Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Q29: Focus Session: Ordering in Complex Oxides |
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Sponsoring Units: DMP GMAG Chair: Jaime Fernandez-Baca, Oak Ridge National Laboratory Room: 333 |
Wednesday, March 18, 2009 11:15AM - 11:51AM |
Q29.00001: Orbitals, reduced dimensionality and spin gaps in correlated oxides Invited Speaker: Due to directional character of orbitals very often orbital ordering leads to an effective dimensionality reduction. Especially strong are these effects in systems with triply-degenerate t$_{2g}$ electrons. One of the striking consequences thereof is the possibility to form spin-gap states instead of long-range magnetic ~ ordering. Such spin gap states may be formed on dimers, on trimers, on bigger clusters and even on chains. In the talk I will review this question, discuss different situations and different mechanisms of spin gap formation, and illustrate these general ideas on several examples (perovskite KCuF3; spinels MgTi2O4 and CuIr2S4 [1]; pyroxene NaTiSi2O6 [2]; layered systems La4Ru2O10 with square [3], LiVO2 with triangular [4], Li2RuO3 with honeycomb lattices [5], pyrochlore Tl2Ru2O7 [6]) \\[4pt] [1] D.I.Khomskii and T.Mizokawa, Phys.Rev.Lett. \textbf{94}, 156402 (2005); \\[0pt] [2] S.V.Streltsov, O.A.Popova and D.I.Khomskii, Phys. Rev. Lett. 96, 249701 (2006) \\[0pt] [3] Hua Wu et al., Phys.Rev.Lett. 96, 256402 (2006) \\[0pt] [4] H. Pen et al., Phys. Rev. Lett. 78, 1323 (1997) \\[0pt] [5] G.Jackeli and D.I.Khomskii, Phys. Rev. Lett. 100, 147203 (2008) \\[0pt] [6] Seongsu Lee et al., Nature Mater. 5, 471 (2006) [Preview Abstract] |
Wednesday, March 18, 2009 11:51AM - 12:03PM |
Q29.00002: Phase transitions and magnetostructural coupling in ZnCr$_2$O$_4$ from first principles Carl-Johan Eklund, Craig J. Fennie, Karin M. Rabe In the spinel structure oxide ZnCr$_2$O$_4$, a phase transition is observed from the high-temperature cubic phase to a low-temperature low-symmetry phase, reported as tetragonal$^1$ or orthorhombic$.^2~$ Building on a previous first-principles analysis of the zone-center phonons and spin-phonon coupling$,^3~$ we construct a first-principles effective Hamiltonian to investigate this transition. The local modes included are the Cr displacements, distortions of the Zn-centered tetrahedra, and the homogeneous strain. The magnetostructural coupling of these degrees of freedom to the spins of the Cr$^{3+}$ ions is included in the effective Hamiltonian parameterization and first-principles determination using a symmetry analysis. The role of the magnetostructural coupling in the phase transition will be analyzed and discussed. \\ 1. S. H. Lee et al., J. Phys. Cond. Matt. 19, 145259 (2007) \\ 2. V. N. Glazkov et al., http://arxiv.org/abs/0807.0546 \\ 3. C. J. Fennie and K. M. Rabe, Phys. Rev. Lett. 96, 205505 (2006) [Preview Abstract] |
Wednesday, March 18, 2009 12:03PM - 12:15PM |
Q29.00003: Charge-ordering in Magnetite studied by Magnetic Compton scattering B. Barbiellini, H. Kobayashi, M. Itou, S. Todo, P.E. Mijnarends, A. Bansil We present the [100]-[110] anisotropy of the magnetic Compton profile (MCP) in magnetite (Fe$_3$O$_4$). Good agreement is found between theory (within the local spin density approximation) and experiment with respect to the anisotropy in the metallic phase at 300K. However, the experimental curve for the insulating phase at 12K presents important changes at the low-momentum peak near 1 a.u. indicating that the bonding electrons are significantly affected by the Verwey transition. We will discuss whether these MCP anisotropy changes can be explained in terms of a charge-ordering mitigated by covalent effects [1]. Our study illustrates the high sensitivity of the Magnetic Compton scattering technique for extracting information on the electrons involved in the Verwey transition. Work supported in part by U.S. DOE. \\ \mbox{[1] M. Coey, Nature {\bf 430}, 155 (2004)} [Preview Abstract] |
Wednesday, March 18, 2009 12:15PM - 12:27PM |
Q29.00004: First-principles determined charge and orbital interactions in Fe$_3$O$_4$ Fei Zhou, Gerbrand Ceder In this work we have attempted to describe the charge and orbital degrees of freedom in fo with a classical effective energy model. Electronic and lattice effects are both included through first-principles calculated energies from which the model is parametrized. The calculated charge and orbital interactions in fo are found to be physically meaningful. The energy landscape is complex in terms of frustrated charge and orbital interactions as well as their competition. Additionally, although our predicted ground state structure has smaller periodicity than experimentally observed, it reveals the possibility that not only charge and orbital ordering, but the Jahn-Teller lattice distortions may also decide the structure. Therefore this work may help better understand the problem of the low-T magnetite structure. Beyond magnetite, our approach can be easily adapted to explore other transition metal oxides where charge and/or orbital order exist. [Preview Abstract] |
Wednesday, March 18, 2009 12:27PM - 12:39PM |
Q29.00005: Magnetic control of crystal chirality and gigantic magneto-chiral effect in CuB$_{2}$O$_{4}$ Mitsuru Saito, Kenta Ishikawa, Kouji Taniguchi, Taka-hisa Arima The possibility of a magnetic-field control of the chirality of matter has been debated since 19th century, because of its importance in the problem of homochirality. However, the difference of symmetry between magnetic fields and chirality implies that it would be impossible to induce chirality by a magnetic field alone. Here, we report the successful induction of crystal chirality in a noncentrosymmetric canted antiferromagnet, CuB$_{2}$O$_{4}$, by the application of a low-intensity static magnetic field[1]. The chirality is reversed by a 90-degree rotation of the direction of the magnetic field. This is the first successful magnetic control of chirality to the best of our knowledge. The induction of chirality by a magnetic field gives rise to a gigantic enhancement of magneto-chiral dichroism in this material. The magnitude of the effect is larger by three orders than the previous reports. The extraordinary enhancement allows us to design new magneto-optical devices. [1] M. Saito \textit{et al.,} Phys. Rev. Lett. \textbf{101 }117402 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 12:39PM - 12:51PM |
Q29.00006: Proposed Orbital Ordering in MnV$_2$O$_4$ from First-principles Calculations Tanusri Saha-Dasgupta, Soumyajit Sarkar, Tulika Maitra, Roser Valenti Based on density functional calculations, we propose a possible orbital ordering in MnV$_2$O$_4$ which consists of orbital chains running along crystallographic $a$ and $b$ directions with orbitals rotated alternatively by about 45$^{\circ}$ within each chain. We show that the consideration of correlation effects as implemented in the local spin density approximation (LSDA)+U approach is crucial for a correct description of the space group symmetry signifying a strong influence of the correlation-driven orbital ordering on the structural transitions in this system. Inclusion of spin-orbit effects does not seem to influence the orbital ordering pattern. We further find that the proposed orbital arrangement favors a non-collinear magnetic ordering of V spins, as observed experimentally. Exchange couplings among V spins are also calculated and discussed. [Preview Abstract] |
Wednesday, March 18, 2009 12:51PM - 1:03PM |
Q29.00007: Magnetic relaxation in TM$_{3}$V$_{2}$O$_{8}$ (TM = Cu, Ni, Co and Mn) staircase Kagome compounds Ambesh Dixit, C. Sudakar, N. Rogado, E. Morosan, R.J. Cava, A.P. Ramirez, Gavin Lawes The transition metal vanadate oxides having a staircase Kagome lattice structure exhibit rich magnetic phase diagrams, which arise from the complex geometry of these materials. Among these compounds, Ni$_{3}$V$_{2}$O$_{8}$ is particularly widely studied, as it develops simultaneous ferroelectric and incommensurate magnetic ordering at a single phase transition. In order to investigate the low frequency spin dynamics in these layered materials, we have probed the ac magnetic properties in these systems. We find that the Cu, Co, and Mn systems display strong magnetic relaxation in a spin ordered phase, with activation energies on the order of hundreds of Kelvin. We discuss these results in the context of spin-glass behaviour and domain wall motion. [Preview Abstract] |
Wednesday, March 18, 2009 1:03PM - 1:15PM |
Q29.00008: Effect of Zn doping on the phase transition temperatures of Ni$_{3}$V$_{2}$O$_{8}$ Akila Kumarasiri, Parashu Kharel, Ambesh Dixit, Gavin Lawes There is a considerable interest in understanding the nature of magnetic phase transition in geometrically frustrated materials. Ni$_{3}$V$_{2}$O$_{8}$ is one such system, with spin-1 Ni$^{2+}$ ions forming a layered buckled Kagome structure. We have studied the effects of doping spin-0 Zn ions on the magnetic phase transitions of powder Ni$_{3}$V$_{2}$O$_{8}$ using dielectric and heat capacity measurements. (Ni$_{1-x}$Zn$_{x})_{3}$V$_{2}$O$_{8}$ powder samples were synthesized starting with a mixture of Ni, V and Zn metal organic solutions mixed at appropriate atomic ratio. XRD and Raman studies show that (Ni$_{1-x}$Zn$_{x})_{3}$V$_{2}$O$_{8}$ powder samples annealed at 1000$^{\circ}$C crystallize in Ni$_{3}$V$_{2}$O$_{8}$ structure without forming any secondary phases. We have observed from heat capacity measurements that the phase transitions T$_{H}$, T$_{L,}$ and T$_{C}$ at 9.2K, 6.4K, and 3.9K expected for Ni$_{3}$V$_{2}$O$_{8}$ are present in our (Ni$_{1-x}$Zn$_{x})_{3}$V$_{2}$O$_{8}$ samples up to a Zn concentration of 20{\%}. The transition at 2.4 K was not clearly observed. All three transitions shift toward lower temperatures with an increase in Zn concentration. We will present the experimental results on the strong suppression of both T$_{H}$ and T$_{L}$ due to dilution of Ni$_{3}$V$_{2}$O$_{8}$ with non-magnetic Zn. Furthermore, we will present a quantitative comparison of this suppression with the 2D Ising and Heisenberg models. [Preview Abstract] |
Wednesday, March 18, 2009 1:15PM - 1:27PM |
Q29.00009: Electrical control of direction of orbital stripes in charge-orbital ordered state of single-layered manganite La$_{1/2}$Sr$_{3/2}$MnO$_{4}$ Shota Konno, Kouji Taniguchi, Hajime Sagayama, Taka-Hisa Arima Electrical control of the localized electron such as an electric-field induced metal-insulator transition in charge-orbital ordered (COO) state of perovskite-related manganese oxides has been intensively studied, since the large electroresistance effect in Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ was reported[1]. Moreover, the formation of orbital stripes in the COO state gives rise to in-plane anisotropies in the electrical, magnetic, and optical properties. However, there are few reports on controlling anisotropic properties in the COO state. We report an electric-field effect on the in-plane anisotropy in the COO state of a layered manganite La$_{1/2}$Sr$_{3/2}$MnO$_{4}$. After applying an electric field, a 90-degree rotation of COO states has been observed by using a polarizing microscope. A drastic change of the volumes of two COO domains was confirmed by means of synchrotron X-ray diffraction. [1]A. Asamitsu \textit{et al}., Nature \textbf{388}, 50(1997). [Preview Abstract] |
Wednesday, March 18, 2009 1:27PM - 1:39PM |
Q29.00010: Intersite charge transfer in the $A$-site-ordered LaCu$_{3}$Fe$_{4}$O$_{12}$ perovskite Youwen Long, Naoaki Hayashi, Takashi Saito, Masaki Azuma, Shigetoshi Muranaka, Yuichi Shimakawa A novel transition metal oxide LaCu$_{3}$Fe$_{4}$O$_{12}$ was prepared at 10 GPa and 1400 K. It crystallizes an $A$-site-ordered perovskite structure, which has a general chemical formula A$^{\prime}$A$_{3}$B$_{4}$O$_{12}$, with space group \textit{Im}-3. Bond valence sum calculations and M\"{o}ssbauer spectra confirm the change of charge combination at 393 K from a high-temperature La$^{3+}$Cu$^{2+}_{3}$Fe$^{3.75+}_{4}$O$_{12}$ with unusually high oxidation Fe$^{3.75+}$ ions at the $B$ site to a low-temperature La$^{3+}$Cu$^{3+}_{3}$Fe$^{3+}_{4}$O$_{12}$ with exceptional Cu$^{3+}$ ions at the $A$ site. The results strongly suggest an unusual intermetallic charge transfer between the $A$-site Cu and $B$-site Fe ions. The simultaneous valence change (3Cu$^{2+}$-3$e^{-}\to $3Cu$^{3+}$ and 4Fe$^{3.75+}$+3$e^{-}\to $4Fe$^{3+})$ caused by the $A-B$-site charge transfer leads to a first-order and reversible isostructural phase transition accompanied by an anomalous volume contraction as large as 1.0{\%}. Meanwhile, a paramagnetic metal to antiferromagnetic insulator transition is also induced by the $A-B$-site charge transfer. [Preview Abstract] |
Wednesday, March 18, 2009 1:39PM - 1:51PM |
Q29.00011: $A$-site Magnetism in Perovskites CaCu$_{3}B_{4}$O$_{12}$ ($B$ = Ge, Ti, Sn). Takashi Saito, Hiroshi Shiraki, Yuichi Shimakawa, Masaichiro Mizumaki $A$-site-ordered perovskites CaCu$_{3}$Ge$_{4}$O$_{12}$ and CaCu$_{3}$Sn$_{4}$O$_{12}$, both isostructural to antiferromagnetic CaCu$_{3}$Ti$_{4}$O$_{12}$, were found to be ferromagnets, which are very rare in cuprates. All of these materials may be called ``$A$-site magnets'', since they contain magnetic species only at the $A$-site of the perovskite \textit{AB}O$_{3}$ structure. The ferromagnetism of CaCu$_{3}B_{4}$O$_{12}$ ($B$ = Ge, Sn) is attributed to the ferromagnetic direct exchange interaction, whereas antiferromagnetic superexchange interaction, due to the Cu(3$d)$-O(2$p)$-Ti-(3$d)$ orbital hybridization, is dominant in antiferromagnetic CaCu$_{3}$Ti$_{4}$O$_{12}$. The $A$-site magnetism is controlled by the electronic structure of the non-magnetic $B$ site. Solid solutions CaCu$_{3}$(Ge,Ti)$_{4}$O$_{12}$ and CaCu$_{3}$(Ti,Sn)$_{4}$O$_{12}$ display phase boundary between ferromagnetic and antiferromagnetic phases. [1] H. Shiraki, T. Saito, Y. Shimakawa et al., \textit{Phys. Rev. B}, \textbf{76}, (2007) 140403. [2] Y. Shimakawa, H. Shiraki and T. Saito, \textit{J. Phys. Soc. Jpn.}, \textbf{77}, (2008) 113702. [Preview Abstract] |
Wednesday, March 18, 2009 1:51PM - 2:03PM |
Q29.00012: Structure and properties of high-oxygen-pressure annealed Sr$_{1-x}$La$_{x}$Co$_{0.5}$Fe$_{0.5}$O$_{3-d}$ (0$\le $x$\le $0.5) S. Remsen, K. Swierczek, B. Dabrowski, L. Suescun, S. Kolesnik Synthesis, oxygen content, structural, magnetic, and resistive properties will be discussed for the Sr$_{1-x}$La$_{x}$Co$_{0.5}$Fe$_{0.5}$O$_{3-d}$ perovskites. The x=0 sample shows oxygen-vacancy ordered Sr$_{8}$Co$_{4}$Fe$_{4}$O$_{23}$ tetragonal I4/mmm structure. With an increase of the La content the materials became oxygen stoichiometric and a lowering of the crystal symmetry is observed from cubic Pm3m (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). All samples show ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2. Conductivity is enhanced and small negative magneto-resistance is observed below T$_{C}$. Transport measurements up to 1100$^{o}$C show high conductivity that is affected by the varying oxygen content. 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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