Showing papers on "Colossal magnetoresistance published in 2000"
TL;DR: An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
Abstract: An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
1,916 citations
30 May 2000
TL;DR: In this paper, the fundamental features of CMR Manganites have been discussed, including Spin Dynamics and Electronic Structures, Materials Systematics and Lattice Effects, and Tunnelling Magnetoresistance.
Abstract: 1. Fundamental Features of CMR Manganites 2. Spin Dynamics and Electronic Structures 3. Materials Systematics and Lattice Effects 4. Tunnelling Magnetoresistance.
982 citations
TL;DR: A large electric-pulse-induced reversible resistance change active at room temperature and under zero magnetic field has been discovered in colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 thin films.
Abstract: A large electric-pulse-induced reversible resistance change active at room temperature and under zero magnetic field has been discovered in colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 thin films. Electric field-direction-dependent resistance changes of more than 1700% were observed under applied pulses of ∼100 ns duration and as low as ±5 V magnitude. The resistance changes were cumulative with pulse number, were reversible and nonvolatile. This electrically induced effect, observed in CMR materials at room temperature has both the benefit of a discovery in materials properties and the promise of applications for thin film manganites in the electronics arena including high-density nonvolatile memory.
945 citations
TL;DR: In this paper, a description of experimental results, old and new ones, in which a magnetoresistance was discovered, linear in magnetic field, was presented, and explained that there are two theoretical possibilities for such a phenomenon.
Abstract: A description is presented of experimental results, old and new ones, in which a magnetoresistance was discovered, linear in magnetic field. It is explained that there are two theoretical possibilities for such a phenomenon. The first one happens in a polycrystalline metal in a classically large field; it was known since the late 1950s. The other one is the so-called quantum magnetoresistance in semimetals and in some single crystalline metals having small pockets of the Fermi surface with a small effective mass.
311 citations
TL;DR: In this paper, the transverse resistance of an intermetallic compound was measured in pulsed high magnetic fields up to 25 T and the giant magnetoresistance was observed due to the field-induced magnetic transition from the antiferromagnetic to the intermediate phase at low temperatures.
Abstract: We have measured the transverse resistance of an intermetallic compound ${\mathrm{Mn}}_{3}\mathrm{GaC}$ in pulsed high magnetic fields up to 25 T. Giant magnetoresistance is observed due to the field-induced magnetic transition from the antiferromagnetic to the intermediate phase at low temperatures. The temperature dependence of magnetoresistance shows a dip at the Curie temperature. The dip can be explained using a simple model of de Gennes and Friedel based on magnetic critical scatterings. The normal Hall coefficient is found to show a striking change at the transition, suggesting that the giant magnetoresistance is caused by the change of the carrier concentration.
235 citations
TL;DR: It is argued that magnetoresistance can arise by a different mechanism in certain ferromagnets—quantum interference effects rather than simple scattering—and only weakly temperature-dependent below the Curie point.
Abstract: The desire to maximize the sensitivity of read/write heads (and thus the information density) of magnetic storage devices has stimulated interest in the discovery and design of new magnetic materials exhibiting magnetoresistance Recent discoveries include the 'colossal' magnetoresistance in the manganites and the enhanced magnetoresistance in low-carrier-density ferromagnets An important feature of these systems is that the electrons involved in electrical conduction are different from those responsible for the magnetism The latter are localized and act as scattering sites for the mobile electrons, and it is the field tuning of the scattering strength that ultimately gives rise to the observed magnetoresistance Here we argue that magnetoresistance can arise by a different mechanism in certain ferromagnets--quantum interference effects rather than simple scattering The ferromagnets in question are disordered, low-carrier-density magnets where the same electrons are responsible for both the magnetic properties and electrical conduction The resulting magnetoresistance is positive (that is, the resistance increases in response to an applied magnetic field) and only weakly temperature-dependent below the Curie point
198 citations
TL;DR: In this paper, the resistivity and magnetoresistance of a magnetite single crystal and Fe3 O4 films of various thicknesses were measured in the temperature range 70 K
Abstract: The resistivity and magnetoresistance of a magnetite single crystal and Fe3 O4 films of various thicknesses were measured in the temperature range 70 K
183 citations
TL;DR: In this article, the authors review the recent progress in the study of layered magnetic manganites La2−2xSr1+2xMn2O7, which have many unique features of charge transport and magnetism inherent to the quasi-two-dimensional electronic structure.
Abstract: ▪ Abstract We review the recent progress in the study of layered magnetic manganites La2−2xSr1+2xMn2O7, which have many unique features of charge transport and magnetism inherent to the quasi-two-dimensional electronic structure. The system shows a wide variety of magnetic-field-induced phenomena due to the layered crystal and magnetic structure, such as the highly anisotropic ferromagnetic metallic ground state, the colossal magnetoresistance (CMR) effect, and the tunneling-type magnetoresistance (TMR). The charge transport properties, as well as the magnetic ones, strongly depend on the carrier-doping level and the applied pressure, which reflects the variation of the orbital-dependent occupancy of itinerant eg-like electrons. Although the layered manganite is one of a new class of CMR materials, the study of this system may also reveal some of the key issues for understanding the CMR effect in mixed-valent manganese oxide.
168 citations
TL;DR: In this paper, a phase diagram of doped Mott insulators is constructed using a composition spread method for fabricating a film whose doping concentration varies from 0 to 1 continuously, and the concurrent x-ray diffractometer, scanning superconducting quantum interference device microscope and infrared optical spectroscopy are employed for characterizing the film.
Abstract: We propose a method of rapid construction of a structural–magnetic–electronic phase diagram of doped Mott insulators. The composition-spread method is utilized for fabricating a film whose doping concentration varies from 0 to 1 continuously. The concurrent x-ray diffractometer that measures x-ray diffraction spectra of all the composition simultaneously, the scanning superconducting quantum interference device microscope, and the infrared optical spectroscopy are employed for characterizing the film. A demonstration is given for a colossal magnetoresistive material, La1−xSrxMnO3.
162 citations
TL;DR: In this paper, the electrical transport properties of grain boundaries in epitaxial thin films of perovskite manganites have been studied as a function of temperature and applied magnetic field.
161 citations
TL;DR: In this article, measurements of magnetoresistance and magnetization were carried out on ceramic samples of La0.5Pb 0.5MnO3, containing 10 at.
Abstract: Measurements of magnetoresistance and magnetization were carried out on ceramic samples of La0.5Pb0.5MnO3 and La0.5Pb0.5MnO3, containing 10 at. % Ag in a dispersed form. The results obtained for the resistivity at zero applied magnetic field exhibit a shallow minimum at the temperature T∼25–30 K which shifts towards lower temperatures upon applying a magnetic field and disappears at a certain field Hcr. Also the resistivity at helium temperature decreases upon applying magnetic fields. It is shown that the model of charge carriers tunneling between antiferromagnetically coupled grains may account for the results observed.
TL;DR: In this article, the authors used molecular-beam-epitaxy growth techniques to synthesize ferromagnet/insulator/ferromagnetic trilayer heterostructures with the "colossal" magnetoresistance material La1−xSrxMnO3 as the ferromagnetic material.
Abstract: Using molecular-beam-epitaxy growth techniques, we have synthesized ferromagnet/insulator/ferromagnet trilayer heterostructures with the “colossal” magnetoresistance material La1−xSrxMnO3 as the ferromagnet. These trilayer films were fabricated into magnetic tunnel junctions which exhibit magnetoresistance ΔR/R(H) of as much as 450% in 200 Oe applied field at 14 K, and which persists up to ∼250 K. In situ reflection high-energy electron diffraction (RHEED) allows us to correlate the quality of the epitaxial growth with the magnetoresistive properties. Samples which showed signs of disorder in RHEED also exhibit disorder effects in low-temperature transport and have smaller magnetoresistance which vanishes at lower temperatures.
TL;DR: In this paper, the magnetic anisotropy of epitaxial colossal magnetoresistance (EGM) films on SrTiO3 substrates is dominated by the strain or magnetocrystalline anisotropic effects depending on the orientation of the film.
Abstract: The magnetic anisotropy of epitaxial colossal magnetoresistance films on SrTiO3 substrates is dominated by the strain or magnetocrystalline anisotropy depending on the orientation of the film. While the magnetic anisotropy of (001) films is determined by magnetocrystalline anisotropy, that of (110) films is determined by magnetoelastic effects. Furthermore while the microstructure in the thin films has a significant effect on the coercive field, it has a correspondingly negligible effect on the magnetic anisotropy. We find a roughening surface morphology with increasing thickness that is more pronounced in (110) oriented films and can be attributed to the growth kinetics.
TL;DR: In this paper, magnetic and magnetotransport experimental data in well-characterized small particles of La 0.67 Ca 0.33 MnO 3 are presented, and low-temperature resistivity upturn present in small particle size samples can be understood in terms of an electrostatic barrier between grains.
TL;DR: In this paper, the most important physical properties of manganites of the La-Ca-Mn-O type were analyzed and a discussion of the scientific problems encountered in the physics of the manganite transport was presented, where the main focus was on the peculiarities of these compounds reflected in their crystalline, electronic, and magnetic structures.
Abstract: An attempt is made to analyze the most important physical properties of manganites of the La-Ca-Mn-O type, which exhibit the colossal magnetoresistance effect. The primary focus is on the peculiarities of these compounds which are reflected in their crystalline, electronic, and magnetic structures and which determine the possible mechanisms by which an external magnetic field can exert a substantial influence on the transport characteristics of the current carriers in manganites. The combined effect of these factors is to create the necessary conditions for a metal-insulator phase transition that is sensitive to an external magnetic field. Another major topic in this review is a discussion of the scientific problems confronting the physics of manganites.
TL;DR: The stability of charge-orbital ordering in a colossal magnetoresistance (CMR) manganite can be varied to a large extent by doping of Cr impurities on the Mn site.
Abstract: The stability of charge-orbital ordering in a colossal magnetoresistance (CMR) manganite can be varied to a large extent by doping of Cr impurities on the Mn site. Most of the generic features seen in the CMR manganites, such as the submicrometric phase separation into metallic and insulating states, a resistivity-enhanced paramagnetic state, and related CMR effect, can be generated successively with Cr doping in ${\mathrm{Nd}}_{1/2}{\mathrm{Ca}}_{1/2}{\mathrm{MnO}}_{3}$ crystal. Systematic studies of the Cr-doped crystals by measurements of magnetotransport and x-ray diffraction have shown that the incommensurate charge-orbital-ordered state turns into the dynamic and short-range charge-orbital correlation that is the origin of the high-resistive state exhibiting CMR.
TL;DR: In this paper, an insulator-to-metal transition below 240 K is induced by applying a 7 T magnetic field in Pr0.5Ca0.1nO3 thin films grown by the pulsed laser deposition technique on [100]-SrTiO3 substrates.
Abstract: An insulator-to-metal transition below 240 K is induced by applying a 7 T magnetic field in Pr0.5Ca0.5MnO3 thin films grown by the pulsed laser deposition technique on [100]-SrTiO3 substrates. This value of the melting magnetic field, much lower that the one required in bulk (∼20 T), is assumed to be an effect of the tensile stress. These results confirm the importance of the bandwidth in the control of the physical properties of this compound and open the route to get colossal magnetoresistive properties by using strain effects.
TL;DR: In this article, the Monte Carlo method was used to study the ferromagnetic transition in three-dimensional double exchange models and the critical temperature T c was determined by finite-size scaling analysis.
Abstract: Ferromagnetic transition in three-dimensional double-exchange models is studied by the Monte Carlo method. Critical temperature T c is precisely determined by finite-size scaling analysis. Strong spin fluctuations in this itinerant system significantly reduce T c from mean-field estimates. By choosing appropriate parameters, obtained values of T c quantitatively agree with experiments for the ferromagnetic metal regime of (La,Sr)MnO 3 , which is a typical perovskite manganite showing colossal magnetoresistance. This indicates that the double-exchange mechanism alone is sufficient to explain T c in this material. Critical exponents are also discussed.
TL;DR: In this article, a study of magnetocaloric effect in the colossal magnetoresistance material La 2/3 Ca 1/3 MnO 3 was presented, which suggests that perovskite manganites are suitable candidates as working substances in magnetic refrigeration technology.
TL;DR: In this article, the magnetization in ordered double perovskite alloy, Sr2Fe(W1−xMox)O6, was investigated for polycrystals.
TL;DR: The double perovskite Sr 2 CrMoO 6 with Cr 3+ O-Mo 5+ pairs is ferrimagnetic (T N =450 K), but there is considerable site disorder as mentioned in this paper.
TL;DR: In this paper, a mixture of the two samples was annealed at 800 °C and the scanning electron micrograph shows large CoFe2O4 grains well surrounded by La0.7Sr0.3MnO3 grains.
Abstract: La0.7Sr0.3MnO3 and CoFe2O4 samples have been prepared by a sol-gel process. A mixture of the two samples was annealed at 800 °C and the scanning electron micrograph shows large CoFe2O4 grains well surrounded by La0.7Sr0.3MnO3 grains. The powder x-ray diffraction patterns indicate no evidence of reaction between the La0.7Sr0.3MnO3 and CoFe2O4. The resistivity of the combined sample (with 20 wt% CoFe2O4) is about an order of magnitude larger than that of the same-grain-sized La0.7Sr0.3MnO3 sample, while a large low field magnetoresistance (MR) has been obtained in the combined samples. Under an applied field of 5 kOe, the MR of the combined sample is 10% even at 280 K and 5% at 290 K, whereas the same nanosized La0.7Sr0.3MnO3 sample is only 2% and 1%, respectively.
TL;DR: In this paper, a series of La0.75Sr0.25MnO3 films with thickness ranging from 32 to 3300 A were fabricated using pulsed laser deposition onto SrTiO3 and LaAlO3 substrates.
Abstract: We present results on magnetotransport measurements of a series of La0.75Sr0.25MnO3 films with thickness ranging from 32 to 3300 A. Films were fabricated using pulsed laser deposition onto SrTiO3 and LaAlO3 substrates. The substrate-film lattice mismatch causes strain in ultrathin films which diminishes with increasing thickness. Ultrathin films exhibit perfect match of in-plane film and substrate lattice parameters. The inhomogeneity of lattice parameters in thick films is caused by film-substrate mismatch strain and displayed by nonuniform broadening of x-ray diffraction Bragg reflections. The observation of characteristic Kiessig fringes is evidence for very uniform thickness of fabricated films. We found that the magnetotransport properties are strongly controlled by the film thickness and that allowed us to tailor the temperature of the metal-to-semiconductor phase transition in the range of 100–340 K with a change in magnetoresistivity within a factor of 3. We also present comparisons between the th...
TL;DR: In this paper, the magnetic properties of the colossal magnetoresistance ferromagnet Ndo(0.7)Sr( 0.3)MnO(3) have been explored by ac-susceptibilities and dc-magnetization measurements.
Abstract: Dynamic magnetic properties of the colossal magnetoresistance ferromagnet Ndo(0.7)Sr(0.3)MnO(3) have been explored by ac-susceptibilities and dc-magnetization measurements. The system orders magnetically below T(c)approximate to 235 K with a large differe
TL;DR: In this article, a theory of the renormalization of the magnetic excitation spectrum in colossal magnetoresistance compounds was proposed based on the modulation of magnetic exchange bonds by the orbital degree of freedom of double-degenerate electrons.
Abstract: In metallic manganites with low Curie temperatures, a peculiar softening of the magnon spectrum close to the magnetic zone boundary has experimentally been observed. Here we present a theory of the renormalization of the magnetic excitation spectrum in colossal magnetoresistance compounds. The theory is based on the modulation of magnetic exchange bonds by the orbital degree of freedom of double-degenerate ${e}_{g}$ electrons. The model considered is an orbitally degenerate double-exchange system coupled to Jahn-Teller active phonons which we treat in the limit of strong on-site repulsions. Charge and coupled orbital-lattice fluctuations are identified as the main origin of the unusual softening of the magnetic spectrum.
TL;DR: The strong coupling of the parallel field to the orbital motion arising from the finite layer thickness and the large Fermi wavelength of the quasi-two-dimensional system at low carrier densities is explained.
Abstract: We provide a possible theoretical explanation for the recently observed giant positive magnetoresistance in high mobility low density quasi-two-dimensional electron and hole systems. Our explanation is based on the strong coupling of the parallel field to the orbital motion arising from the finite layer thickness and the large Fermi wavelength of the quasi-two-dimensional system at low carrier densities.
TL;DR: In this paper, the Monte Carlo method was used to study the ferromagnetic transition in three-dimensional double-exchange models and the critical temperature was determined by finite-size scaling analysis.
Abstract: Ferromagnetic transition in three-dimensional double-exchange models is studied by the Monte Carlo method. Critical temperature $T_{\rm c}$ is precisely determined by finite-size scaling analysis. Strong spin fluctuations in this itinerant system significantly reduce $T_{\rm c}$ from mean-field estimates. By choosing appropriate parameters, obtained values of $T_{\rm c}$ quantitatively agree with experiments for the ferromagnetic metal regime of (La,Sr)MnO$_{3}$, which is a typical perovskite manganite showing colossal magnetoresistance. This indicates that the double-exchange mechanism alone is sufficient to explain $T_{\rm c}$ in this material. Critical exponents are also discussed.
TL;DR: In this paper, the temperature and field dependence of anisotropic magnetoresistance (AMR) in fully strained tetragonal thin films of the manganite La0.7Ca0.3MnO3 was investigated.
Abstract: We report the temperature and field dependence of anisotropic magnetoresistance (AMR) in fully strained tetragonal thin films of the colossal magnetoresistance manganite La0.7Ca0.3MnO3. The behavior of the AMR is very different from that found in conventional metallic alloys. Its magnitude is peaked near the Curie temperature TC and becomes small at low temperature. It has two distinct symmetry components: one twofold symmetric about the transport current direction dominant near TC, the other fourfold symmetric with symmetry axes of the crystal, appearing at low temperature.
TL;DR: In this article, the effect of Mn site substitution by Co and Cr on the magnetotransport properties of ceramic samples was systematically investigated as a function of doping, and the existence of an optimum doping level that enhances magnetoresistance was also found.
Abstract: In this paper we show the effect of Mn site substitution $(l~10%)$ by Co and Cr on the magnetotransport properties of ceramic samples of ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}.$ Resistivity, magnetization, and magnetoresistance were systematically investigated as a function of doping. An increase in resistivity and a diminution of metal-insulator transition and Curie temperatures was observed as a consequence of both Co and Cr doping. The evolution of the number of neighbors ferromagnetically coupled to Mn was studied in each sample, and the results suggest some degree of ferromagnetic coupling between ${\mathrm{Cr}}^{3+}$ and Mn ions. Implications of both ferromagnetic Cr ${}^{3+}\ensuremath{-}\mathrm{O}\ensuremath{-}{\mathrm{Mn}}^{3+}$ superexchange and double exchange interactions are discussed. We also found the existence of an optimum doping level that enhances colossal magnetoresistance. This has been explained considering electron localization due to magnetic disorder induced by doping in the Mn site.
TL;DR: In this article, an itinerant type of ferromagnetic order, stable up to temperatures of the order of 600}900 K, is established for hexaborides with divalent cations.
Abstract: Various recent experimental investigations have revealed unusual magnetic properties of hexaborides with divalent cations M2‘. EuB 6 is ferromagnetic below 16 K and its low-temperature properties show remarkable similarities to those of manganese oxides, exhibiting the phenomenon of colossal magnetoresistance. Close to the phase transition as well as far below the ordering temperature, EuB 6 exhibits anomalous features, that are brie#y discussed. Alkaline-earth hexaborides are close to a metal}insulator transition and it has been found that, in a narrow range of electron doping, an itinerant-type of ferromagnetic order, stable up to temperatures of the order of 600}900 K, is established. This remarkable phenomenon is suspected to be due to the peculiar electronic band structure of these materials. ( 2000 Elsevier Science B.V. All rights reserved.