Anisotropic optical spectra of doped manganites with pseudocubic perovskite structure

Tobe, K.; Kimura, T.; Tokura, Y.

doi:10.1103/physrevb.69.014407

Cited by 56 publications

(51 citation statements)

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“…This difference can produce the energy gain of the AP -OO arrangement. It should be stressed that a uniquely defined crystallographic axis, as is demonstrated here, is of great importance for the study of macroscopic anisotropic properties and can be rarely achieved in bulk single crystals [19]. The stacking structure of the orbital ordering may also be affected by the distortion of the A-site ions through the hybridization of A-site ions and oxygens [20].…”

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confidence: 99%

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

et al. 2006

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We performed resonant and nonresonant x-ray diffraction studies of a Nd0.5Sr0.5MnO3 thin film that exhibits a clear first-order transition. Lattice parameters vary drastically at the metal-insulator transition at 170 K (= T MI ), and superlattice reflections appear below 140 K (= T CO ). The electronic structure between T MI and T CO is identified as A-type antiferromagnetic with the d x 2 −y 2 ferroorbital ordering. Below T CO , a new type of antiferroorbital ordering emerges. The accommodation of the large lattice distortion at the first-order phase transition and the appearance of the novel orbital ordering are brought about by the anisotropy in the substrate, a new parameter for the phase control.Charge ordering and orbital ordering (CO/OO) are the characteristic phenomena, which render the complex electronic phase behavior to the strongly correlated electron systems, manganites in particular [1]. A number of theoretical and experimental studies on CO/OO in RE 1−x AE x MnO 3 (RE: rare earth metals; AE: alkali earth metals) have been conducted in the vicinity of x = 0.5 in order to understand the mechanism of the ordering and the resulting electronic properties [2]. Only three types of OO have been found dominant -one type of antiferroorbital structure (staggered arrangement of d 3x 2 −r 2 and d 3y 2 −r 2 orbitals, CE-OO) corresponding to CE-type antiferromagnetism (AF ) and two types of ferroorbital structures (d 3z 2 −r 2 and d x 2 −y 2 ) corresponding to C-type and A-type AF , respectively.The orbital order couples intimately to the lattice distortion. One can easily envision that a tetragonal lattice distortion promotes ferroorbital structures; the compressive strain within the c-plane favors d 3z 2 −r 2 (C-OO), while the tensile strain favors d x 2 −y 2 (A-OO). In fact, the phase control of ferroorbital ordering was achieved by manipulating the tetragonal lattice parameters employing a thin-film technique fabricated on (001) substrates [3]. In contrast, the antiferroorbital ordering * Present address: Correlated Electron Research Center (CERC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8562, Japan inevitably involves the in-plane anisotropy and no effective means for its control has been available thus far.Thin manganite films on (011) substrates [4] were recently found to exhibit a variety of clear first-order phase transitions [5,6], which has not been possible in those on (001) substrates that studied extensively [7,8,9,10]. From the transport and magnetic properties of these films, the antiferroorbital order has been anticipated in them, although the direct evidence of the OO as well as the knowledge of the OO structures in these films, which affect the magnetic and/or electronic properties, were lacking. In this Letter, we present results of synchrotron x-ray diffraction measurements on a Nd 0.5 Sr 0.5 MnO 3 thin film grown on SrTiO 3 (011). A novel antiferroorbital structure has been identified. We clearly demonstrate a new handle to manipulate th...

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Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

et al. 2006

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“…Since the opticalregion charge dynamics as measured by SW can be strongly anisotropic in the charge/orbital-ordered states depending on their ordering patterns, ⌬SW nor can give a good insight into the electronic order of the insulating state. 16 As shown in Fig. 3͑b͒, ⌬SW nor for 0.04Ͻ y Ͻ 0.14 is much larger than in the other regions.…”

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“…Such a spectral feature for the charge-gap transition is typical of one-dimensional electronic system. 16,22 Tetragonal symmetry with the longest a-axis lattice parameter ͓Fig. 3͑d͔͒ suggests the anisotropic crystal field acting on the Mn site.…”

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Competing electronic orders in anisotropically strained(Pr0.6Ca0.4)1−<

Lee

Nakamura²,

Okuyama³

et al. 2010

Phys. Rev. B

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We have explored the competing phases in the anisotropically strained manganese oxide with use of a composition-spread thin film where two contrastive ground states, i.e., ferromagnetic metal and charge/orbitalordered insulator, are designed to compete with a continuous variation in the chemical composition. Taking advantage of a systematic inspection of the phase evolutions, we have confirmed that competing electronic orders could be realized in thin-film form. In particular, we found a possibly one-dimensional orbital-ordered insulating state near the metal-insulator phase boundary which can be disturbed by a relatively low magnetic field.Competing orders and resultant phase instabilities in electronic states of a solid are of great importance for exploiting gigantic or sensitive responses against external stimuli. Realization of such functions has been made with use of thin films and/or junctions with the tuned phase competition and the stable homogeneity in electronic response over tens of nanometer to micron size. Transition-metal oxides with correlated electrons are promising hosts of such functionalities; e.g., insulator-metal or superconducting transition and magnetic transitions induced by electric/magnetic-field stimulation, light irradiation, heat, stress, etc. Compared to bulk materials, however, the phase competition in their thin-film form can be severely suppressed by the epitaxial strain from the substrate. For instance, when transition-metal oxides with simple cubic perovskite symmetry are grown on the ͑001͒ surface of the substrate as shown in Fig. 1͑a͒, biaxial stress usually overwhelms other instabilities and makes the film inactive against additional stimuli. As an effort to minimize such strain effects, the films with a large thickness are grown to make the strain fully relaxed or vicinal substrates are sometimes used to release the accumulated elastic energy at the step edges. 1 The state-of-the-art thin-film technology provides us with another possibility to overcome this problem by exploiting the ͑011͒ orientation of the substrate as shown in Fig. 1͑b͒. 2 In this case, only one axis is directly clamped to the substrate and hence the film gains more freedom so as to behave like a strain-free material. Recently, the charge/ orbital-ordered state for some manganite thin films was realized by this method as in corresponding bulk materials, 2-4 which lowered the barrier in the thin-film technology of correlated-electron system toward its actual application targeting a wider range of bulk properties.Here, we address the issue of phase competition in the thin-film system by investigating the anisotropically strained manganese oxide, ͑Pr 0.6 Ca 0.4 ͒ 1−y ͑La 0.6 Sr 0.4 ͒ y MnO 3 . La 0.6 Sr 0.4 MnO 3 and Pr 0.6 Ca 0.4 MnO 3 are the typical and contrastive systems, where the ferromagnetic metallic and charge/ orbital-ordered insulating ground states are formed, respectively. Furthermore, a size mismatch of constituent ions is comparatively small between La and Sr as well as between Pr and Ca, whic...

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“…4,5) In particular, the orbital degree of freedom strongly affects the magnetic interaction 6) and anisotropy of electronic conductivity. 7) In RVO 3 (R: rare earth or Y), the two valence electrons of V 3þ ions occupy the near-triply degenerate t 2g orbitals, and orbital and spin degrees of freedom exist. Hence, RVO 3 shows various physical properties owing to its orbital and spin states.…”

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confidence: 99%

Magnetic Phase Diagrams of YVO₃ and TbVO₃ under High Pressure

et al. 2012

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Magnetic states in RVO 3 (R = Y, Tb) were investigated using low-temperature and high-pressure neutrondiffraction techniques, and the pressure-temperature magnetic phase diagrams were clarified up to 6.2 GPa. We elucidated that, on application of pressure, the magnetic ground state changes from C-type spin ordering (C-SO) to G-type spin ordering (G-SO); this corresponds to the orbital ground-state switching from G-type orbital ordering (G-OO) to C-type orbital ordering (C-OO). It is also interesting that the G-SO transition occurs simultaneously with the C-OO transition, but not with the G-OO one. When the transition temperature of C-OO exceeds that of G-OO under high pressure, the G-OO phase vanishes completely, and a simultaneous spin and orbital order-disorder phase transition occurs. Such a transition is the first case in perovskite-type transition-metal oxides.

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Anisotropic optical spectra of doped manganites with pseudocubic perovskite structure

Cited by 56 publications

References 50 publications

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

Competing electronic orders in anisotropically strained(Pr0.6Ca0.4)1−<

Magnetic Phase Diagrams of YVO₃ and TbVO₃ under High Pressure

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Anisotropic optical spectra of doped manganites with pseudocubic perovskite structure

Cited by 56 publications

References 50 publications

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

Novel Orbital Ordering Induced by Anisotropic Stress in a Manganite Thin Film

Competing electronic orders in anisotropically strained(Pr0.6Ca0.4)1−<

Magnetic Phase Diagrams of YVO3 and TbVO3 under High Pressure

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Magnetic Phase Diagrams of YVO₃ and TbVO₃ under High Pressure