Showing papers on "Magnetoresistance published in 1997"
TL;DR: In this paper, it was shown that the switching of resistive states in manganites can be achieved not only by a magnetic field, but also by an electric field for manganite oxides of the form Pr1−xCaxMnO3.
Abstract: Magnetoresistive devices (based on, for example, magnetic multilayers1) exhibit large changes in electrical resistance in response to a magnetic field, which has led to dramatic improvements in the data density and reading speed of magnetic recording systems Manganese oxides having a perovskite structure (the so-called manganites) can exhibit a magnetoresistive response that is many orders of magnitude larger than that found for other materials, and there is therefore hope that these compounds might similarly be exploited for recording applications2,3,4,5,6,7,8,9,10,11 Here we show that the switching of resistive states in the manganites can be achieved not only by a magnetic field, but also by an electric field For manganites of the form Pr1−xCaxMnO3, we find that an electrical current (and by implication a static electric field) triggers the collapse of the low-temperature, electrically insulating charge-ordered state to a metallic ferromagnetic state We suggest that such a phenomenon could be exploited to pattern conducting ferromagnetic domains within an insulating antiferromagnetic matrix, and so provide a route for fabricating micrometre- or nanometre-scale electromagnets
930 citations
TL;DR: In this article, a combination of volume thermal expansion (with and without an applied field), magnetic susceptibility and small-angle neutron scattering measurements was used to detect magnetic polarons above the ferromagnetic ordering temperature, Tc.
Abstract: Manganese perovskites based on the compound LaMnO3 are attracting considerable theoretical and technological interest by virtue of their unusual magnetic and electronic properties1–4. Most notable of these properties is the extremely large change in resistivity that accompanies the application of a magnetic field, an effect known as 'colossal' magnetoresistance. The origin of this effect has been attributed5–7 to the presence of magnetic polarons—charge carriers accompanied by a localized (and magnetically polarized) distortion of the surrounding crystal lattice8,9— but their existence and properties remains a matter of speculation. Here, using a combination of volume thermal expansion (with and without an applied field), magnetic susceptibility and small-angle neutron scattering measurements, we present evidence for the existence of magnetic polarons above the ferromagnetic ordering temperature, Tc. We detect the spontaneous formation of localized ∼12-A magnetic clusters above Tc which, on application of a magnetic field, grow in size but decrease in number. We argue that the response of these magnetic polarons to an applied magnetic field underlies the pronounced magnetoresistive properties in the compounds (La1–xAx)2/3Ca1/3MnO3 (where A is Y or Tb).
743 citations
TL;DR: Doped rare-earth manganates, which are usually associated with colossal magnetoresistive properties, have been used as the semiconductor channel material of a prototypical epitaxial field effect device.
Abstract: Ferroelectric field effect devices offer the possibility of nonvolatile active memory elements. Doped rare-earth manganates, which are usually associated with colossal magnetoresistive properties, have been used as the semiconductor channel material of a prototypical epitaxial field effect device. The carrier concentration of the semiconductor channel can be "tuned" by varying the manganate stochiometry. A device with La0.7Ca0.3MnO3 as the semiconductor and PbZr0.2Ti0.8O3 as the ferroelectric gate exhibited a modulation in channel conductance of at least a factor of 3 and a retention loss of 3 percent after 45 minutes without power.
576 citations
TL;DR: In this paper, the authors describe a novel class of magnetoresistive compounds, the silver chalcogenides, and show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response.
Abstract: Several materials have been identified over the past few years as promising candidates for the development of new generations of magnetoresistive devices. These range from artificially engineered magnetic multilayers' and granular alloys, in which the magnetic-field response of interfacial spins modulates electron transport to give rise to 'giant' magnetoresistance, to the manganite peravskites, in which metal-insulator transitions driven by a magnetic field give rise to a `colossal' magnetoresistive response (albeit at very high fields). Here we describe a hitherto unexplored class of magnetoresistive compounds, the silver chalcogenides. At high temperatures, the compounds Ag_2S, Ag_2Se and Ag_2Te are superionic conductors; below similar to 400 K, ion migration is effectively frozen and the compounds are non-magnetic semiconductors that exhibit no appreciable magnetoresistance. We show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response. At room temperature and in a magnetic field of similar to 55 kOe, Ag_(2+δ)Se and Ag_(2+δ)Te show resistance increases of up to 200%, which are comparable with the colossal-magnetoresistance materials. Moreover, the resistance of our most responsive samples exhibits an unusual linear dependence on magnetic field, indicating both a potentially useful response down to fields of practical importance and a peculiarly long length scale associated with the underlying mechanism.
572 citations
IBM1
TL;DR: A zero bias anomaly is observed at low temperatures in the current-voltage characteristics of ferromagnetic tunnel junctions; the drop in the junction resistance with increasing bias voltage is greater for antiparallel alignment of the magnetic moments of the magnet electrodes than for parallel alignment.
Abstract: A zero bias anomaly is observed at low temperatures in the current-voltage characteristics of ferromagnetic tunnel junctions; the drop in the junction resistance with increasing bias voltage is greater for antiparallel alignment of the magnetic moments of the magnetic electrodes than for parallel alignment. The resulting decrease in the magnetoresistance of the junction is accounted for by spin excitations localized at the interfaces between the magnetic electrodes and the tunnel barrier.
463 citations
TL;DR: The metal-insulator transition is attributed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at the Curie point TC as discussed by the authors.
Abstract: The metal-insulator transition is mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type is ascribed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at TC . Here JH is the on-site Hund’s-rule exchange coupling of an e g electron with s51/2 to the t 2g ion core with S 53/2. Above TC, the e g electrons are localized by the random spin-dependent potential and conduction is by variable-range hopping. Over the whole temperature range, the resistivity varies as ln( r/r ‘) 5@T0$12( M/ MS) 2 %/T# 1/4 , where M/ MS is the reduced magnetization. The temperature and field dependence of the resistivity deduced from the molecular-field theory of the magnetization reproduces the experimental data over a wide range of temperature and field. @S0163-1829~97!04513-X# Interest in mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type has revived 1 with the observations of large negative magnetoresistive effects, 2,3 especially in suitably annealed thin films. 4 The magnetoresistance is greatest in the vicinity of the Curie point TC of ferromagnetic compositions which exhibit ‘‘metallic’’ ~temperatureindependent! conduction at low temperatures and thermally activated conduction above TC . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180 °. 5 Their electronic properties are re
427 citations
TL;DR: In this paper, a simple self-aligned process was used to fabricate magnetic tunnel junctions down to submicron sizes using optical and electron-beam lithography, and the shape of the field response of the magnetoresistance was varied by adjusting the shape anisotropy of one junction electrode.
Abstract: We have used a simple self-aligned process to fabricate magnetic tunnel junctions down to submicron sizes Optical and electron-beam lithographies were used to cover a range of areas spanning five orders of magnitude The bottom magnetic electrodes (Co or permalloy) in our junctions were exchange biased by an antiferromagnetic layer (MnFe) The top electrodes were made of soft magnetic materials (Co or permalloy) We have consistently obtained large magnetoresistance ratios (15%–22%) at room temperature and in fields of a few tens of Oe The shape of the field response of the magnetoresistance was varied from smooth to highly hysteretic by adjusting the shape anisotropy of one junction electrode
410 citations
TL;DR: In this article, the effect of specific structural defects on the CMR behavior of the compound La0.7Ca0.3MnO3 was elucidated, and thin film devices were made to isolate the contribution of a single grain boundary that was introduced into an epitaxial film of the material.
Abstract: A number of different compounds, such as those derived from LaMnO3, have recently been shown to exhibit very large changes (up to 106%) in electrical resistance when a magnetic field is applied1–4—a phenomenon known as colossal magnetoresistance (CMR). But magnetic fields of several tesla are typically required to obtain such a large magnetoresistive effect, thus limiting the potential for applications. Nevertheless the complex and intimate link between magnetic structure, crystallographic structure and electrical resistivity in CMR materials, in addition to being of fundamental scientific interest, appears to provide some scope for engineering a more sensitive magnetoresistive response. Here we elucidate the effect of specific structural defects on the CMR behaviour of the compound La0.7Ca0.3MnO3. We have made thin film devices that isolate the contribution of a single grain boundary that was introduced into an epitaxial film of the material by growing it on a bicrystal substrate. These devices display sharp resistance switching in magnetic fields orders of magnitude less than those normally associated with CMR. These results both provide insight into the role of grain boundaries, and demonstrate the potential for developing sub-micrometre magnetic field sensors based on the CMR effect.
389 citations
01 Apr 1997
TL;DR: In this paper, the authors review the recent advances in patterned magnetic nanostructures, a fast-emerging field, including state-of-the-art technology for patterning of magnetic nano-structures as small as 10 nm, and a new paradigm for ultra-high-density magnetic storage based on patterned single-domain elements.
Abstract: Nanofabrication, offering unprecedented capabilities in the manipulation of material structures and properties, opens up new opportunities for engineering innovative magnetic materials and devices, developing ultra-high-density magnetic storage, and understanding micromagnetics. This paper reviews the recent advances in patterned magnetic nanostructures, a fast-emerging field, including (1) state-of-the-art technology for patterning of magnetic nanostructures as small as 10 nm; (2) engineering of unique magnetic properties (such as domain structures, domain switching, and magnetoresistance) by patterning and controlling the size, shape, spacing, orientation, and compositions of magnetic materials; (3) quantized magnetic disks-a new paradigm for ultra-high-density magnetic storage based on patterned single-domain elements that have demonstrated a storage density of 65 Gb/in/sup 2/ (nearly two orders of magnitude higher than that in current commercial magnetic disks) and a capability of 400 Gb/in/sup 2/; (4) novel magnetoresistance sensors based on unique properties of magnetic nanostructures; (5) other applications of nanoscale patterning in magnetics such as the quantification of magnetic force microscopy (MFM) and a new ultra-high-resolution MFM tip; and (6) sub-10-nm imprint lithography-a new low-cost, high-throughput technology for manufacturing magnetic nanostructures.
386 citations
TL;DR: In this article, the double exchange mechanism was applied to manganite perovskites to obtain the colossal magnetoresistance (CMR) effect in the vicinity of the transition temperature, where charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration.
Abstract: Manganese oxides with a perovskite structure1 exhibit a transition between a paramagnetic insulating phase and a ferromagnetic metal phase. Associated with this transition is an effect known as colossal magnetoresistance2–5 (CMR)—in the vicinity of the transition temperature, the materials exhibit a large change in resistance in response to an applied magnetic field. Such an effect, if optimized, might find potential application in magnetic devices. But the criteria for achieving (and hence optimizing) CMR are not clear, presenting a challenge for materials scientists. The accepted description of CMR in the manganite perovskites invokes the 'double-exchange' mechanism, whereby charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration (Mn3+ and Mn4+), and inhibited by the formation of charge-induced localized lattice distortions6,7. Here we report the existence of a large magnetoresistive effect in a class of materials—Cr-based chalcogenide spinels—that do not possess heterovalency, distortion-inducing ions, manganese, oxygen or a perovskite structure. The realization of CMR in compounds having a spinel structure should open up a vast range of materials for the further exploration and exploitation of this effect.
381 citations
TL;DR: In this article, it was shown that in one such compound, Pr0.7Ca0.3MnO3, a transition from the insulating antiferromagnetic state to the metallic ferromagnetic states can be driven by illumination with X-rays at low temperatures (<40 K).
Abstract: Manganese oxides of the general formula A1–xBxMnO3 (where A and B are trivalent and divalent cations, respectively) have recently attracted considerable attention by virtue of their unusual magnetic and electronic properties1–9. For example, in some of these materials magnetic fields can drive insulator-to-metal transitions where both the conductivity and magnetization change dramatically—an effect termed 'colossal magneto-resistance'1–3—raising hopes for application of these materials in the magnetic recording industry1–9. Here we show that in one such compound, Pr0.7Ca0.3MnO3, a transition from the insulating antiferromagnetic state to the metallic ferromagnetic state can be driven by illumination with X-rays at low temperatures (<40 K). This transition is accompanied by significant changes in the lattice structure, and can be reversed by thermal cycling. This effect, undoubtedly a manifestation of the strong electron–lattice interactions believed to be responsible for the magnetoresistive properties of these materials6–9, provides insights into the physical mechanisms of persistent photoconductivity, and may also find applications in X-ray detection and X-ray lithographic patterning of ferromagnetic nanostructures.
TL;DR: In this paper, the same Hamiltonian was used to explain magnetoresistance in structures with collinear magnetic alignments and the spin flip and non-flip scattering present in domain walls.
Abstract: Domain walls in ferromagnetic metals are known to be a source of resistance since the early experiments on iron whiskers. Recently it has been possible to identify this contribution from data on cobalt and nickel films which display stripe domains in which the current is driven normal to the domain walls. With the same Hamiltonian as used to explain giant magnetoresistance in structures with collinear magnetic alignments we have determined the spin flip, as well as nonflip, scattering present in domain walls. We calculate the resistivity in zero field, i.e., in the presence of striped domains, and at saturation to show the amount of magnetoresistance that is attributable to domain wall scattering.
TL;DR: The low-field magnetoresistance properties of polycrystalline La0.67Sr0.33MnO3 and La 0.67CaO33MnsO3 thin films with different grain sizes have been investigated and compared with epitaxial films as discussed by the authors.
Abstract: The low-field magnetoresistance (MR) properties of polycrystalline La0.67Sr0.33MnO3 and La0.67CaO33MnO3 thin films with different grain sizes have been investigated and compared with epitaxial films. MR as high as 15% has been observed in the polycrystalline films at a field of 1500 Oe at low temperatures, whereas the MR of the epitaxial films is less than 0.3% in the same field range. Based on the magnetization dependence of the MR, the current-voltage characteristics, and the temperature dependence of the resistivity, we attribute the low-field MR to spin-dependent scattering of polarized electrons at the grain boundaries which serve as pinning centers for the magnetic domain walls.
TL;DR: In this paper, the grain-size-dependent transport properties in granular perovskite have been investigated and a resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with the experimental results.
Abstract: The grain-size-dependent transport properties in the granular perovskite ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{MnO}}_{3}$ have been investigated. A giant magnetoresistance (GMR) effect, similar to that observed in granular transition metals, and a crystal intrinsic colossal magnetoresistance (CMR) have been simultaneously observed. With grain growth, the GMR effect gradually weakens and the intrinsic CMR effect becomes prominent in the present granular system. A resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with our experimental results.
TL;DR: In this paper, the appearance of giant negative magnetoresistance in this structural type is demonstrated, which may be related to a possible I.S. spin ordering of trivalent cobalt in pyramidal and octahedral coordinations.
Abstract: New “112” phases, LnBaCo2O5.4, with an ordered oxygen deficient perovskite structure, derived from the YBaFeCuO5-type were studied for Ln=Eu, Gd. The appearance of giant negative magnetoresistance in this structural type is demonstrated. Resistance ratio R0/R7 T reaches at least 10 at 10 K, i.e., is significantly larger than those observed in the other cobalt perovskites, such as La1−xSrxCoO3. These properties are linked to an original magnetic behavior of these materials that exhibit two types of transition—antiferromagnetic to ferromagnetic, and ferromagnetic to paramagnetic—as T increases. This magnetic behavior may be related to a possible I.S. and L.S. spin ordering of trivalent cobalt in pyramidal and octahedral coordinations, respectively.
TL;DR: In this article, the magnetoresistive properties of all-oxide tunnel spin valves were investigated and several tunnel barriers were used including PrBa2(CuGa)3O7, CeO2 and SrTiO3.
Abstract: We report on the magnetoresistive properties of all-oxide tunnel spin valves in which electrodes of mixed valence manganites (La0.7Sr0.3MnO3) are separated by a thin insulating layer. The structures were prepared by Pulsed Laser Deposition and several tunnel barriers were used including PrBa2(CuGa)3O7, CeO2 and SrTiO3. The latter gives the largest magnetoresistive effect where the trilayer's resistance is increased by a factor of 5.5 at 50 Gauss and 4.2 K. Analysis of the temperature variation of the barrier resistivity shows that the dramatic loss of the magnetoresistive effect above 150 K is due to a reduced oxygen content of the interface between La0.7Sr0.3MnO3 and SrTiO3. Solving this problem should lead to similar results at room temperature.
TL;DR: The theoretical and experimental studies of the giant magnetoresistance effect in metallic magnetic multilayers with measuring current perpendicular to the interface planes are reviewed in this article, where the effects of interface roughness, potential steps at the interfaces, and realistic band structures are addressed.
Abstract: The theoretical and experimental studies of the giant magnetoresistance effect in metallic magnetic multilayers with measuring current perpendicular to the interface planes are reviewed. Theoretical formalisms of electronic transport in the inhomogeneous electron gas are critically compared with emphasis on the perpendicular magnetoresistance in multilayers. The effects of interface roughness, potential steps at the interfaces, and realistic band structures are addressed. The experimental determination of the perpendicular resistance of metallic multilayers requires either low-resistance measurement techniques or microfabricated samples with enhanced resistances. The experimental methods known at present are discussed and, where possible, compared with each other.
TL;DR: In this article, the magnetoresistance (MR) exhibits a peak around the Verwey transition, and the MR values as high as 32% have been observed for a 6600-AA{}-thick film at 60 K under a 4-T field.
Abstract: The magnetotransport and magnetic properties of epitaxial ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ thin films grown on (001)-oriented MgO substrates by pulsed-laser deposition have been investigated. The magnetoresistance (MR) exhibits a peak around the Verwey transition ${(T}_{\ensuremath{
u}})$ as has also been reported previously for single crystals. Additionally, we have observed that the MR increases monotonically below 100 K with decreasing temperature. MR values as high as 32% have been observed for a 6600-\AA{}-thick film at 60 K under a 4-T field. The enhanced low-temperature MR is attributed to a magnetic-field-dependent activation energy for electron hopping transport.
TL;DR: Low-field tunneling magnetoresistance was observed in films of half-metallic CrO2 that were grown by high-pressure thermal decomposition of CrO3, indicating the potential of this simple method to directly control the interface barrier characteristics that determine the magnetotransport properties.
Abstract: Low-field tunneling magnetoresistance was observed in films of half-metallic CrO2 that were grown by high-pressure thermal decomposition of CrO3. High-temperature annealing treatments modified the intergrain barriers of the as-grown films through surface decomposition of CrO2 into insulating Cr2O3, which led to a threefold enhancement of the low-field magnetoresistance. This enhancement indicates the potential of this simple method to directly control the interface barrier characteristics that determine the magnetotransport properties.
TL;DR: In this paper, the influence of overlayer metal Al on the junction magnetoresistance (JMR) was investigated and the optimum thickness of Al was observed to lie in the range of 1.6 nm to achieve good JMR in FM-I-FM junctions.
Abstract: Al2O3 tunnel barriers I, formed by the oxidization of Al metal of various thicknesses between two ferromagnetic (FM) films were investigated to understand the influence of overlayer metal Al on the junction magnetoresistance (JMR). The optimum thickness of Al was observed to lie in the range of 1–1.6 nm to achieve good JMR in FM–I–FM junctions. Additionally, such junctions can be used to study the magnetic proximity effect in ferromagnet/normal metal bilayer systems.
TL;DR: The magnetic and magnetotransport properties of perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound.
Abstract: The magnetic and magnetotransport properties of the perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound. A metal-to-insulator transition and colossal magnetoresistance have been observed near its spin freezing temperature; besides, the insulator behavior has been found to reappear at lower temperature. The formation of ferromagnetic and antiferromagnetic clusters and the competition between them with the introduction of Fe3+ ions, which do not participate in the double-exchange process, have been suggested to explain the experimental results.
Patent•
18 Dec 1997TL;DR: In this paper, a low switching field magnetoresistive tunneling junction memory cell including a first exchange coupled structure having a pair of magnetoregressive layers and an exchange interaction layer sandwiched therebetween so as to pin the magnetic vectors of the pair of layers anti-parallel, and electrically insulating material sandwiched between the first and second exchange coupled structures to form a magnetoresistsistive tunnelling junction.
Abstract: A low switching field magnetoresistive tunneling junction memory cell including a first exchange coupled structure having a pair of magnetoresistive layers and an exchange interaction layer sandwiched therebetween so as to pin the magnetic vectors of the pair of layers anti-parallel, a second exchange coupled structure having a pair of magnetoresistive layers and an exchange interaction layer sandwiched therebetween so as to pin the magnetic vectors of the pair of layers anti-parallel, and electrically insulating material sandwiched between the first and second exchange coupled structures to form a magnetoresistive tunneling junction. Each of the first and second exchange coupled structures, and hence the memory cell, has no net magnetic moment.
TL;DR: In this article, the dependence of the magnetoresistance on the magnetization is investigated by means of a theoretical model that is developed taking explicitly into account the magnetic moment distribution and the spin-dependent electron-impurity scattering within magnetic grains and at the interface between the grains and the metallic matrix.
Abstract: In granular solids, the magnetoresistance is directly related to the macroscopic magnetization, but this relationship is extremelly complex due to the distribution of grain sizes and the intergranular magnetic interactions The dependence of the magnetoresistance on the magnetization is here investigated by means of a theoretical model that is developed taking explicitly into account the magnetic moment distribution and the spin-dependent electron-impurity scattering within magnetic grains and at the interface between the grains and the metallic matrix Using this model, one can explain large experimental deviations from the parabolic behavior of the magnetoresistance vs magnetization curves that are typically expected for equal noninteracting superparamagnetic grains The expressions for the magnetization and magnetoresistance, obtained for general distribution funtions, are tested considering a log-normal-type distribution function by fitting on data obtained from melt-spun Cu${}_{90}$Co${}_{10}$ ribbons after annealing by dc Joule heating The experimental data are well traced using just three parameters that determine the particle size distribution, the particle density, and the ratio of the scattering cross section at the boundaries of the grains to the scattering cross section within the grains
TL;DR: In this paper, a single electron transistor (SET) with a fixed gate voltage and a single spin-polarized electron was investigated, and it was shown that the magnetic valve effect is enhanced in the Coulomb blockade region, where the magnetoresistance (MR) ratio of the off-state of the SET is more than 40%, while that of the on-state is 40%.
Abstract: We report on magnetotransport properties of a ferromagnetic single electron transistor (SET) in which tunnel resistance R T changes about 36-38% by the magnetic valve effect We find that the magnetic valve effect is enhanced in the Coulomb blockade region: The magnetoresistance (MR) ratio of the off-state of the SET is more than 40%, while that of the on-state is 40% A mechanism of enhancement by the higher-order tunneling process is proposed Furthermore, we find a monotonic phase shift of the Coulomb oscillations induced by the magnetic field, which results in magneto-Coulomb oscillations with fixed gate voltage A simple explanation for this effect based on a magnetic-field-induced change in the Fermi energy of the spin-polarized electrons in an island electrode is given
TL;DR: In this paper, the magnetic and transport properties of a series of Ga 1−x Mn x As GaAs samples with different Mn concentrations (x = 0.015−0.071) were studied.
TL;DR: For a La 0.8Sr0.2MnO3 film with a grain boundary angle θ=36.8° a field independent component r0=4.1×10−6
Abstract: Epitaxial ferromagnetic manganite films have been sputtered on bicrystal substrates. Their magnetoresistance was measured as a function of magnetic field and temperature. The grain boundary magnetoresistance at low temperature is separated from the intrinsic magnetoresistance near the Curie temperature. The grain boundary magnetoresistance peaks at about 100 Oe and saturates at about 2 kOe. For a La0.8Sr0.2MnO3 film with a grain boundary angle θ=36.8° a field independent component r0=4.1×10−6 Ω cm2 was separated from a field-dependent component which has its maximum rH=2.3×10−6 Ω cm2 for H of order the coercive field.
TL;DR: In this article, a transfer-matrix treatment of the tunnel conductance and magnetoresistance for tunneling through ferromagnet/insulator (semiconductor) single junctions and double junctions subject to a dc bias is presented.
Abstract: Based on the two-band model, we present a transfer-matrix treatment of the tunnel conductance and magnetoresistance for tunneling through ferromagnet/insulator (semiconductor) single junctions and double junctions subject to a dc bias. Our results are qualitatively in agreement with the experimental measurements for the single junction. For the double junction, we find that there exists, spin-polarized resonant tunneling and giant tunnel magnetoresistance. The highest value of the magnetoresistance in a double junction can reach 90%. We anticipate that our results will stimulate some interest in experimental efforts in designing spin-polarized resonant-tunneling devices.
TL;DR: In this article, spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3 was reported.
Abstract: We report spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. Large (factor of 5) changes of magnetoresistance induced by a field of ∼200 Oe are observed at 4.2 K. Junction I–V characteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of 0.81 for the conduction electrons. Above 100 K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3 barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures.
TL;DR: In this paper, the authors present a comprehensive series of electrical transport (conductivity, magnetoresistance, and Hall effect), thermodynamic (specific heat, magnetic susceptibility, and magnetization), and optical (reflectivity) measurements in varying temperature ranges between 0.05 and 330 K on high-quality FeSi single crystals grown by vapor transport.
Abstract: We present a comprehensive series of electrical transport (conductivity, magnetoresistance, and Hall effect), thermodynamic (specific heat, magnetic susceptibility, and magnetization), and optical (reflectivity) measurements in varying temperature ranges between 0.05 and 330 K on high-quality FeSi single crystals grown by vapor transport. The entire set of data can consistently be described with the usual relations for a (compensated $n$ type) semiconductor if an unconventional band structure is assumed. Compared to the results of mean-field band-structure calculations, the height of the peaks in the total density of states around the energy gap is considerably enhanced, implying enhanced effective masses. Most likely correlation effects are the source of these features. At very low temperatures we encounter metallic behavior. A low concentration of correlated itinerant charge carriers coexists with interacting magnetic moments.