4PO8-70 Spin Glass Behavior in Perovskite-Like (La_0.7Pb_0.3)(Mn_1-xCo_x)O₃ System

Ming-Fong Tai 1, Ting Sheng Huang 1, and J.B. Shi 2. 1 Deparment of Physics, National Chung Cheng University, 160 San Hsing, Ming-Hsiung, Chia-yi 621, Taiwan. 2 Department of Electronic Engineering, Feng Chia University, Taichung 402, Taiwan.

Presenting Author: M.-F. Tai

The perovskite-like (La_0.7Pb_0.3)(Mn_1-xCo_x)O₃ series with x = 0 -1.0 were prepared using a standard solid state reaction method. The as-prepared samples were characterized by X-ray powder diffraction patterns and were found to be of single phase of an rhombohedral structure. Spin glass behaivor is observed in all samples except the pure manganites (x = 0) by using ac/dc magnetic measurements. Structural and magnetic properties are investigated in detail. The results are compared with those of barium doping system.

4PO8-71 Atomic and magnetic structure of (La_1-yPr_y)_0.7Ca_0.3MnO₃: A-cation size

A.M. Balagurov 1, V.L. Aksenov 1, N.A. Babushkina 2, O.Yu. Gorbenko 3, P. Fischer 4, A.R. Kaul 3, V.Yu. Pomjakushin 1, and D.V. Sheptyakov 1. 1 Frank Laboratory of Neutron Physics JINR, 141980 Dubna, Russia. 2 RRC "Kurchatov" Institute, 123182 Moscow, Russia. 3 Chemistry Department, Moscow State University, 119899 Moscow, Russia. 4 Laboratory of Neutron Scattering, ETH Zurich and PSI, CH-5232 Villigen PSI, Switzerland.

Presenting Author: A.M. Balagurov

A series of (La_1-yPr_y)_0.7Ca_0.3MnO₃ samples with y=0.5, 0.6, 0.7 and 0.75 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition with y=0.75 the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes (99.7% ¹⁶O, metallic and ferromagnetic at T_FM £ 110 K), and the other one enriched by ¹⁸Î in 75% (insulating in the whole temperature range and with collinear antiferromagnetic order at TAFM £ 150 K). These two samples have been found identical in crystal and magnetic structure down to transition of the sample with ¹⁶O into the metallic ferromagnetic phase. It means that their quite different transport and magnetic properties at T £ 110 K are driven by the different oxygen atoms dynamics solely.

The synchronism in temperature behaviour of the intensities of the AFM and CO diffraction peaks indicate in favour of phase segregation of the samples on AFM-insulating and FM-metallic phases. The conclusion was also confirmed by experiment in external magnetic field. This experiment with (La_0.25Pr_0.75)_0.7Ca_0.3MnO₃ revealed the presence of two critical field values: 0.1 T for starting of saturation FM diffraction peak intensities and 1 T for starting of AFM peak intensities fast decrease.

4PO8-72 Tailoring of Epitaxial Strain in Doped Lanthanummanganite Thin Films

Hanns-Ulrich Habermeier, Fereidoon Razavi, Rainer Praus, and Gudrun M. Gross, MPI für Festkörperforschung Heisenbergstr. 1, D -70569 Stuttgart, Germany

Presenting Author: H.-U. Habermeier

We have grown single crystalline doped LaMnO₃ thin films using the pulsed laser deposition technique and analysed the interrelation of epitaxial strain and growth-induced defects with transport and optical properties. An unexpected possibiliy of tailoring the metal-insulator transition temperature has been developed and correlated with microscopic structural features. Due to their unique magnetotransport properties thin films of perovskite-type doped LaMnO₃ have attracted much scientific and technological interest. Based on the pulsed laser deposition technique we have developed an in-situ deposition process to prepare single phase, epitaxially grown thin films of the system La_1-xCa_xMnO₃ using SrTiO₃ single crystal substrates. Depending on the deposition temperature we can adjust the metal-insulator transition temperature x = 0.33 between 150K and 270K. The films were analyzed with respect to their structural [X- Ray diffraction, cross-sectional TEM], optical [Raman Spectroscopy] as well as magnetic field and pressure dependent transport properties. For optimum deposition conditions the microstructure is characterized by a pseudomorphic film growth for thicknesses up to 50 nm followed by a columnar epitaxial microstructure.

Raman lines recorded in various scattering configurations and temperatures were assigned to definite oxygen related vibrational modes, thus opening the possibility to study structural details, locally. In comparison to other perovskite-type thin films such as epitaxially grown YBa₂Cu₃O₇ the Raman lines are much broader, indicating an enhanced structural instability of the perovskite manganites. Furthermore, Raman spectroscopy offers the possibility to analyse the epitaxial strain, quantitatively.

In addition to the well known magnetic field induced reduction of resistivity and shift of T_c to higher temperatures, hydrostatic pressure in zero magnetic field causes similar effects. A hydrostatic pressure reduces the resistivity at the ferromagnetic ordering temperature for films doped with 33% Ca at a rate of dr /dp = 150 W/GPa and a shift of T_c to higher values by dT_c/dp =+27 K/Pa. The results are discussed in the light of growth-induced epitaxial strain and microstructural features of the films as well.

4PO8-73 Whisker crystal growth in the system La-Ba-Mn-O

Eugene Goodilin 1, Ekaterina Pomerantseva 2, Valery Petrykin 3, Alexander Knot’ko 1, Oleg Gorbenko 1, Nikolay N. Oleynikov 1, Yury D.Tretyakov 1, and M. Kakihana 3. 1 Department of Chemistry, Moscow State University, Moscow 119899, Russia. 2 Higher School of Materials Science, Moscow State University. 3 Materials and Structures Lab., Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama 226-8503, Japan.

Presenting Author: Y.D. Tretyakov

A growth technique was developed to produce 0.1-1 mm long whisker crystals in the system La-Ba-Mn-O using BaCl₂-KCl fluxes. The volume fraction of antiferromagnetic whiskers varied from 10 to about 50% among globular ferromagnetic particles of the usual (La,Ba)MnO₃ manganite. It was found by EDX that the needle crystals contain excess of Mn, a smaller variable amount of Ba and negligible amount of La with no considerable impurities of K or Cl (Mn:(Ba, La)= 7:1 - 3:1). Lattice constants calculated from SAED and powder XRD patterns allowed to assume that the crystals have to be assigned to a new phase with a rhombohedral lattice (a=14.10 A, a = 58.10° ). The presence of both Ba-containing compounds and KCl was observed to be a necessary condition for the needles formation. It was supposed that the needles are formed via molten KCl evaporation and the transport of constituents through a vapor phase to growing tips of the whiskers (Vapor-Liquid-Crystal mechanism).

4PO8-74 The electronic structure of cuprate chains, ladders and planes from high energy spectroscopy.

J. Fink, C. Duerr, S. Legner, R. Neudert, A. Koitzsch, Z. Hu, S.V. Borisenko, M. Knupfer, and M.S. Golden, IFW Dresden, Institute for Solid State Research, P.O. Box 270016, D-01171 Dresden, Germany

Presenting Author: M.S. Golden

We present experimental investigations of the character, symmetry and dynamics of charge carriers in model cuprate systems containing Cu-O chains, ladders and planes. Firstly, the orbital location and symmetry of the hole states have been probed using polarisation-dependent x-ray absorption spectroscopy. ARPES data then shed light on the dispersion relation of single holes in these systems, and are complemented by information regarding the dynamics of holes extracted from the screening behaviour observed in high resolution XPS studies. Finally, momentum-dependent electron energy-loss spectroscopy delivers information on the dynamics of charge transfer excitations.

These results illustrate the defining role played by the dimensionality and spin background on the electronic excitations in this class of materials. In addition, the dataset as a whole provides a demanding test-track for models developed to describe the electronic structure of low dimensional cuprate systems.

We are grateful to: H. Eisaki, S. Uchida, S. Haffner, N. Nuecker, S. Schuppler, G. Kaindl, K. Penc, W. Stephan, S.-L. Drechsler, H. Rosner, R. Hayn for providing samples and experimental or theoretical support.

Thanks for financial support to: BMBF (05SB8 BDA6) DFG (Fi439/7-1, Graduiertenkolleg 'Struktur- und Korrelationseffekte in Festkoerpern').

4PO8-75 In Situ Study of the Formation and Decomposition Processes of Infinite-Layer Cuprates

Emilio Morán 1, Javier Garcia-Jaca 1, Xavier Turrillas 2, Simon M. Clark 3, and Miguel.Á. Alario-Franco 1. 1 Laboratorio de Química del Estado Sólido, Facultad de Ciencias Químicas, Universidad Complutense, E-28040 Madrid, Spain (EU). 2 Dpto. Química Física. IETcc. CSIC. C/ Serrano Galvache s/n E-28033 Madrid, Spain (EU). 3 CLRC Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD, United Kingdom (EU).

Presenting Author: E. Moran

The formation and decomposition processes of the Ca_0.5Sr_0.5CuO₂ high-pressure phase with infinite-layer structure is followed in-situ by energy dispersive X-ray diffraction using a synchrotron radiation source. The different phases present in the precursor sample (Sr₁₄Cu₂₄O₄₁, Ca₂CuO₃ and CaO) show an unlike reactivity during the high-pressure synthesis. The Ca₂CuO₃ is much more reactive than the ladder compound and, hence, initially the high-pressure phase formed is richer in calcium than in strontium as is deduced from the calculated lattice parameters. During this step the most significant changes are observed in the alkaline-earth layer and are evidenced by the variation of the c lattice parameter during the formation process. The decomposition reaction of the infinite-layer phase is produced at 1200 ºC to yield a mixture of phases including the n=1 member of the Sr_n-1Cu_nO_2n-1 family and (Ca,Sr)₂CuO₃ as is confirmed by electron diffraction techniques. This reaction implies a volume reduction observed as fast shift of the infinite-layer phase related peaks. In this second reaction, the most significant changes are observed in the a-b plane, implying that the CuO₂ planes are partially condensed.

4PO8-76 Momentum-resolved correlated charge excitations in high T_c parent cuprate Ca₂CuO₂Cl₂ - A Resonant Inelastic X-ray Scattering Study

M.Z. Hasan 1, E.D. Isaacs 2, Z.X. Shen 1, L.L. Miller 3, K. Tsutsui 4, T. Tohyama 4, and S. Maekawa 4. 1 Dept.of Appl.Phys. & SSRL-SLAC, Stanford University, Ca 94305. 2 Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974. 3 Dept.of Physcis, Iowa State University, Ames, IA 50011. 4 Inst.of Materials Res., Tohoku Univ., Sendai 9808577, Japan.

Presenting Author: M.Z. Hasan

We report a momentum-resolved study of correlated charge excitations in parent high T_c cuprate antiferromagnetic insulator Ca₂CuO₂Cl₂ using inelastic x-ray scattering at the Cu K-edge. The excitation spectrum shows two features - a nondispersive feature around 5.5 eV reported earlier and another dispersive feature around 2.5 eV. The lower energy feature disperses upward about 1 eV for Q along (0,0) to (p ,p ) whereas it does not disperse in going from (0,0) to (p /2,0) then disperses again upward by about 0.4 eV. This is the first clear observation of large dispersion across the Mott-gap measured in the bulk crystal using Resonant Inelastic X-ray Scattering (RIXS) in a high T_c parent cuprate. Earlier Angle-Resolved Photoemission (ARPES) results have shown the existence of a high-energy d-wave like dispersion of the occupied states in this insulator [1]. We used RIXS [2] to probe the full symmetry of the Mott(charge-transfer type) gap. By combining our ARPES and recent RIXS results we determine the nature of nonlocal charged excitations across the Mott gap in cuprates.

We also demonstrate the relevance and power of such momentum-resolved (relatively new type of ) spectroscopic studies in providing powerful insights into formulating an effective hamiltonian for the high T_c parent compounds specially the importance of INTERSITE Coulomb coupling in understanding the fundamental electronic structure of parent cuprates [3].

[1] F.Ronning et. al., Science, V-282, 2067, 1998 (Stanford ARPES Group).

[2] P.Abbamonte et. al., PRL, V-83, 860, 1999 (Bell-Labs IXS Group) and others.

[3] K.Tsutsui et. al., cond-mat/9905372, 26 May 1999 (IMR-Japan Theory Group).

4PO8-77 Physical Property of Solid Solution Containing of Metallic and Insulating Vanadium Oxides

Kazuo Sakai, Shiro Mizuno, Hironaru Murakami, and Toshimichi Ito, Dept. of Electrical Eng., Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan

Presenting Author: K. Sakai

Recently much attention has directed to the strongly electron correlation system since the discovery of high-T_c superconductor. We take also interest in the AVO_3-x-BVO_3-x (Atri-valent ion, B=di-valent ion) system, especially Y_1-xSr_xVO_3-x or Y_1-xCa_xVO_3-x. This system is a solid solution between SrVO_3-x or CaVO_3-x as a metal and YVO_3-x as an insulator, the valence of which vanadium ion varies with the oxygen content.

YVO_3-x itself shows very curious magnetic property, which has been already reported in detail. [1] The solid solution in the Y_1-xSr_xVO_3-x system was limited to x=0.3. The energy gap in the region lower than x=0.3 is rapidly reduced with the increase of Sr molar fraction to be 66meV in x=0.1 and 5meV in x=0.2. The anomalous magnetic behavior shown in the YVO_3-x under the field cooling process was reduced. Whereas, the electric properties in the Y_1-xCa_xVO_3-x system are entirely different. The energy gaps in x<0.5 were scarcely changed, while the electric properties in x=0.7 and 0.9 displayed a metallic behavior down to ~200 K, finally transferred to a semiconducting one in the temperature region lower than ~200K. At present the reproducibility of these results is checked with the magnetic measurement, expanding to the farther compositional region.

[1] K. Sakai et al., Physica C, 317-318,(1999) 464.

4PO8-78 Phase-relations study of Sr-Mo-O system for new superconductors search

Naoki Shirakawa and Shin-ichi Ikeda, Physical Science Div., Electrotechnical Laboratory, Tsukuba 305-8568 Japan

Presenting Author: N. Shirakawa

The recent upsurge of interest in the ruthenate superconductor Sr₂RuO₄ has stimulated us to investigate molybdates with Mo⁴⁺ ions in MoO₆ octahedra. There Mo⁴⁺ is expected to have two 4d-electrons in the t2g bands with three-fold degeneracy in contrast to two 4d-holes for Ru⁴⁺. Both SrMoO₃ (113) and Sr₂MoO₄ (214) had been reported in Sr-Mo-O system as in the case of Sr-Ru-O. We presumed that such perovskite-related structures would provide a more suitable stage for superconductivity than other structures like the pyrochlore would. We therefore started to study 113 and 214 as candidates for new superconductors.

Some authors had encountered difficulty in the synthesis of 214 [1]. We confirmed, however, its existence by exploring the ternary phase diagram of Sr-Mo-O at various temperatures. Although we looked for the condition to synthesize single-phased 214, only the mixture of 214, 113, and Mo metal has been obtained so far. We are working on the synthesis of single-phase samples in order to elucidate whether 214 is a superconductor.

Since there may be unreported compounds that become superconducting in this ternary system, we are also carrying out search for such compounds, by varying atmospheres and temperature.

[1] G.J. McCarthy et al., J. inorg. nucl. Chem. 35, 2669 (1973).

4PO8-79 Magnetic and Transport Properties of Perovskite-related Strontium Molybdates

Shin-ichi Ikeda and Naoki Shirakawa, Physical Science Div., Electrotechnical Laboratory, Tsukuba 305-8568, Japan

Presenting Author: S. Ikeda

Spin-triplet superconductivity in the layered perovskite Sr₂RuO₄ has been an intriguing issue on strong electron correlations in layered perovskite oxides (LPO) with 4d-transition metals[1]. Except for the ruthenates, magnetic and transport properties of 4d-LPO have not been studied completely due to few syntheses and characterizations. A candidate compound for a new superconductor is Sr₂MoO₄ among 4d-LPO, because Sr₂MoO₄ is expected to have an equivalent configuration of 4d-electrons (S=1) to that of Sr₂RuO₄ in addition to having the same crystal structure with I4/mmm symmetry.

In order to find a new superconducting phase, we have tried to synthesize a strontium molybdate SrMoO₃ as well as Sr₂MoO₄ by means of a conventional solid-state reaction method. Polycrystalline SrMoO₃ without any impurity phases has been obtained. It shows somewhat enhanced Pauli-paramagnetic susceptibility between 2K and 300K. The value after diamagnetic correction is about 2.3x10^-4 emu/Mo mol, consistent with the value reported previously [2]. This makes a sharp contrast to the itinerant ferromagnetism (T_c=160 K) in the ruthenate counterpart SrRuO₃. On the other hand, we are able to obtain multi-phase samples of Sr₂MoO₄, SrMoO₃ and Mo in the synthesis of Sr₂MoO₄ for the present. Further investigations of synthetic conditions are in progress. We will discuss the difference in electronic structures between strontium molybdates and strontium ruthenates also using the data of electrical resistivity.

[1] K. Ishida et al., Nature 396 (1998) 658.

[2] G.H. Bouchard and M.J. Sienko, Inorganic Chemistry 7 (1968) 441.