Showing papers on "Charge ordering published in 2003"
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
TL;DR: This work is able to correlate the structural features in the series of single-phase materials Li(3-y)V(2)(PO(4))(3) with the electrochemical voltage-composition profile, highlighting the importance of ion-ion interactions in determining phase transitions in these materials.
Abstract: Monoclinic lithium vanadium phosphate, alpha-Li(3)V(2)(PO(4))(3), is a highly promising material proposed as a cathode for lithium-ion batteries. It possesses both good ion mobility and high lithium capacity because of its ability to reversibly extract all three lithium ions from the lattice. Here, using a combination of neutron diffraction and (7)Li MAS NMR studies, we are able to correlate the structural features in the series of single-phase materials Li(3-y)V(2)(PO(4))(3) with the electrochemical voltage-composition profile. A combination of charge ordering on the vanadium sites and lithium ordering/disordering among lattice sites is responsible for the features in the electrochemical curve, including the observed hysteresis. Importantly, this work highlights the importance of ion-ion interactions in determining phase transitions in these materials.
498 citations
TL;DR: The low and high-temperature structures of La2CoMnO6 and La2NiMnNO6 have been refined using powder neutron diffraction as mentioned in this paper.
Abstract: The low-and high-temperature structures of La2CoMnO6 and La2NiMnO6 have been refined using powder neutron diffraction. At low temperatures the materials adopt a charge-ordered monoclinic structure which transforms to a rhombohedral structure at elevated temperature without loss of charge ordering. This charge ordering scheme allows us for the first time to rationalize the relationships between the physical and structural properties of these materials.
274 citations
TL;DR: Charge ordering of vanadium (V3+/V4+) was observed in Li2V2(PO4)3 as shown by the gray and blue V-O octahedra, respectively, indicating that the electrons are pinned in this phase and hence transport is limited.
Abstract: The delithiation process in monoclinic Li3V2(PO4)3 has been determined by powder neutron diffraction coupled with 7Li solid-state NMR techniques. Charge ordering of vanadium (V3+/V4+) was observed in Li2V2(PO4)3 as shown by the gray and blue V−O octahedra, respectively, indicating that the electrons are pinned in this phase and hence transport is limited.
242 citations
TL;DR: In this paper, the structural and magnetic phase diagram of the manganites La1−xAgxMnO3 shows similarity with the La 1−x′Srx′McNO3 series, involving a metallic ferromagnetic domain at relatively high temperature (≈300 K).
129 citations
TL;DR: In this article, the electronic structure of charge-ordered magnetite (Fe 3 O 4 ) below the Verwey transition and Mn-, Co-, or Ni-substituted Fe 3 o 4 was investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band-structure method.
Abstract: The electronic structure of charge-ordered magnetite (Fe 3 O 4 ) below the Verwey transition and Mn-, Co-, or Ni-substituted Fe 3 O 4 are investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band-structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+ U approach, for which the charge ordering is found to be a stable solution in contrast to a metallic state given by the LSDA. The x-ray absorption spectra as well as the x-ray magnetic circular dichroism spectra at the K, L 2 , 3 , and M 2 , 3 edges for transition metal sites are calculated. A good agreement between theory and experiment is obtained.
126 citations
TL;DR: In this paper, the properties of the perovskites NdBaCo 2 O 5+ δ have been studied as a function of temperature by neutron powder diffraction and long-range G-type antiferromagnetic order is realized for all samples apart from that with δ = 0.5.
116 citations
TL;DR: A recent vast experimental and theoretical effort in manganites has shown that the magnetoresistance effect can be understood based on the competition of charge-ordered and ferromagnetic phases as discussed by the authors.
114 citations
TL;DR: In this article, phase diagrams of charge order patterns of the θ-phase organic conductors were investigated on the basis of the static-limit extended Hubbard model including the second nearest Coulomb repulsion.
Abstract: Phase diagrams of charge order patterns of the θ-phase organic conductors are investigated on the basis of the static-limit extended Hubbard model including the second nearest Coulomb repulsion V '...
86 citations
TL;DR: In this article, the authors report on peculiar metamagnetic transitions which take place in antiferromagnetic, charge and orbitally ordered manganites at very low temperatures, the virgin magnetization curves of some of these compounds exhibit several, sharp steps giving rise to a staircase-like shape.
78 citations
TL;DR: YBaFe(2)O(5) was synthesized by heating a nanoscale citrate precursor in a carefully controlled reducing environment as discussed by the authors, which can only be achieved in a narrow window of oxygen partial pressures and temperatures.
Abstract: YBaFe(2)O(5) has been synthesized by heating a nanoscale citrate precursor in a carefully controlled reducing environment. Successful synthesis of a single-phase sample can only be achieved in a narrow window of oxygen partial pressures and temperatures. YBaFe(2)O(5) adopts an oxygen-deficient perovskite-type structure, which contains double layers of corner sharing FeO(5) square pyramids separated by Y(3+) ions. At T(N) congruent with 430 K, tetragonal (P4/mmm) and paramagnetic YBaFe(2)O(5) orders antiferromagnetically (AFM) experiencing a slight orthorhombic distortion (Pmmm). Around this temperature, it can be characterized as a class-III mixed valence (MV) compound, where all iron atoms exist as equivalent MV Fe(2.5+) ions. The magnetic structure is characterized by AFM Fe-O-Fe superexchange coupling within the double layers and a ferromagnetic Fe-Fe direct-exchange coupling between neighboring double layers. Upon cooling below approximately 335 K, a premonitory charge ordering (2Fe(2.5+) --> Fe(2.5+delta) + Fe(2.5)(-delta)) into a class-II MV phase takes place. This transition is detected by differential scanning calorimetry, but powder diffraction techniques fail to detect any volume change or a long-range structural order. At approximately 308 K, a complete charge ordering (2Fe(2.5+) --> Fe(2+) + Fe(3+)) into a class-I MV compound takes place. This charge localization triggers a number of changes in the crystal, magnetic, and electronic structure of YBaFe(2)O(5). The magnetic structure rearranges to a G-type AFM structure, where both the Fe-O-Fe superexchange and the Fe-Fe direct-exchange couplings are antiferromagnetic. The crystal structure rearranges (Pmma) to accommodate alternating chains of Fe(2+) and Fe(3+) running along b and an unexpectedly large cooperative Jahn-Teller distortion about the high-spin Fe(2+) ions. This order of charges does not fulfill the Anderson condition, and it rather corresponds to an ordering of doubly occupied Fe(2+) d(xz) orbitals. Comparisons with YBaMn(2)O(5) and YBaCo(2)O(5) are made to highlight the impact of changing the d-electron count.
TL;DR: In this paper, the authors employed Landau's phenomenological theory for second-order phase transitions in inhomogeneously mixed-valence compounds of localized 3d or 4f-electron systems.
Abstract: Charge fluctuation and charge-ordering phenomena in compounds based on the 3d electrons of transition-metal ions and 4f electrons of rare-earth ions are reviewed with particular emphasis on the mutual coupling of charge and lattice degrees of freedom. For the description of charge ordering in inhomogeneously mixed-valence compounds of localized 3d or 4f-electron systems, we employ Landau's phenomenological theory for second-order phase transitions. By use of the group-theoretical method, the charge fluctuation mode corresponding to the active representation for the second-order transition is determined. The localization of 3d and 4f electrons makes the valence for the specific ions an integer number of charge units e in the ordered phases at low temperatures. The elastic soft mode observed by the ultrasonic method is often a useful indication for the charge fluctuation mode that is frozen below the charge-ordering point T C. The transverse c44 mode exhibiting a considerable softening in the rare-earth com...
TL;DR: In this paper, the ground-state phase diagram of the one-dimensional 'ionic' Hubbard model with an alternating periodic potential at half-filling by numerical diagonalization of finite systems with the Lanczos and density matrix renormalization group methods is investigated.
Abstract: We investigate the ground-state phase diagram of the one-dimensional 'ionic' Hubbard model with an alternating periodic potential at half-filling by numerical diagonalization of finite systems with the Lanczos and density matrix renormalization group methods. We identify an insulator–insulator phase transition from a band to a correlated insulator with simultaneous charge and bond-charge order. The transition point is characterized by the vanishing of the optical excitation gap while simultaneously the charge and spin gaps remain finite and equal. Indications for a possible second transition into a Mott-insulator phase are discussed.
TL;DR: In this article, the authors show that the optical conductivity of superconducting salt compounds is consistent with the observed low-frequency feature of the Coulomb repulsion, and they argue that the different optical responses observed are a consequence of the proximity of these compounds to a charge-ordering transition driven by the intermolecular Coulomb attraction.
Abstract: While the optical properties of the superconducting salt {alpha}-(BEDT-TTF){sub 2}-NH{sub 4}Hg(SCN){sub 4} remain metallic down to 2 K, in the nonsuperconducting K analog a pseudogap develops at frequencies of about 200 cm-1 for temperatures T<200 K. We show that the optical conductivity calculated with exact-diagonalization techniques on an extended Hubbard model at quarter filling is consistent with the observed low-frequency feature. We argue that the different optical responses observed are a consequence of the proximity of these compounds to a charge-ordering transition driven by the intermolecular Coulomb repulsion.
TL;DR: In this article, the possible charge-ordered patterns of three typical organic conductors (X =ReO 4, SbF 6 and Br) from the microscopic point of view are discussed.
Abstract: ESR investigations were performed for a series of quasi-one-dimensional organic conductors, (TMTTF) 2 X . The ESR linewidth shows abrupt jumps or humps in the paramagnetic insulating region. The (TMTTF) 2 X salts are roughly divided into three groups according to the anisotropy of the ESR linewidth at low temperatures. In this paper, we discuss the possible charge-ordered patterns of three typical salts ( X =ReO 4 , SbF 6 and Br) from the microscopic point of view.
TL;DR: The perovskite La1/3Sr2/3FeO3−δ was investigated by neutron diffraction, magnetic and Mossbauer spectroscopy measurements as mentioned in this paper.
Abstract: The perovskite La1/3Sr2/3FeO3−δ was investigated by neutron diffraction, magnetic and Mossbauer spectroscopy measurements. La1/3Sr2/3FeO3−δ undergoes magnetic ordering at T = 190–200 K accompanied by charge disproportionation. Magnetic peaks due to charge ordering are observed below 200 K. The charge ordering is gradually developed below 200 K along with a charge disproportionation, 2Fe4+ Fe3+ + Fe5+. La1/3Sr2/3FeO3−δ shows an antiferromagnetic structure at low temperature. Magnetic moments of about 3 and 1.3 μB were obtained from the neutron diffraction data refinement for Fe3+ and Fe5+ at 15 K, respectively, which suggest that both Fe ions are in a low spin state. These values are significantly lower than those reported by Battle et al for La1/3Sr2/3FeO2.98. Mossbauer spectra indicate that full charge ordering might be reached below 20 K with no Fe4+.
TL;DR: A comparison of the magnetic and structural features of RBaFe(2)O(5) compounds is included in order to illustrate how structural tuning, via changes in the radius of the rare-earth ion, can be used to alter the physical properties of these double-cell perovskites.
Abstract: Charge, orbital, and magnetic ordering of NdBaFe(2)O(5) and HoBaFe(2)O(5), the two end-members of the double-cell perovskite series RBaFe(2)O(5), have been characterized over the temperature range 2-450 K, using differential scanning calorimetry, neutron thermodiffractometry and high-resolution neutron powder diffraction Upon cooling, both compounds transform from a class-III mixed valence (MV) compound, where all iron atoms exist as equivalent MV Fe(25+) ions, through a "premonitory" charge ordering into a class-II MV compound, and finally to a class-I MV phase at low-temperature The latter phase is characterized by Fe(2+)/Fe(3+) charge ordering as well as orbital ordering of the doubly occupied Fe(2+) d(xz) orbitals The relative simplicity of the crystal and magnetic structure of the low-temperature charge-ordered state provide an unusual opportunity to fully characterize the classical Verwey transition, first observed in magnetite, Fe(3)O(4) Despite isotypism of the title compounds at high temperature, neutron diffraction analysis reveals striking differences in their phase transitions In HoBaFe(2)O(5), the Verwey transition is accompanied by a reversal of the direct Fe-Fe magnetic coupling across the rare earth layer, from ferromagnetic in the class-II and -III MV phases to antiferromagnetic in the low-temperature class-I MV phase In NdBaFe(2)O(5), the larger Nd(3+) ion increases the Fe-Fe distance, thereby weakening the Fe-Fe magnetic interaction This decouples the charge and magnetic ordering so that the Fe-Fe interaction remains ferromagnetic to low temperature Furthermore, the symmetry of the charge-ordered class-I MV phase is reduced from Pmma to P2(1)()ma and the magnitude of the orbital ordering is diminished These changes destabilize the charge-ordered state and suppress the temperature at which the Verwey transition occurs A comparison of the magnetic and structural features of RBaFe(2)O(5) compounds is included in order to illustrate how structural tuning, via changes in the radius of the rare-earth ion, can be used to alter the physical properties of these double-cell perovskites
TL;DR: In this article, the electronic properties of quarter-filled organic materials showing spin-Peierls transition are investigated theoretically and numerically by studying the one-dimensional extended Peierls-Hubbard model analytically as well as numerically.
Abstract: The electronic properties of quarter-filled organic materials showing spin–Peierls transition are investigated theoretically. By studying the one-dimensional extended Peierls–Hubbard model analytically as well as numerically, we find that there is a competition between two different spin–Peierls states due to the tetramized lattice distortion in the strongly correlated regime. One is accompanied by lattice dimerization which can be interpreted as a spontaneous Mott insulator, while the other shows the existence of charge order of Wigner crystal-type. Results of numerical density matrix renormalization group computations on sufficiently large system sizes show that the latter is stabilized in the ground state when both the on-site and the inter-site Coulomb interactions are large.
TL;DR: The dynamical properties of an extended Hubbard model, which is relevant to quarter-filled layered organic molecular crystals, are analyzed in this paper, using Lanczos diagonalization and large-N techniques.
Abstract: The dynamical properties of an extended Hubbard model, which is relevant to quarter-filled layered organic molecular crystals, are analyzed We have computed the dynamical charge correlation function, spectral density, and optical conductivity using Lanczos diagonalization and large-N techniques As the ratio of the nearest-neighbor Coulomb repulsion, V, to the hopping integral, t, increases there is a transition from a metallic phase to a charge-ordered phase Dynamical properties close to the ordering transition are found to differ from the ones expected in a conventional metal Large-N calculations display an enhancement of spectral weight at low frequencies as the system is driven closer to the charge-ordering transition in agreement with Lanczos calculations As V is increased the charge correlation function displays a collective mode which, for wave vectors close to (pi,pi), increases in amplitude and softens as the charge-ordering transition is approached We propose that inelastic x-ray scattering be used to detect this mode Large-N calculations predict superconductivity with d(xy) symmetry close to the ordering transition We find that this is consistent with Lanczos diagonalization calculations, on lattices of 20 sites, which find that the binding energy of two holes becomes negative close to the charge-ordering transition
TL;DR: In this article, the effects of Bi, Cr, and Fe doping on phase separation of La067Ca033MnO3 have been experimentally studied, and the effect of the substitution of Cr for Mn in this case promoted the ferromagnetic (FM) phase and charge-ordered antiferromagnetic phase, but its effects are significantly different for the two magnetic states.
Abstract: Effects of Bi, Cr, and Fe doping on phase separation of La067Ca033MnO3 have been experimentally studied As proved by the electron-spin resonance and neutron-diffraction studies, partial replacement of La by Bi causes the simultaneous occurrence of ferromagnetic (FM) phase and charge-ordered antiferromagnetic phase As a consequence, two subsequent magnetic transitions at similar to120 K and similar to230 K are resulted A strong coupling between the coexisted phases is assumed, which is responsible for the insensitivity of T-c(L), the higher Curie temperature, to Bi doping after the appearance of phase separation, and consistent with the discontinuous variation of T-c(L) with Cr doping As expected, the substitution of Cr for Mn in this case promotes the FM order, but its effects are significantly different for the two magnetic states Each Cr drives similar to100 neighboring unit cells, for the high-moment state, and similar to60 unit cells, for the low-moment state, into the FM state Two definite processes can be identified for the melting of the charge-ordered phase The FM fraction increases rapidly in the initial stage of Cr doping, and then slowly when the FM population exceeds similar to90% This could be a common feature of the phase-separated system suffering from random-phase fluctuation according to a theoretical analysis Exactly opposite effects on phase constituent are produced by Cr doping and Bi doping, and 1% Cr are equivalent to similar to46% Bi In contrast, both Cr doping and magnetic field promote the FM order 1% Cr correspond to a field of similar to45 T for the low-moment state and 6 T for the high-moment state, reducing the energy difference between the charge ordering and the FM states by similar to096 meV/Mn and similar to13 meV/Mn, respectively
TL;DR: In this article, it was shown that a first-order phase transition taking place at ∼ T V at ambient pressure opens a small gap within the oxygen p-band, resulting in the observed insulating state at T > T V.
TL;DR: In this article, experimental evidences of the charge ordering with the use of 13 C -NMR techniques in various organic conductors are reviewed and a new type of charge ordering in a TTM-TTP salt with one-dimensional half-filled band is suggested.
TL;DR: Temperature dependent optical spectra and the presence of a midinfrared band strongly suggest that the charge carriers in beta-Na0.33V2O5 are small polarons.
Abstract: Temperature dependent optical spectra are reported for beta-Na0.33V2O5. The sodium ordering transition at T-Na=240 K and, in particular, the charge ordering transition at T-MI=136 K strongly influence the optical spectra. The metal-insulator transition at T-MI leads to the opening of a pseudogap (homega=1700 cm(-1)) and to the appearance of a large number of optical phonons. These observations and the presence of a midinfrared band (typical for low dimensional metals) strongly suggest that the charge carriers in beta-Na0.33V2O5 are small polarons.
TL;DR: In this paper, transmission electron microscopy (TEM) and powder neutron diffraction experiments were performed on an A -site ordered manganese perovskite YBaMn 2 O 6 which undergoes unusual and multiple phase transitions.
Abstract: We performed transmission electron microscopy (TEM) and powder neutron diffraction experiments on an A -site ordered manganese perovskite YBaMn 2 O 6 which undergoes unusual and multiple phase transitions. In the paramagnetic insulating phase, the so-called CE type of charge and orbital ordering was observed in the monoclinic a – b plane, which has been frequently observed for the ordinary solid solution of A 1- x 3+ A x ′2+ MnO 3 around x =0.5. TEM revealed, however, a fourfold periodicity along the c axis, suggesting a new stacking pattern, in which planes of the CE type are built up according to the sequence [ααββ...]. Interestingly, when the system entered the antiferromagnetic state below 195 K, this stacking pattern changed into [αααα...] or [αβαβ...], suggesting a close interplay between spins and orbitals. The obtained stacking patterns were strongly correlated to the inherent structural alternation, i.e., the Y/Ba order along the c axis.
TL;DR: In this article, the modulated structure of BEDT-TTF 2 RbM'(SCN) 4 ; (M'=Zn, Co) was investigated by X-ray diffraction method.
TL;DR: In this paper, the authors studied the charge ordering transition of LiMn2O4 by means of anelastic spectroscopy, measuring the Young's modulus and the elastic energy loss function.
Abstract: We studied the charge ordering transition of LiMn2O4 by means of anelastic spectroscopy, measuring the Young’s modulus, E � ,a nd the elastic energy loss function, Q −1 .O ur measurements confirm the occurrence of a phase transition at 296 K on cooling, showing a large hysteresis on heating. The anelastic spectroscopy results also indicate that the transformation i sc har acterized by th ec oexistence of two phases. The shape of the real part of the Young’s modulus seems to indicate that the elastic constant which is more strongly affected by the transition is c44, like in the case of Fe3O4 .T hetime evolution
TL;DR: In this paper, the resistivity, magnetization, specific heat, shear modulus, and internal friction in the charge-ordered (CO) La 0.25Ca 0.75MnO3 were studied.
Abstract: The resistivity, magnetization, specific heat, shear modulus, and internal friction in the charge-ordered (CO) La0.25Ca0.75MnO3 were studied. The electronic conduction in the CO state was found to obey Mott's variable-range hopping model with a change in the localization length ξ near TN. A large decrease of the magnetization was observed between the Neer temperature TN and the charge ordering transition temperature TCO, which was attributed to the consequence of the orbital ordering. Drastic stiffening in shear modulus and an internal friction peak appeared just below TCO, and were explained as due to the coupling between the lattice strain and the orbital degree of freedom. A small upturn of the magnetization and a small softening of the ultrasound near TCA≈42 K suggest the evolution of spin canting from the matrix of long-range antiferromagnetic state.
TL;DR: In this article, the effect of phase transition on the electronic and vibrational spectra has been studied, which involves magnetic susceptibility, crystal structure, distortion of molecular shape, and charge ordering.
TL;DR: In this article, the effect of Mn site substitution of Al on the structural, magnetic and transport properties of charge ordered Pr{_0.5}Ca{_ 0.5]MnO{_3}.
Abstract: We report the effect of Mn site substitution of Al on the structural, magnetic and transport properties of charge ordered Pr{_0.5}Ca{_0.5}MnO{_3}. This substitution introduces impurities in the Mn-O-Mn network, causes the Mn{^3+}/Mn{^4+} ratio to deviate away from unity and is seen to predominantly replace Mn{^4+}. The strength of charge ordering is supressed with increasing Al doping, as is seen from ac susceptibility, the magnetocaloric effect and dc resistivity. The observation of traces of charge ordering over an extended range of impurity doping of 10% besides being indicative of the robust nature of charge ordering in Pr{_0.5}Ca{_0.5}MnO{_3}, also underscores the relatively insignificant effect that Al substitution has on the lattice distortions and the importance of non-magnetic substitutions. For all the samples, the conductivity in the temperature range above the charge ordering transition is observed to be due to the adiabatic hopping of small polarons, whereas below the charge ordering transition, Mott's variable range hopping mechanism is seen to be valid.
TL;DR: In this article, polarized Raman scattering of single crystals of Nd1−xSrxMnO3 (x = 0.3, 0.5Sr0.5) was reported.
Abstract: We report on polarized Raman scattering of single crystals of Nd1−xSrxMnO3 (x = 0.3, 0.5). Raman spectra of Nd0.7Sr0.3MnO3 show a significant change through the metal–insulator transition. In the ferromagnetic metallic phase phonon modes grow in intensity and number while the electronic continuum becomes more pronounced. We suggest that these effects are due to the strong competition between the localization and the delocalization of carriers which is the origin of the largest colossal magnetoresistance effect ever reported for the manganites. Raman spectra of Nd0.5Sr0.5MnO3, upon cooling through the charge-ordering temperature TCO = 148 K, exhibit several new lines which undergo a substantial hardening. This hardening is interpreted as a freezing of the Jahn–Teller distortions with a gradual decrease of a fraction of the ferromagnetic phase in the CE-type charge/orbital ordered state.