Optical evidence of mixed-phase behavior in manganite films

Gao, Peng; Tyson, Trevor; Liu, Z.; Deleon, M.; Dubourdieu, C.

doi:10.1103/physrevb.78.220404

Cited by 8 publications

(3 citation statements)

References 42 publications

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“…These materials reveal intrinsic inhomogeneities found in manganites as nanoscale granularity. 21,22 This might also be concomitant to cuprates where phase competition might be tied to oxygen vacancies distributed at random in the lattice inhomogeneous patterns reflecting disorder and distortion. Then, our results also aim to add a critical experimental view of the nature of metal-insulator transition in oxides as our results are from known samples made of components providing completely disordered environment.…”

Section: Electron Dynamics In Films Made Of Transition Metal Nanograimentioning

confidence: 99%

Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance

Massa

Denardin

Socolovsky

et al. 2009

Journal of Applied Physics

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We report on near normal infrared reflectivity spectra of ~550 nm thick films made of cosputtered transition metal nanograins and SiO 2 in a wide range of metal fractions. Co 0.85 (SiO 2 ) 0.15 ,with conductivity well above the percolation threshold has a frequency and temperature behavior according to what it is find in conducting metal oxides. The electron scattering rate displays an unique relaxation time characteristic of single type of carriers experiencing strong electron-phonon interactions. Using small polaron fits we individualize those phonons as glass vibrational modes. Ni 0.61 (SiO 2 ) 0.39 , with a metal fraction closer to the percolation threshold, undergoes a metal-non metal transition at ~77 K.Here, as it is suggested by the scattering rate nearly quadratic dependence, we identify two relaxation times (two carrier contributions) associated to a Drude mode and a mid-infrared overdamped band, respectively. Disorder induced, the mid-infrared contribution drives the phase transition by thermal electron localization. Co 0.51 (SiO 2 ) 0.49 has the reflectivity of an insulator with a distinctive band at ~1450cm −1 originating in electron promotion, localization, and defect induced polaron formation. Angle dependent oblique reflectivity of globally insulating Co 0.38 (SiO 2 ) 0.62 , Fe 0.34 (SiO 2 ) 0.66, and Ni 0.28 (SiO 2 ) 0.72 , reveals a remarkable resonance at that band threshold. We understand this as due to the excitation by normal to the film electric fields of defect localized electrons in the metallic nanoparticles. At higher oblique angles, this localized nanoplasma couples to SiO 2 longitudinal optical Berreman phonons resulting a band peak softening reminiscent to the phonon behavior undergoing strong electron-phonon interactions. Singular to a globally insulating phase, we believe that this resonance might be a useful tool for tracking metal-insulator phase transitions in inhomogeneous materials.

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Section: Electron Dynamics In Films Made Of Transition Metal Nanograimentioning

confidence: 99%

Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance

Massa

Denardin

Socolovsky

et al. 2009

Journal of Applied Physics

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“…The electronic structure of the manganites has a close relationship with their crystal structure, specially the distance between Mn and O atoms. [13][14][15][16] It is well known that the nanosized materials may exhibit unique electrical, magnetic, and optical properties far different from those of their bulk counterparts because of low dimensionality and quantum confinement effect. 17 In this work, we study the magnetic and optical properties of GdMnO 3 nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Magnetic and optical properties of multiferroic GdMnO3 nanoparticles

Wang

Cui

et al. 2010

Journal of Applied Physics

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The magnetic and optical properties of multiferroic GdMnO 3 nanoparticles synthesized by a polymerized complex method have been investigated. The GdMnO 3 nanoparticles crystallized in orthorhombic perovskite-type structure. The zero-field-cooled and field-cooled magnetizations show that complicated magnetic transitions occur in a temperature range from 2 to 60 K, which were confirmed by magnetic hysteresis loops. Three shoulder absorption peaks centered at about 2.0, 2.3, and 2.7 eV are attributed to the Mn ͑3d͒-electronic transitions, while an absorption peak at around 4.1 eV corresponds to the charge-transfer transitions between O ͑2p͒ and Mn ͑3d͒ states. UV emission at about 396 and 406 nm and blue emission at around 466 nm have been found, which may be attributed to the spin-allowed charge-transfer transitions.

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“…When the thickness is decreased, interface (substrate/film) may change competing instabilities and favour insulating regions (due to a reduction of carriers at the interface) such that the film becomes insulating and eventually no more ferromagnetic. We recently evidenced by synchrotron infrared measurements such a mixed-phase behaviour in La 0.8 MnO 3-δ , films (thickness of 120 nm and 410 nm) grown on LaAlO 3 substrate [86]. Infrared reflectivity spectra were acquired over the range 100-8000 cm -1 and in the temperature range of 10-304 K. While the metal/insulator transition temperature T MI and the magnetic ordering temperature T c are close (∼295 K), we showed that the onset of the free carrier density occurs at a significantly lower temperature (∼45 K below), as shown in Figure 3(c).…”

Section: Colossal Magnetoresistive Oxidesmentioning

confidence: 94%

Oxides heterostructures for nanoelectronics

Dubourdieu

Gélard

Salicio

et al. 2010

IJNT

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We summarise in this paper the work of two groups focusing on the synthesis and characterisation of functional oxide for nanoelectronic applications. In the first section, we discuss the growth by liquid-injection MOCVD of oxides heterostructures. Interface engineering for the minimisation of silicate formation during the growth of polycrystalline SrTiO 3 on Si is first presented. It is realised via the change of reactant flow or chemical nature at the Si surface. We then report on the epitaxy on oxide substrates of manganites films and superlattices and on their magnetic and electrical properties. La 0.7 Sr 0.3 MnO 3 and La 0.8 MnO 3-δ as well as multiferroic hexagonal ReMnO 3 manganites are considered. We show that the film thickness and related strain may be used to tune the properties. Finally, we demonstrate the growth of MgO nanowires by CVD at a moderate temperature of 600°C, using gold as a catalyst. In the second section, we discuss the growth of epitaxial oxide heterostructures by MBE. First, the direct epitaxy of SrTiO 3 on Si is considered. Issues and control of the SrTiO 3 /Si interface are discussed. An abrupt interface is achieved. We show that SrTiO 3 on Si can be used as a buffer layer for the epitaxy of various perovskite oxides such as LaAlO 3 or La 0.7 Sr 0.3 MnO 3 . La 0.7 Sr 0.3 MnO 3 films are ferromagnetic and metallic at room temperature. The epitaxial growth of complex oxides on Si wafers opens up the route to the integration of a wide variety of functionalities in nanoelectronics. Finally, we discuss the monolithic integration of III-V compounds such as InP on Si using epitaxial SrTiO 3 buffer layers for the future integration of optics on Si.

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Optical evidence of mixed-phase behavior in manganite films

Cited by 8 publications

References 42 publications

Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance

Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance

Magnetic and optical properties of multiferroic GdMnO3 nanoparticles

Oxides heterostructures for nanoelectronics

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