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G. Q. Gong

Bio: G. Q. Gong is an academic researcher. The author has contributed to research in topics: Magnetoresistance & Colossal magnetoresistance. The author has an hindex of 3, co-authored 3 publications receiving 837 citations.

Papers
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Journal ArticleDOI
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.

354 citations

Journal ArticleDOI
TL;DR: In this paper, a trilayer epitaxial thin film device based on the doped perovskite manganates La-Ca-Mn-O and La-Sr-mn−O was constructed and large resistance changes, up to a factor of 2, can be induced by a moderate applied magnetic field below 200 Oe in these trilayers supporting current-perpendicular-to-plane transport.
Abstract: We report on the fabrication of a new class of trilayer epitaxial thin film devices based on the doped perovskite manganates La–Ca–Mn–O and La–Sr–Mn–O. We show that large resistance changes, up to a factor of 2, can be induced by a moderate applied magnetic field below 200 Oe in these trilayers supporting current‐perpendicular‐to‐plane transport. These results show that low‐field spin‐dependent transport in manganates can be accomplished, the magnitude of which is suitable for magnetoresistive field sensors.

348 citations

Journal ArticleDOI
TL;DR: The record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system.
Abstract: Record values of colossal magnetoresistance (CMR) have been achieved in the antiferromagnetic phase of the La1−xCaxMnO3 system. At 125 K, the CMR of the La0.5Ca0.5MnO3 reaches nearly 1 000 000%. It increases exponentially to 100 000 000% at 57 K. While the ground state is primarily an antiferromagnet, application of a magnetic field induces a ferromagnetic alignment of spins that is highly beneficial to the electron conduction. Other ferromagnetic samples exhibit very sharp magnetic phase transitions, with which the magnetotransport is closely correlated.

157 citations


Cited by
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Journal ArticleDOI
15 Oct 1998-Nature
TL;DR: In this paper, an ordered double perovskite (Sr2FeMoO) was shown to exhibit intrinsic tunnelling-type magnetoresistance at room temperature.
Abstract: Colossal magnetoresistance—a huge decrease in resistance in response to a magnetic field—has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view1. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the charge carriers, caused by the half-metallic nature of these materials20,21; this in principle allows spin-dependent carrier scattering processes, and hence the resistance, to be strongly influenced by low magnetic fields. This type of field control has been demonstrated for charge-carrier scattering at tunnelling junctions2,3 and at crystal-twin or ceramic grain boundaries4,5, although the operating temperature of such structures is still too low (⩽150 K) for most applications. Here we report a material—Sr2FeMoO6, an ordered double perovskite6—exhibiting intrinsic tunnelling-type magnetoresistance at room temperature. We explain the origin of this behaviour with electronic-structure calculations that indicate the material to be half-metallic. Our results show promise for the development of ordered perovskite magnetoresistive devices that are operable at room temperature.

2,065 citations

Journal ArticleDOI
01 Sep 1997
TL;DR: In this paper, the authors review recent experimental work falling under the broad classification of colossal magnetoresistance (CMR), which is magnetoreduction associated with a ferromagnetic-toparamagnetic phase transition.
Abstract: We review recent experimental work falling under the broad classification of colossal magnetoresistance (CMR), which is magnetoresistance associated with a ferromagnetic-toparamagnetic phase transition. The prototypical CMR compound is derived from the parent compound, perovskite LaMnO 3. When hole doped at a concentration of 20–40% holes/Mn ion, for instance by Ca or Sr substitution for La, the material displays a transition from a high-temperature paramagnetic insulator to a low-temperature ferromagnetic metal. Near the phase transition temperature, which can exceed room temperature in some compositions, large magnetoresistance is observed and its possible application in magnetic recording has revived interest in these materials. In addition, unusual magneto-elastic effects and charge ordering have focused attention on strong electron–phonon coupling. This coupling, which is a type of dynamic extended-system version of the Jahn–Teller effect, in conjunction with the double-exchange interaction, is also viewed as essential for a microscopic description of CMR in the manganite perovskites. Large magnetoresistance is also seen in other systems, namely Tl 2Mn2O7 and some Cr chalcogenide spinels, compounds which differ greatly from the manganite perovskites. We describe the relevant points of contrast between the various CMR materials.

1,336 citations

Journal ArticleDOI
26 Sep 2002-Nature
TL;DR: It is found that a minimum thickness of five LaTiO3 layers is required for the centre titanium site to recover bulk-like electronic properties, and this represents a framework within which the short-length-scale electronic response can be probed and incorporated in thin-film oxide heterostructures.
Abstract: The nature and length scales of charge screening in complex oxides are fundamental to a wide range of systems, spanning ceramic voltage-dependent resistors (varistors), oxide tunnel junctions and charge ordering in mixed-valence compounds. There are wide variations in the degree of charge disproportionation, length scale, and orientation in the mixed-valence compounds: these have been the subject of intense theoretical study, but little is known about the microscopic electronic structure. Here we have fabricated an idealized structure to examine these issues by growing atomically abrupt layers of LaTi(3+)O(3) embedded in SrTi(4+)O(3). Using an atomic-scale electron beam, we have observed the spatial distribution of the extra electron on the titanium sites. This distribution results in metallic conductivity, even though the superlattice structure is based on two insulators. Despite the chemical abruptness of the interfaces, we find that a minimum thickness of five LaTiO(3) layers is required for the centre titanium site to recover bulk-like electronic properties. This represents a framework within which the short-length-scale electronic response can be probed and incorporated in thin-film oxide heterostructures.

829 citations

Journal ArticleDOI
TL;DR: The manganese oxides of general formula RE1−xMxMnO3 (RE = rare earth, M = Ca, Sr, Ba, Pb) have remarkable interrelated structural, magnetic and transport properties induced by the mixed valence (3+−4+) of the Mn ions.
Abstract: The manganese oxides of general formula RE1−xMxMnO3 (RE = rare earth, M = Ca, Sr, Ba, Pb) have remarkable interrelated structural, magnetic and transport properties induced by the mixed valence (3+–4+) of the Mn ions. In particular, they exhibit very large negative magnetoresistance, called colossal magnetoresistance (CMR), in the vicinity of metal–insulator transition for certain compositions. In this review paper, we summarize the most important features of the physics of the CMR manganites. The growth techniques for manganese oxide thin films, which are the basic material for potential applications, are reviewed and their structure and morphology examined in relation to growth parameters. The effects of epitaxial strains on the physical properties are discussed. Early works on superlattices and devices are presented.

775 citations

Journal ArticleDOI
21 May 2003
TL;DR: The magnetic tunnel junction (MTJ) as discussed by the authors is an example of spintronic materials in which the flow of spin-polarized electrons is manipulated by controlling, via magnetic fields, the orientation of magnetic moments in inhomogeneous magnetic thin film systems.
Abstract: The discovery of enhanced magnetoresistance and oscillatory interlayer exchange coupling in transition metal multilayers just over a decade ago has enabled the development of new classes of magnetically engineered magnetic thin-film materials suitable for advanced magnetic sensors and magnetic random access memories. Magnetic sensors based on spin-valve giant magnetoresistive (GMR) sandwiches with artificial antiferromagnetic reference layers have resulted in enormous increases in the storage capacity of magnetic hard disk drives. The unique properties of magnetic tunnel junction (MTJ) devices has led to the development of an advanced high performance nonvolatile magnet random access memory with density approaching that of dynamic random-access memory (RAM) and read-write speeds comparable to static RAM. Both GMR and MTJ devices are examples of spintronic materials in which the flow of spin-polarized electrons is manipulated by controlling, via magnetic fields, the orientation of magnetic moments in inhomogeneous magnetic thin film systems. More complex devices, including three-terminal hot electron magnetic tunnel transistors, suggest that there are many other applications of spintronic materials.

591 citations