Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P29: Focus Session: Manganites |
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Sponsoring Units: DMP GMAG Chair: Gang Cao, University of Kentucky Room: 333 |
Wednesday, March 18, 2009 8:00AM - 8:36AM |
P29.00001: Recent studies of models for manganites in the bulk and in superlattices Invited Speaker: In this talk, we will review our recent double-exchange model studies for manganites and some related experimental discoveries. First, we will briefly address the existence of a clear CMR effect in numerical simulations, and the short-range spin and charge correlations and local density of states in this CMR regime [1,2]. Second, we will analyze manganite superlattices (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$. The reconstruction of charge density, spin order, and orbital order at the interfaces and the relation with a novel experimentally observed metal-insulator transition (MIT) at $n=3$ will be discussed [3]. Finally, the multiferroic spiral spin order in the undoped manganite $R$MnO$_3$ ($R$=Tb, Dy) will also be briefly studied under the double-exchange framework [4]. \\[4pt] [1] R. Yu, S. Dong, C. \c{S}en, G. Alvarez, and E. Dagotto. Phys. Rev. B 77, 214434 (2008).\\[0pt] [2] C. \c{S}en, G. Alvarez, and E. Dagotto, Phys. Rev. Lett. 98, 127202 (2007).\\[0pt] [3] S. Dong, R. Yu, S. Yunoki, G. Alvarez, J.-M. Liu, and E. Dagotto, Phys. Rev. B 78, in press(R) (2008).\\[0pt] [4] S. Dong, R. Yu, S. Yunoki, J.-M. Liu, and E. Dagotto, Phys. Rev. B 78, 155121 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P29.00002: Small dissimilarity in lattice distortion triggers anomalously large anisotropic magnetoresistance in manganite perovskite. R. Li, H. Wang, X.Z. Wang, Y. Matsui, X. Wang, Z. Cheng, B. Shen, E.W. Plummer, Jiandi Zhang Anisotropic magnetoresistance (AMR) effects are of fundamental importance not only for providing information on spin-orbital coupling and magneto-crystalline anisotropy, but also for enabling technological applications. Here, we report an anomalous AMR effect in a prototype manganite single crystal---La$_{0.69}$Ca$_{0.31}$MnO$_{3}$. We demonstrate that the broken symmetry, through cubic to orthorhombic structural distortion in the crystal, leads to profound anisotropic magneto-transport behavior. The measured AMR behavior shows a direct correlation with the anisotropic field-tuned metal-insulator transition (MIT) in the system and can be understood via a phenomenological uniaxial anisotropy model. It is revealed that a small crystalline anisotropy can trigger a large AMR near the MIT phase boundary of the system. [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P29.00003: Doping dependent evolution of the polaron metal N. Mannella, K. Tanaka, S.-K. Mo, W. Yang, H. Zheng, J. Mitchell, J. Zaanen, T.P. Deveraux, N. Nagaosa, Z. Hussain, Z.-X. Shen Experimental and theoretical evidence has already suggested that the ferromagnetic metallic (FM) phase in colossal magnetoresistive manganites is not a conventional metal but rather a polaronic conductor. In the bilayer manganites La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (LSMO), Angle Resolved Photoemission (ARPES) experiment revealed that the FM phase is a polaronic metal with a strong anisotropic character of the electronic excitations [1,2]. A small but well-defined quasiparticle (QP) with heavy mass along the [110] or ``nodal'' direction is found to account for the metallic properties and their temperature dependent evolution [2]. In this talk, we will discuss recent ARPES results on the x = 0.60 composition and contrast them to the x = 0.40 results. Recent work has shown that the region in proximity of x = 0.60 constitute the most metallic bilayer manganite with DC conductivity about one order of magnitude higher than that corresponding to the region 0.30 $<$ x $<$ 0.40. Much as in the x = 0.40 composition, for x = 0.60 along the nodal direction we observe a peak-dip-hump structure with QP of heavy effective mass. Quantitative differences in the electron-phonon coupling constant $\lambda $, the QP spectral weight and the hump energy are fully consistent with the doping evolution of the transport properties. [1] Nature \underline {438}, 474 (2005), [2] Phys. Rev. B \underline {76}, 233102 (2007). [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P29.00004: Metal-insulator transition in La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x=0.59) revealed by ARPES Zhe Sun, J. F. Douglas, Q. Wang, A. Fedorov, Y. -D. Chuang, H. Zheng, J. F. Mitchell, D. S. Dessau Using angle-resolved photoemission spectroscopy (ARPES), we studied the metal-insulator transition of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ (x=0.59). Below T$_{C}$, there is significant metallic weight at the Fermi level, while a gap opens above T$_{C}$, in excellent agreement with resistivity measurements. We also found that in this compound the metal-insulator transition is associated with a remarkable coherent-incoherent weight transfer from the dispersive band to a non-dispersive feature over a large energy scale. The band dispersion also shows an unusual change with increasing temperature, suggesting complicated interactions in this material. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P29.00005: Role of Oxygen Electrons in the Metal-Insulator Transition in the Mangnetoresistive Oxide La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ W. Al-Sawai, B. Barbiellini, A. Koizumi, P.E. Mijnarends, T. Nagao, K. Hirota, M. Itou, Y. Sakurai, A. Bansil We have studied the [100]-[110] anisotropy of the Compton profile in the bilayer manganite. Quantitative agreement is found between theory and experiment with respect to the anisotropy in the two metallic phases (i.e. the low temperature ferromagnetic and the colossal magnetoresistant phase under a magnetic field of 7T). Robust signatures of the metal-insulator transition are identified in the momentum density for the paramagnetic phase above the Curie temperature. We interpret our results as providing direct evidence for the transition from the metallic-like to the admixed ionic-covalent bonding accompanying the magnetic transition. The number of electrons involved in this phase transition is estimated from the area enclosed by the Compton profile anisotropy differences. Our study demonstrates the sensitivity of the Compton scattering technique for identifying the number and type of electrons involved in the metal-insulator transition. Work supported in part by the USDOE. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P29.00006: Charge/Orbital Ordered Phases of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7-\delta }$ Kenneth Gray, Hong Zheng, Qing'An Li, John Mitchell Our studies have significantly modified the conventionally-held view of the phase diagram of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7-\delta }$ for two compositions exhibiting charge (and orbital) order (CO), i.e., at hole doping levels, h=x-$\delta $, of $\sim $0.5 and $\sim $0.6. These CO states are stable over very narrow doping ranges ($\Delta $h$\sim \pm $0.005) at the lowest temperatures, but those ranges increase at higher temperatures (to $\Delta $h$\sim \pm $0.02) in a manner consistent with simple entropy considerations. Such narrow ranges dictate the crucial need for crystal homogeneity. Attesting to such homogeneity is a conductivity ratio of $>$10$^{10}$ upon crossing the first-order phase boundary from CO at h=0.60 to AAFM at h$\sim $0.59 or h$\sim $0.61 plus two findings that were missed in the existing literature: that these CO phases are the ground state at the lowest temperatures and, for h$\sim $0.5, that coexistence of the CO and AAFM phase is absent at any temperature. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P29.00007: Resonant Inelastic X-ray Scattering in CE-ordered bilayer manganite Frank Weber, Stephan Rosenkranz, John-Paul Castellan, John Mitchell, Hong Zheng, Diego Casa, Thomas Gog Resonant Inelastic X-ray Scattering (RIXS) has recently emerged as valuable tool in the study of orbital excitations in transition metal oxides.Stepah We have performed RIXS measurements at the Mn K-edge in the half doped bilayer manganite LaSr$_{2}$Mn$_{2}$O$_{7}$. Our sample was a non-reentrant single crystal with long range CE order down to lowest temperatures. We made wave vector dependent energy loss scans with $\Delta $E$\le $15eV in the (110) direction at three different temperatures, i.e. T=75K (AFM CE ordered), 175K (PM CE ordered) and 250K (PM and no orbital order). In particular, we compare the temperature dependence of the 2eV peak with previous results on manganite perovskites [1]. Work supported by US DOE BES-DMS DE-AC02-06CH11357.\\[4pt] [1] S. Grenier et al. Phys. Rev. Lett. 94, 047203 (2005) [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P29.00008: Time-resolved Optical Study of Charge-ordered Manganites. Takahisa Tokumoto, Judy Cherian, Ryan deRosa, Paula Sahanggamu, Sanhita Ghosh, Stephen McGill, Tesfaye Gebre, Haidong Zhou, Christopher Wiebe We study the effects of applied electric fields and large magnetic fields on the optical properties of Pr$_{(1-x)}$Ca$_{x} $MnO$_{3}$ (x$\sim $0.5) (PCMO) and La$_{(1-x)}$Ca$_{x}$MnO$_{3} $ (x$\sim $0.18) (LCMO) using time-resolved techniques. Our measurements are performed down to 4 K and in dc magnetic fields up to 31 T. The conductivity of the low-temperature strong charge/orbital ordering in PCMO is altered by the application of an electric field and a magnetic field. We demonstrate that time- resolved optical reflection and Kerr effect measurements are capable of capturing these mixed electronic and magnetic effects to gain further insight into the change of the ordering. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P29.00009: Lattice-form dependent charge- and orbital- ordered states in perovskite-related mangananites Daisuke Okuyama, Yusuke Tokunaga, Reiji Kumai, Yasujiro Taguchi, Taka-hisa Arima, Yoshinori Tokura Charge and orbital order in half-doped manganites has been extensively studied since the magnetic-field induced melting of charge and orbital order (CO-OO) results in colossal magnetoresistance phenomena. However, there remain two points to be clarified, concerning the CO-OO states. First issue is the degree of charge disproportionation (CD); Full CD between Mn$^{3+}$ and Mn$^{4+}$ ions has been widely believed while charge density wave ordering with less distinct CD has also been recently proposed. Another issue is the orbital shape (OS) at Mn$^{3+}$ ion in the CO-OO phase. The reason why the OSs of (La,Ca)MnO$_3$ ((3y$^2$-r$^2$)/(3$x^2$-r$^2$)) and (La,Sr)$_2$MnO$_4$ ((y$^2$-z$^2$)/(z$^2$-x$^2$)) are different is not clarified. In our study, we tried to clarify the CDs and OSs in (Eu,Ca)$_2$MnO$_4$ and (Pr,Sr,Ca)$_3$Mn$_2$O$_7$ by means of x-ray crystal structural analyses and well established methods of bond valence sum and Kanamori diagram, and to compare with those of (Pr,Ca)MnO$_3$. We found that the CD of all the samples is much smaller than unity. In addition, the CDs and OSs are systematically dependent on the dimension of MnO$_6$ network. From simple consideration, we concluded that apical oxygens play an important role. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P29.00010: Charge and orbital order effects in La$_{x}$Sr$_{1-x}$MnO$_{2.6}$ B. Dabrowski, L. Suescun, S. Kolesnik, S. Remsen, J. Mais Low temperature annealing in hydrogen have been used to obtain oxygen vacancy ordered manganites Sr$_{4+n}$Mn$^{3+}_{4}$Mn$^{4+}_{n}$O$_{10+3n}$ (n=0, 1, 3) displaying charge and orbital ordering. For the La-substituted n=1 phase four Mn$^{3+}$ cations exhibit elongated pyramidal coordination while the fifth one in octahedral coordination shows decreasing formal valence Mn$^{(4- 5x)+}$. This selective doping produces structural strain resulting in unusual apically compressed coordination leading to complex magnetic interactions and frustration. Similar structures have been previously observed for the (La,Ba)CuO$_{3-d}$ cuprates revealing common vacancy ordering relationships in perovskites for which highly distorted Mn$^{3+}$ (Cu$^{2+})$ and symmetric Mn$^{4+}$ (Cu$^{3+})$ ions are present simultaneously. Work at NIU was supported by the NSF-DMR-0706610 and at ANL by the U.S. DOE under contract No. DE-AC02-06CH11357. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P29.00011: Phase separations in La$_{1-x}$Ca$_{x}$MnO$_{3}$ at critical doping levels J. Tao, Q. Jie, Q. Li, Y. Zhu, D. Niebieskikwiat, M.B. Salamon, S.J. Pennycook La$_{1-x}$Ca$_{x}$MnO$_{3}$ specimens have been widely studied for their rich and complex physics. There is a boundary in the phase diagram at $x$ = 0.50. At low temperatures, the system is ferromagnetic for $x$ less than 0.5 while charge ordering phase is favored for $x$ equal to or greater than 0.5. The mechanism for this drastic change over the continuous doping still remains unclear. Here we report our electron diffraction study on bulk La$_{1-x}$Ca$_{x}$MnO$_{3}$ at the critical doping $x$ = 0.48 and 0.50. Lorentz microscopy is also employed in the study to obtain the magnetic domain information during the phase transitions in these two specimens. The observed structure is integrated with the measured properties and it shows novel phenomena of the materials at nanoscale. This work is funded by U.S. DOE/BES under Contract No. DE-AC02-98CH10886. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P29.00012: High Pressure Neutron Diffraction Study on a Self-doped CMR Manganite Peng Gao, Trevor A. Tyson, Zhiqiang Chen, Chris Stock, Matthew G. Tucker High-pressure neutron diffraction measurements were conducted on the self-doped CMR material La$_{0.85}$MnO$_{3-\sigma }$ up to $\sim $ 7 GPa above and below the magnetic ordering temperatures. The diffraction data show no abrupt structure change (space group) in the whole pressure and temperature range studied. The detailed atomic structural changes are examined. In addition the magnetic structure as a function of pressure and temperature was explored at high and low pressures. Peaks that could be attributed to magnetic scattering appear at $\sim $230K under $\sim $ 0.7 GPa and persist at high pressure ($\sim $7GPa). The pressure dependent distortion of the MnO6 polyhedra is discussed. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P29.00013: Universal magnetic behavior the electron-doped SrMnO$_{3}$ cubic perovskite S. Kolesnik, B. Dabrowski, O. Chmaissem SrMnO$_{3}$ is the end member of a widely explored family of colossal magnetoresistive manganites R$_{x}$Sr$_{1-x}$MnO$_{3}$ (R=rare earth elements). Low-level R$^{3+}$ substitutions change the antiferromagnetic order from G-type in cubic SrMnO$_{3}$ to C-type in tetragonal R$_{x}$Sr$_{1-x}$MnO$_{3}$ through first-order resistive and structural transitions. From the magnetization, transport, and neutron diffraction experiments we observe that a similar change can be induced by B-site substitutions in SrMn$_{1-x}$M$_{x}$O$_{3}$ (M=Ru$^{5+}$,Mo$^{6+})$ both generating Mn$^{3+}$ in the Mn$^{4+}$ matrix. For both A-site and B-site substitutions, the N\'{e}el temperature is dependent on the Mn$^{3+}$ concentration in a universal way. These observations reveal that the magnetic and electronic properties of low-level substituted SrMnO$_{3}$ are controlled by the band filling throughout the increasing role of local distortions of Mn$^{3+}$O$_{6}$ octahedra changing from randomly diluted to cooperative character of the entire lattice. Work at NIU was supported by the NSF (DMR-0706610) and at ANL by the U.S. DOE under contract No. DE-AC02-06CH11357. [Preview Abstract] |
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