Showing papers on "Colossal magnetoresistance published in 1994"
TL;DR: A negative isotropic magnetoresistance effect has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx, which could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized.
Abstract: A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.
4,079 citations
TL;DR: In this paper, a comprehensive review of giant magnetoresistance in spin-valve sandwiches and multilayers is presented, highlighting the experimental and theoretical results which are of particular interest for the development of applications of these systems, especially in magnetic recording technology.
451 citations
TL;DR: In this article, it was shown that the peak magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films.
Abstract: Colossal magnetoresistance with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. This magnetoresistance value is about three orders of magnitude higher than is typically seen in the giant‐magnetoresistance‐type metallic, superlattice films. The temperature of peak magnetoresistance is located in the region of metallic resistivity behavior. As the magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin‐disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films. The peak can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be very detrimental to achieving large magnetoresistance in the lanthanum manganite compounds. The fact th...
358 citations
TL;DR: In this paper, a colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La•Ca•Mn•O thin films.
Abstract: A colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. The effect is negative and isotropic with respect to the field orientations. The magnetoresistance is strongly temperature dependent, and exhibits a sharp peak that can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be detrimental to achieving very large magnetoresistance in the lanthanum manganite films. The orders of magnitude change in electrical resistivity could be useful for various magnetic and electric device applications.
326 citations
TL;DR: Both the variation of the magnetoresistance with magnetization in the film and the difference in the Magnetoresistance between the zero-field-cooled and field-cycled state are interpreted by invoking interactions between the active magnetic regions in the sample.
Abstract: We have observed magnetic and electrical transport properties in giant magnetoresistive inhomogeneous cobalt-silver films. The material consists of two distinct magnetic phases: large clusters which dominate the magnetization and magnetoresistive processes at room temperature, between which cooperative behavior is observed; and small clusters which dominate the magnetization below 10
obreak\ K, but make only a minor contribution to the magnetoresistance. Both the variation of the magnetoresistance with magnetization in the film and the difference in the magnetoresistance between the zero-field-cooled and field-cycled state are interpreted by invoking interactions between the active magnetic regions in the sample.
59 citations
TL;DR: In this article, structural, magnetic and electrotransport properties of as-deposited and annealed (Ni 80 Fe 20 ) χ Ag( 1−χ ) heterogeneous alloys prepared by sputtering are investigated.
51 citations
TL;DR: In this paper, the results of resistance and magnetoresistance measurements carried out during film growth were discussed, and the electronic transport parameters of these films and the growth mechanism of the layers were characterized.
Abstract: The transport properties of electrons in Co/Cu multilayered thin films are of special interest for the giant magnetoresistance (GMR) of this system. The magnitude of this effect depends on the mean free paths and on the strength of the interface scattering which in turn are strongly related to film structure. In this article, we discuss the results of resistance and magnetoresistance measurements carried out during film growth. We characterize the electronic transport parameters of these films and the growth mechanism of the layers. The new technique of the in situ measurement of the magnetoresistance furthermore provides a tool to find correlations of the growth mechanism with the dependence of the GMR on the Co thickness.
44 citations
TL;DR: In this article, the authors attributed the appearance of giant magnetoresistance to a magnetostatic interlayer interaction that promotes antiparallel order of the moments in adjacent layers fostered by a breakup of the NiFe layers.
Abstract: Giant magnetoresistance of order 4%–6% has been observed in fields of 5–10 Oe at room temperature in annealed multilayers of Ni80Fe20/Ag prepared by magnetron sputtering. For a wide range of NiFe and Ag thicknesses, no giant magnetoresistance was observed in the unannealed films. We attribute the appearance of giant magnetoresistance to a magnetostatic interlayer interaction that promotes antiparallel order of the moments in adjacent layers fostered by a breakup of the NiFe layers. We discuss the effects of variations in the underlayers, spacer thickness, and the sputtering process on the magnetoresistance. Our results suggest that maximizing magnetoresistance and minimizing hysteresis require samples with continuous Ag layers that prevent contact between the NiFe layers and NiFe layers that are discontinuous but not too severly disrupted.
44 citations
TL;DR: A linear dependence is found between the actual measured magnetoresistance and the fraction of AF coupling, as determined by magnetization measurements, which reveals evidence for strong spin-dependent interface scattering, whereas the spin dependence of the bulk scattering in Co is small.
Abstract: We have measured the magnetoresistance of high-vacuum-sputtered Co/Cu(100) multilayers grown on Cu buffer layers. The magnetoresistance in the first antiferromagnetic- (AF-) coupling peak is very sensitive to the buffer layer thickness. We find a linear dependence between the actual measured magnetoresistance and the fraction of AF coupling, as determined by magnetization measurements. We compare our Co/Cu(100) magnetoresistance data at 4 K of completely antiparallel-aligned multilayers with the quantum model of giant magnetoresistance of Levy, Zhang, and Fert. This reveals evidence for strong spin-dependent interface scattering, whereas the spin dependence of the bulk scattering in Co is small.
42 citations
TL;DR: It is shown by using the microscopic theory that the magnetoresistance increases with decreasing the size of magnetic grains, in agreement with experiment.
Abstract: Numerical simulation on resistance and giant magnetoresistance in magnetic granular alloys is performed for finite-size systems by making use of the real-space Green's-function method based on the Kubo formalism. Spin-dependent scattering causes the giant magnetoresistance in the magnetic granular alloys as in the magnetic multilayers. It is shown by using the microscopic theory that the magnetoresistance increases with decreasing the size of magnetic grains, in agreement with experiment. The theoretical results indicate that scattering at the surfaces of magnetic grains governs the resistance and magnetoresistance in granular alloys. Difference between the giant magnetoresistances in the granular alloys and multilayers is discussed.
41 citations
TL;DR: In this article, the authors observed large negative magnetoresistance (MR) in Cr•Fe heterogeneous alloy films sputter deposited on heated substrates and the largest MR, 37.3% at 4.2 K and 14 T, appears around the Fe concentration of 20 at.
Abstract: We have observed large negative magnetoresistance (MR) in Cr‐Fe heterogeneous alloy films sputter deposited on heated substrates. The largest MR, 37.3% at 4.2 K and 14 T, appears around the Fe concentration of 20 at. %. While a large substrate temperature dependence of MR is observed when the Fe concentration is lower than 20 at. %, MR does not vary noticeably with changes in the substrate temperature when Fe concentration exceeds 20 at. %.
TL;DR: In this article, the origin of the giant magnetoresistance of magnetic multilayers and magnetic granular solids is investigated through a unified spin-dependent linear transport theory, in which the primary source of electrical resistivity is short-range scattering by impurities in the different magnetic or nonmagnetic regions and at the interfaces.
Abstract: The origin of the giant magnetoresistance of magnetic multilayers and magnetic granular solids is investigated through a unified spin‐dependent linear transport theory, in which the primary source of electrical resistivity is short‐range scattering by impurities in the different magnetic or nonmagnetic regions and at the interfaces. Our theory predicts that magnetotransport in granular solids is similar to that for currents perpendicular to the plane of the layers in multilayers in that their magnetoresistance is independent of the average distance between adjacent magnetic regions.
TL;DR: In this paper, the results of measurements of the field and temperature dependences of the magnetoresistance of manganese ferrite and several other spinel ferrites are presented in a systematic manner and analyzed.
Abstract: The results of measurements of the field and temperature dependences of the magnetoresistance of manganese ferrite and several other spinel ferrites are presented in a systematic manner and analysed. In magnetic fields in excess of the technical saturation and at temperatures below the Curie point these ferrites have two physically different components of the isotropic negative magnetoresistance. One of them is due to the scattering of conduction ('hopping') electrons on paraprocess-induced variations of the order of the magnetic cations. The second component is interpreted on the basis of a 'magnetoelectron sublattice' model proposed by the author. Manifestations of the magnetoresistance in the vicinity of various phase transitions in spinel ferrites are considered.
TL;DR: In this paper, a very thin Ni80Fe20 film of 200 A exhibited a high magnetoresistance of 3.5% after an appropriate post-annealing treatment and the improvement is due to the decrease of zero-field resistivity resulting from remarkable grain growth in the films.
Abstract: We prepared Ni80Fe20 films by the sputter-beam method and investigated their magnetotransport properties. The very thin film of 200 A exhibited a high magnetoresistance of 3.5% after an appropriate post-annealing treatment. The improvement is due to the decrease of zero-field resistivity resulting from remarkable grain growth in the films. Taking into account diffusive electron scattering at the film surface, the magnetoresistance value is thought to be very close to that of the bulk.
01 Jan 1994
TL;DR: In this paper, Parkin et al. survey both theoretical and experimental aspects of coupling and magnetoresistivity in magnetic multilayers and conclude with a comparison of MBE-grown and sputtered films.
Abstract: In this chapter, the related subjects of magnetic coupling and magnetoresistance in ultrathin film structures are discussed in detail. Antiferromagnetic exchange coupling can occur between two ultrathin ferromagnetic films (e.g., Fe) separated by a non-magnetic spacer layer (e.g., Cr) of the correct thickness. Antiparallel alignment of the adjacent ferromagnetic layer magnetizations in Fe/Cr multilayers gives rise to the phenomenon of giant magnetoresistance via the so-called spin valve effect, although indirect exchange coupling is only one of several ways in which such an antiparallel alignment, and hence giant magnetoresistance, can be obtained. Oscillatory coupling has been found to occur in which the coupling strength oscillates as a function of thickness of the spacer layer, and in appropriate ferromagnetic/non-magnetic multilayer systems, this is accompanied by an oscillatory magnetoresistivity. In this chapter we survey both theoretical and experimental aspects of coupling and magnetoresistivity in magnetic multilayers. In the first section, a range of theoretical models proposed to explain exchange coupling are discussed by Hathaway. This is followed by a review by Fert and Bruno of the experimental results and theoretical models for interlayer coupling and magnetoresistance. Pierce, Unguris and Celotta discuss studies of exchange coupling using scanning electron microscopy with polarization analysis. This study focuses chiefly on epitaxial films. The reader is referred to Volume 1, Chap. 4 for a discussion of spin-polarized electron spectroscopy techniques. Finally, Parkin concludes the chapter with a discussion of giant magnetoresistance and coupling in polycrystalline transition metal multilayers. The reader is referred to this final section for a comparison of MBE-grown and sputtered films.
TL;DR: Au-Co and Au-Co-B alloys have been prepared by rapid solidification, followed by heat treatment as mentioned in this paper, and the magnetoresistance effect was less than 1% in the as-quenched samples and increased to about 3% after an appropriate heat treatment.
Abstract: Au‐Co and Au‐Co‐B alloys have been prepared by rapid solidification, followed by heat treatment. The precipitation of the ferromagnetic phases Co and Co2B in the Au matrix phase has been observed during annealing. At room temperature, both magnetization and magnetoresistance are determined by the superparamagnetic behavior of the ferromagnetic particles. The magnetoresistance is believed to have the same origin as that in multilayers and granular films. Both Co particles and the precipitates of the Co2B intermetallic phase give rise to a high magnetoresistance. The magnetoresistance effect was less than 1% in the as‐quenched samples and increased to about 3% after an appropriate heat treatment.
TL;DR: In this paper, the magnetoresistance along the c-axis of a single crystal of Bi 2 Sr 2 CaCu 2 O x (B i(2212)) was measured in pulsed high magnetic fields up to 40 T.
Abstract: The magnetoresistance along the c -axis of a single crystal of Bi 2 Sr 2 CaCu 2 O x ( B i(2212)) was measured in pulsed high magnetic fields up to 40 T. The resistance increased steeply from zero with the application of a magnetic field below T c ( B = 0), and became larger than the value just above T c , as was reported previously. In the high field region, however, decrease of the resistance was observed. It is shown that this experimental fact, a kind of negative magnetoresistance in the high field region, can be explained by the contribution of the density of states term to the fluctuation conductivity.
TL;DR: In this paper, the authors have fabricated pillar-like microstructures of Fe/Cr and Co/Cu magnetic multilayers and measured the giant magnetoresistance effect with the current perpendicular to the multilayer plane.
Abstract: We have fabricated pillar-like microstructures of Fe/Cr and Co/Cu magnetic multilayers and measured the giant magnetoresistance effect with the current perpendicular to the multilayer plane. The perpendicular giant magnetoresistance effect was determined as a function of temperature from 4 K to 300 K. For both Fe/Cr and Co/Cu multilayers we find, at low temperature, magnetoresistance effects of the order of 100%. The Fe/Cr pillars show a pronounced decrease with temperature of the magnetoresistance, while for Co/Cu the temperature dependence is much weaker. This different behaviour is caused by the different temperature dependence of the spin-dependent scattering; in the case of Co/Cu, we present results of a quantitative analysis of the temperature dependence using a resistance model of Fert and Campbell, originally proposed for magnetic alloys [1].
TL;DR: In this paper, the consequences of spin-dependent scattering for the giant magnetoresistance (GMR) effect in uranium intermetallics are discussed and compared with the behavior in multilayer systems.
Abstract: The enormous magnetoresistance effect at low temperatures in various uranium‐based intermetallic compounds, which exceeds by far the effect found in magnetic‐multilayer systems, is a consequence of the strong 5f conduction electron hybridization The consequences of spin‐dependent scattering for the giant magnetoresistance (GMR) effect in uranium intermetallics will be discussed and compared with the behavior in multilayer systems Possible changes of the model parameters to achieve giant magnetoresistance (GMR) effects at higher temperatures, which are desirable for practical applications, are considered
TL;DR: Magnetoresistance of a strongly correlated material, La1−xCaxMnOz film was investigated in this paper, where films were fabricated on MgO(100) single crystal substrates by an ion beams sputtering method.
Abstract: Magnetoresistance of a strongly correlated material, La1−xCaxMnOz film was investigated. Films were fabricated on MgO(100) single crystal substrates by an ion beams sputtering method. A giant and isotropic magnetoresistance effect was observed for which the maximum was as huge as −53 %. The maximum value was obtained at the critical temperature of the M-I (metal-insulator) transition. By consideration of the spin dynamics together with temperature dependency of magnetoresistance, the magnetoresistance effect was attributed to spin-dependent electron scattering due to fluctuation of the spin canting angle.
TL;DR: In this paper, a mechanism leading to anomalous magnetoresistance in composite metallic conductors is investigated, including a high purity aluminum conductor with a low purity core, which is an extension of previous work.
Abstract: A mechanism leading to anomalous magnetoresistance in composite metallic conductors is investigated. Both steady state and transient phenomena are studied. This work includes analysis of a high purity aluminum conductor with a low purity core, which is an extension of previous work.
TL;DR: In this article, a summary of detailed measurements of the longitudinal and transverse magnetoresistance of ternary Pd1−xFex)95Mn5 samples is presented.
Abstract: A summary of detailed measurements of the longitudinal and transverse magnetoresistance, and of the anisotropy in the magnetoresistance of ternary (Pd1−xFex)95Mn5 samples, is presented. While neither the longitudinal nor the transverse magnetoresistance saturate, these data suggest that the anisotropy (i.e., the difference) might become field independent in quite moderate fields. This feature enables a comparison to be made between this ternary system and binary PdFe, as a function of composition and temperature
TL;DR: In this paper, the anisotropic magnetoresistance (AMR) in both the high resistance and low resistance GMR states was measured with the Co magnetizations aligned parallel to one another (the low resistance MGR state) and with the magnetization aligned antiparallel to oneAnother (the high resistance GMM state).
Abstract: By a systematic variation of structures, recent measurements conclude the scattering associated with the high resistance giant magnetoresistance (GMR) state occurs within 0.25 nm of the magnetic interface. We have accomplished a similar measurement that does not require such stringent control of the sample structure. Instead, the present work uses measurements of the anisotropic magnetoresistance (AMR) in both the high resistance and low resistance GMR states. The samples are sandwiches of Co/Cu/Co/CoO with Co thicknesses ranging from 1 to 10 nm and Cu thickness of approximately 2.5 nm. The AMR is measured with the Co magnetizations aligned parallel to one another (the low resistance GMR state) and with the Co magnetizations aligned antiparallel to one another (the high resistance GMR state). The data show that the AMR in the antiparallel configuration is less than that in the parallel configuration. An analysis that relates the reduced AMR to the magnetic interfacial region giving rise to the high resist...
TL;DR: Magnetoresistance measurements have been performed on epitaxial metal/ferromagnetic insulator bilayers as mentioned in this paper, showing that the conduction electrons of the metal are coupled to the spins in the magnetic insulator, and act as probes of the magnetic state at the interface between the two materials.
Abstract: Magnetoresistance measurements have been performed on epitaxial metal/ferromagnetic insulator bilayers. They are more sensitive to magnetic behavior at the interface of such structures than magnetization measurements. It is clear from the magnetoresistance data that previously reported slope discontinuities in the resistance versus temperature of such heterostructures are magnetic in origin. These studies demonstrate that the conduction electrons of the metal are coupled to the spins in the magnetic insulator, and act as probes of the magnetic state at the interface between the two materials. An example of the usefulness of this probe is shown by magnetoresistance measurements on a Ag/EuO bilayer.
TL;DR: In this article, the effect of adding praseodymium (Pr) to YBa 2 Cu 3 O 7 is shown to reduce T c and increase resistivity, where the magnetic field direction is rotated with respect to the crystalline c-axis of the films.
Abstract: The effect of adding praseodymium (Pr) to YBa 2 Cu 3 O 7 is to reduce T c and increase resistivity. We have measured the magnetoresistance in epitaxial films of YBa 2 Cu 3 O 7 and Y 0.8 Pr 0.2 Ba 2 Cu 3 O 7 in magnetic fields up to 5 T and temperatures between 50K and 90K. Large variations in the magnetoresistance are observed when the magnetic field direction is rotated with respect to the crystalline c-axis of the films. In the YBa 2 Cu 3 O 7 films the effect of decreasing the temperature is to move from a 2D picture close to T c where the effect of the magnetic field scales with the component perpendicular to the planes, to a less anisotropic behaviour at lower temperatures. For Y 0.8 Pr 0.2 Ba 2 Cu 3 O 7 the behaviour of the magnetoresistance is opposite. Here, increasing the temperature towards T c decreases the anisotropy.