Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q17: Focus Session: Bulk Properties of Complex Oxides - Ruthenates |
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Sponsoring Units: DMP GMAG Chair: Ward Plummer, Louisiana State University Room: D174 |
Wednesday, March 23, 2011 11:15AM - 11:51AM |
Q17.00001: High-pressure Synthesis and Magnetic Properties of 4d and 5d Transition-metal Oxides Invited Speaker: The pressure effect on synthesis of oxides with perovskite ABO$_{3}$ and perovskite-related structures has become more clear in recent years. The geometric tolerance factor t $\equiv $ (A-O)/$\surd $2(B-O) measures the structural stability. High-pressure synthesis enlarges the range of the t factor where the perovskite structure can be stabilized. For the ABO$_{3}$ compounds with t $>$ 1, high pressure reduces the t factor since the A-O bond is more compressible than the B-O bond. Therefore, perovskite would be the high-pressure phase for ambient-pressure polytype structures. However, the bonding compressibility argument is no longer valid for the ABO$_{3}$ with t $<$ 1. A dt/dP $>$ 0 is normally obtained for t less than but very close to 1$, i.e.$ the orthorhombic distortion becomes smaller under pressure. For those highly distorted perovskites with t factor far less than one, pressure enlarges further the orthorhombic distortion and eventually leads to a phase transition to the post-perovskite phase. As for PbRuO$_{3}$, high pressure prefers the small-volume perovskite phase relative to a competitive pyrochlore phase Pb$_{2}$Ru$_{2}$O$_{7}$. Understanding the pressure effect and the new capacity provided by a Walker-type multianvil press enabled us to expand the perovskite family and to obtain new phases of 4d and 5d oxides. Studies of these new 4d and 5d oxides allow us not only to address long-standing problems, but also to explore exotic physical properties. (1) In the perovskite ARuO$_{3}$ (A= alkaline earth), we have completed the phase diagram from A= Ca to Sr and to Ba and also accounted for the A-cation size-variance effect. A systematic study of the Curie temperature T$_{c}$ and the critical behavior as a function of the average A-site size and the size variance as well as external high pressures reveals explicitly the crucial role of the lattice strain on the ferromagnetism. The mean-field critical behaviour near T$_{c}$ found previously in SrRuO$_{3}$ is not typical of these perovskite ruthenates. T$_{c}$ is completely suppressed by Pb doping in Sr$_{1-x}$Pb$_{x}$RuO$_{3}$ not due to the steric effect, but to the orbital hybridization between Pb$^{2+}$ 6s and Ru$^{4+}$ 4d. As the end member, metallic PbRuO$_{3}$ undergoes a first-order phase transition to a metallic \textit{Imma} phase at T$_{t} \approx $ 90 K. (2) A new polytype phase 5H has been synthesized under a narrow pressure range, which fits the structural sequence along with other polytypes 9R, 6H and 3C of BaIrO$_{3}$. The ground states of these BaIrO$_{3}$ polytypes evolve from a ferromagnetic insulator with T$_{c }\approx $ 180 K in the 9R phase to a ferromagnetic metal with T$_{c }\approx $ 50 K in the 5H phase, and finally to an exchange-enhanced paramagnetic metal in the 6H phase, which may be close to a quantum critical point. (3) In the Ca$_{1-x}$Sr$_{x}$IrO$_{3}$ system, high pressure stabilizes the post-perovskite structure on the Ca side (x $<$ 0.3), but favors the perovskite structure on the Sr side (x $>$ 0.6). Refs. J.-G. Cheng, \textit{et al.} PRB \textbf{80}, 104430(2009); \textbf{80}, 174426 (2009); \textbf{81}, 134412(2010); JACS \textbf{131}, 7461(2009). [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q17.00002: Spectroscopic Imaging - Scanning Tunneling Microscopy studies of the Nematic Metamagnet Sr$_3$Ru$_2$O$_7$ M.P. Allan, T.-M. Chuang, Y. Xie, A.W. Rost, R.S. Perry, J.-F. Mercure, A. Gibbs, A.P. Mackenzie, J.C. Davis The metamagnetic perovskite Sr$_3$Ru$_2$O$_7$ can be tuned towards a putative quantum critical point in an external magnetic field, and in ultrapure samples, an electronic nematic forms in a small region of the phase diagram around this putative quantum critical point. Much insight about these phenomena in Sr$_3$Ru$_2$O$_7$ come from a wealth of high-quality thermodynamic experiments but little is known about the microscopic electronic origin of criticality and nematicity. We recently re-engineered our SI-STM to achieve sub-Kelvin temperatures and magnetic fields up to 9T, and are now imaging the local density of states in different regions of the Sr$_3$Ru$_2$O$_7$ phase diagram, including within the nematic phase. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q17.00003: Entropy Accumulation near Itinerant Magnetic Quantum Critical Points Jianda Wu, Lijun Zhu, Qimiao Si, Andreas Rost, Andy Mackenzie Quantum critical point (QCP) occurs at a continuous phase transition at zero temperature. It follows from general hyperscaling argument that, near a QCP, the Gr\"uneisen ratio (ratio of thermal expansion coefficient to specific heat) diverges and entropy accumulates [1]. The enhanced entropy has been observed near the field-induced metamagnetic QCP in Sr3Ru2O7[2]. Here we present a detailed theoretical study of entropy across itinerant-magnetic QCPs, with a focus on the ferromagnetic cases. We propose a regularization scheme for the effect of a dangerously irrelevant quartic coupling on the free energy [3], and calculate the entropy using this scheme. While the entropy accumulation near the QCP basically follows the hyperscaling arguments, the correction to scaling is sizeable especially for the two-dimensional case. We compare the theoretical results with the experimental data for Sr3Ru2O7 [2], providing an entropic characterization of the degree to which the metamagnetic QCP in this system is described by the itinerant-magnetic quantum criticality. \\[4pt] [1] L. Zhu et al, PRL 91, 066404 (2003).\\[0pt] [2] A.W. Rost et al, Science 325, 1360 (2009).\\[0pt] [3] J. Wu, L. Zhu, and Q. Si, arXiv:1010.4593, to appear in J. Phys.: Conf. Series. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q17.00004: Thermodynamics of the critical fluctuations and nematic phase formation of Sr$_3$Ru$_2$O$_7$ Andreas W. Rost, Robin S. Perry, Jean-Francois Mercure, Santiago A. Grigera, Andrew P. Mackenzie The itinerant metamagnet Sr$_3$Ru$_2$O$_7$ has motivated a wide range of experimental and theoretical work in recent years because of the discovery of an unusual low temperature phase which is forming in the vicinity of a proposed quantum critical point. The transport properties of this phase which exhibit strong electron-nematic-like behaviour [1] have led to a range of theoretical proposals for the underlying physics [2]. A major challenge both experimentally and theoretically is the investigation of the thermodynamic properties of both this unusual phase and the fluctuations associated with the quantum critical point. Here I will report on recent thermodynamic measurements. I will concentrate on new specific heat measurements investigating the nature of the critical fluctuations of the system as well as the low energy excitations of the novel phase. \\[4pt] [1] R.A. Borzi, S.A. Grigera, J. Farrell, R.S. Perry, S. Lister, S.L. Lee, D.A. Tennant, Y. Maeno \& A.P. Mackenzie, Science 315, 214 (2007). \newline [2] For a recent review, see E. Fradkin, S. A. Kivelson, M. J. Lawler, J. P. Eisenstein \& A. P. Mackenzie, Annual Review of Condensed Matter Physics 1, 153 (2010) [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q17.00005: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q17.00006: Magnetic and structural transitions tuned by non-magnetic Ti doping in Ca3Ru2O7 Jin Peng, Gaochao Wang, Leonard Spinu, Xianglin Ke, Tao Hong, Zhiqiang Mao We report the effect of Ti doping on the structural and magnetic transitions in the bilayer Ruthenate Ca3Ru2O7. Ca3Ru2O7 orders antiferromagnetically at 56 K followed by a simultaneous structural and metal-insulator transition at 48 K [1]. Ti doping in Ca3Ru2O7 causes dramatic changes in both antiferromagnetic and structural transitions. With the Ti doping concentration above 5\%, both transitions move to much higher temperature and merge, e.g. TN~85 K for 5\% Ti, 113 K for 10\% Ti. For the latter sample, the structural parameters change much more remarkably through the transition compared to Ca3Ru2O7 [2]. Such structural and magnetic transitions tuned by Ti-doping highlight the strong spin-lattice coupling in Ca3Ru2O7. Neutron scattering measurement on these samples will also be discussed. \\[4pt] [1] Cao G et al; PRB 78, 1751 (1997)\\[0pt] [2] Yoshida Y et al; PRB 72, 054412 (2005) [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q17.00007: Element-resolved electronic and magnetic properties of Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ V.B. Nascimento, J.W. Freeland, Biao Hu, R. Jin, E.W. Plummer Bulk Sr$_{3}$Ru$_{2}$O$_{7}$ is a metal with short-range antiferromagnetic correlation developed at low temperatures. In the Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ series, the partial substitution of Ru by Mn changes both electronic and magnetic correlations driven by the modification of lattice degree of freedom. We have employed polarized x-rays to perform an element-resolved study of electronic and magnetic properties of this system with 0 $<$ x $\le $ 0.5. Our results indicate that at low doping Mn goes in as an electron acceptor (i.e. Mn 3+) which effectively dopes holes into the Ru system in a systematic way with increasing x. Using x-ray magnetic circular dichroism we have extracted the Mn and Ru contributions to the total magnetic moment, which will be connected to measurements of the total moment. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q17.00008: Metastable Magnetic states in Ca$_{3}$Ru$_{2}$O$_{7}$ D. Fobes, J. Peng, Z.Q. Mao We have performed systematic in-plane angle dependent c-axis transverse magnetotransport measurements on the double layered ruthenate Ca$_{3}$Ru$_{2}$O$_{7}$ throughout a broad field and temperature range. Our results reveal the magnetic states for $H\|b$ to be significantly more complex than for $H\|a$. When magnetic field is applied along the b-axis we probe several metastable magnetic states in close proximity to phase boundaries of long-range ordered antiferromagnetic (AFM) states previously revealed by neutron scattering, i.e. AFM states with magnetic moments oriented along the b-axis (AFM-b) and a-axis (AFM-a); canted AFM state (CAFM) (Wei Bao \textit{et al.}, Phys. Rev. Lett. \textbf{100}, 247203 (2006)). These metastable states are characterized by magnetoresistivity anisotropy distinct from that seen in the AFM-a, AFM-b, or CAFM phases, and switch either to a weakly ferromagnetic or AFM-b state when the magnetic field is rotated toward the \textit{a}-axis. Additionally, our results highlight the complex nature of the spin-charge coupling in Ca$_{3}$Ru$_{2}$O$_{7}$. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q17.00009: Interplay of oxygen octahedral rotations and electronic instabilities in strontium ruthenate Ruddlesden-Poppers from first principles Johannes Voss, Craig J. Fennie The Ruddlesden-Popper ruthenates Sr$_{n+1}$Ru$_n$O$_{3n+1}$ display a broad range of electronic phases including $p$-wave superconductivity, electronic nematicity, and ferromagnetism. Elucidating the role of the number of perovskite blocks, $n$, in the realization of these differently ordered electronic states remains a challenge. Additionally dramatic experimental advances now enable the atomic scale growth of these complex oxide thin films on a variety of substrates coherently, allowing for the application of tunable epitaxial strain and subsequently the ability to control structural distortions such as oxygen octahedral rotations. Here we investigate from first principles the effect of oxygen octahedral rotations on the electronic structure of Sr$_2$RuO$_4$ and Sr$_3$Ru$_2$O$_7$. We discuss possible implications for the physics of the bulk systems and point towards new effects in thin films. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q17.00010: Ca$_{2}$Ru$_{1-x}$Cr$_{x}$O$_{4 }$(0 $<$ x $<$ 0.13): Negative volume thermal expansion via orbital and magnetic orders T.F. Qi, O.B. Korneta, M. Ge, L.E. De Long, G. Cao, S. Parkin, P. Schlottmann Ca$_{2}$RuO$_{4}$ undergoes a metal-insulator transition at T$_{MI}$= 357 K, followed by a well-separated transition to antiferromagnetic order at T$_{N }$= 110 K. Dilute Cr doping for Ru reduces the temperature of the orthorhombic distortion at T$_{MI}$ and induces ferromagnetic behavior at T$_{C}$. The lattice volume V of Ca$_{2}$Ru$_{1-x}$Cr$_{x}$O$_{4}$ (0 $<$ x $<$ 0.13) abruptly expands with cooling at both T$_{MI}$ and T$_{C}$, giving rise to a total volume expansion $\Delta $V/V $\approx $ 1 {\%}, which sharply contrasts the smooth temperature dependence of the few known examples of negative volume thermal expansion driven by anharmonic phonon modes. In addition, the near absence of volume thermal expansion between T$_{C}$ and T$_{MI}$ represents an Invar effect. The two phase transitions, which surprisingly mimic the classic freezing transition of water, suggest an exotic ground state driven by an extraordinary coupling between spin, orbit and lattice degrees of freedom. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q17.00011: Correlation between Structural and Magnetic Properties in Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ Single Crystals Biao Hu, Gregory T. McCandless, O.V. Garlea, S. Stadler, E.W. Plummer, R. Jin We have studied the Mn-doping (x) dependence of structural and magnetic properties in Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7 }$. The system remains tetragonal as determined by single-crystal X-ray diffraction with the lattice parameters $a$ and $c$ varying with x. Correspondingly, the value of Jahn-Teller distortion ($\Delta _{JT})$ of (Ru,Mn)O$_{6}$ octahedron decreases with increasing x with $\Delta _{JT }$= 1.0 for x$\sim $0.5. At the same doping level, we note the sign change of Curie-Weiss temperature $\Theta _{CW}$ derived from high-temperature magnetic susceptibility. The correlation between structural and magnetic properties will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q17.00012: Managing magnetization and antiferromagnetic coupling in epitaxially grown magnetic oxide heterostructures of (Ga,Fe)2O3 and SrRuO3 Jihye Lee, William Jo, Christian Meny , Francois Roulland, Nathalie Viart We have grown b-axis oriented epitaxial (Ga,Fe)2O3 (GFO) thin films on (111) oriented SrRuO3 (SRO) by pulsed laser deposition to know spin interaction in multilayer system. The easy axis of magnetization of the GFO is located on the plane of the thin films. On the other hand, SRO has unique anisotropic properties on various crystallographic directions in their structure. Magnetic properties of the films were measured as a function of temperature and external magnetic field by a superconducting quantum interference magnetometer. Curie temperature of SRO and GFO was measured at 150K and 370K, respectively. According to the direction of external magnetic field, the magnetic moment value of the GFO/SRO heterostructures show different behavior due to antiferromagnetic coupling. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q17.00013: ARPES Studies of the Evolution of the Ruthenate Family with Dimensionality John Harter, Dawei Shen, Carolina Adamo, Charles Brooks, Daniel Shai, Eric Monkman, Darrell Schlom, Kyle Shen The Ruddlesden-Popper homologous series of ruthenates exhibits a wide range of remarkable electronic phenomena coupled to dimensionality, from spin-triplet superconductivity in quasi-two-dimensional single-layer Sr$_{2}$RuO$_{4}$, to metamagnetism and nematicity in bilayer Sr$_{3}$Ru$_{2}$O$_{7}$, to ferromagnetism in the fully three-dimensional pseudocubic end-member SrRuO$_{3}$. We report high resolution angle-resolved photoemission spectroscopy measurements of the electronic structure of ruthenate films grown by molecular beam epitaxy, with particular interest in the evolution of the quasiparticle interactions with increasing dimensionality. We start by investigating the anisotropic renormalization of quasiparticles in SrRuO$_{3}$ by strong electron-boson coupling, and examine changes in the Fermi surface and associated quasiparticles as a function of temperature through the Fermi-liquid to non-Fermi-liquid crossover and above the ferromagnetic Curie temperature. We also investigate the strain dependence of the low-energy electronic structure and quasiparticle interactions of Sr$_{3}$Ru$_{2}$O$_{7}$. [Preview Abstract] |
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