% Mn-doped ITO films. The electrical conduction is n type and the carrier concentration is ∼2.5×1019cm−3 for 5% Mn doping. An anomalous Hall effect is observed in magnetotransport measurements, showing that the charge carriers are spin polarized, revealing the magnetic interaction between itinerant electrons and localized Mn spins. The carrier concentration can be varied independent of the Mn concentration in this transparent ferromagnetic semiconductor for its easy integration into magneto-optoelectronic devices.
TL;DR: In this article, a thin Co/Cu/permalloy (Ni80Fe20) pseudospin-valve structure is sandwiched between superconducting Nb contacts and when the current is passed perpendicular to the plane of the film a Josephson critical current (IC) is observed at 4.2 K, in addition to a magnetoresistance of ∼ 0.5% at high bias.
Abstract: A thin Co/Cu/permalloy (Ni80Fe20) pseudospin-valve structure is sandwiched between superconducting Nb contacts. When the current is passed perpendicular to the plane of the film a Josephson critical current (IC) is observed at 4.2 K, in addition to a magnetoresistance (MR) of ∼0.5% at high bias. The hysteresis loop of the spin-valve structure can be cycled to modulate the zero field IC of the junction in line with the MR measurements. These modulations of resistance and IC occur both smoothly and sharply with the field applied. For each type of behavior there is a strong correlation between the shape of the MR loops and the IC modulation.
TL;DR: In this article, the authors measured negative magnetoresistance (MR) in the ferromagnetic state for different compositions (x = 0-0.2), in the austenitic, pre-martensitic and martensitic phases.
Abstract: 5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni_{2+x}Mn_{1-x}Ga. This indicates the possibility of using Ni_{2+x}Mn_{1-x}Ga as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0-0.2) in the austenitic, pre-martensitic and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and pre-martensitic phases, in the martensitic phase it shows a cusp-like shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model.
TL;DR: Magnetic field effects (MFEs) in the luminescence and photoconductivity of organic crystals such as anthracene have been known since the 1960s as discussed by the authors, while engaged in a project to use spin polarized current to manipulate electroluminescence (EL) in organic light emitting diodes based on a bilayer of tris(8-hydroxyquinoline) aluminum (Alq3) and N,N′-Di(naphthalen-1-yl)-N,N´diphenyl-benzidine (NPB
Abstract: Magnetic field effects (MFEs) in the luminescence and photoconductivity of organic crystals such as anthracene have been known since the 1960s. While engaged in a project to use spin polarized current to manipulate electroluminescence (EL) in organic light emitting diodes based on a bilayer of tris(8-hydroxyquinoline) aluminum (Alq3) and N,N′-Di(naphthalen-1-yl)-N,N′diphenyl-benzidine (NPB), we observed MFE similar to those reported in anthracene. The MFE consist of an increase in EL with increasing magnetic field of a few percent for small magnetic fields, a decrease in EL of greater than 20% at high fields and an increase in conductivity, i.e., negative magnetoresistance (MR), for all magnetic fields. The high field effect (HFE) is enhanced at lower temperatures and higher current densities and is similar to that reported for delayed luminescence in anthracene single crystals suggesting that triplet–triplet annihilation (TTA) influences light emission in Alq3. Transient EL studies were performed in an a...
TL;DR: An oxide bilayer junction has been fabricated by growing a La0.32Pr0.35Ca0.33MnO3 film on 0.5 wt % Nb-doped SrTiO3 crystal as discussed by the authors.
Abstract: An oxide bilayer junction has been fabricated by growing a La0.32Pr0.35Ca0.33MnO3 film on 0.5 wt % Nb-doped SrTiO3 crystal, and its behavior under magnetic field is experimentally studied. It is found that external field greatly affected the rectifying property and the resistance of the junction, causing an extremely large magnetoresistance. The most striking observation of the present work is that the magnetoresistance of the junction can be either positive or negative, depending on temperature and applied current, and is asymmetric with respect to the direction of the bias current. These results reveal the great potential of the manganites in configuring artificial devices.