Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B17: Focus Session: Bulk Properties of Complex Oxides - Manganites II |
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Sponsoring Units: GMAG DMP Chair: Gang Cao, University of Kentucky Room: D174 |
Monday, March 21, 2011 11:15AM - 11:51AM |
B17.00001: Dynamics of bi-stripes and a colossal metal-insulator transition in the bi-layer manganite La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ $(x\sim0.59)$ Invited Speaker: Electronic phases with stripe patterns have been intensively investigated for their vital roles in novel properties of correlated electronic materials. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. By studying the electronic structure of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ $(x\sim0.59)$ and in combination with earlier scattering measurements, we demonstrate the variation of electronic properties accompanying the melting of so-called bi-stripes in this material. The static bi-stripes can strongly localize the electrons in the insulating phase above $T_c\sim160$K, while mobile electrons grow up and coexist with a significant portion of localized electrons when the static bi-stripes melt below $T_c$. The presence of localized electrons below $T_c$ suggests that the melting bi-stripes exist as a fluctuating counterpart. From static to melting, the bi-stripes lead to a ``colossal'' metal-insulator transition in this material. Work was done in collaboration with Q. Wang, A. V. Fedorov, H. Zheng, J. F. Mitchell, D. S. Dessau. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B17.00002: Probing multiple magnetic transitions and phase coexistence in mixed phase manganites M.H. Phan, N.S. Bingham, H. Srikanth, C.L. Zhang, S.W. Cheong La$_{5/8-y}$Pr$_{y}$Ca$_{3/8}$MnO$_{3 }$(LPCMO) manganites exhibit a complex phase diagram due to coexisting and competing magnetic and electronic phases. A complete understanding of the origin of phase coexistence and separation in this system has remained elusive. To resolve this, it is essential to employ experimental methods that allow detailed investigations of the temperature and magnetic field response of the different phases. In this study we introduce magnetocaloric effect (MCE) and radio-frequency transverse susceptibility (TS) experiments as being ideally suited for this purpose. While MCE is generally considered in the community as an ``applied'' measurement tool to characterize magnetic refrigerant materials, we demonstrate that it is actually a very useful probe of magnetic transitions and ground state magnetic properties in LPCMO. TS experiments probe a phase conversion between the charge-ordered and ferromagnetic phases and magnetic field-induced kinetic arrest. Our studies provide an important understanding of the phase coexistence and separation in mixed phase systems like LPCMO. [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B17.00003: Soft x-ray investigation on the spin and orbital states of La$_{1.4}$Sr$_{1.6}$Mn$_2$O$_7$ K.-T. Ko, H. Jang, J.-H. Park, B.-G. Park, J.-Y. Kim, Sung Baek Kim, S-W. Cheong The spin and orbital states of La$_{1.4}$Sr$_{1.6}$Mn$_2$O$_7$ was investigated by using the x-ray absorption spectroscopy (XAS) and the soft x-ray resonant scattering (SXRS) at Mn $L_ {2,3}$-edge. The field induced spin reorientation transition was observed by SXRS. The polarization dependent analysis revealed that the AFM spin axis changes from out-of-plane to in-plane axis. Additionally, the orbital states were determined from the polarization dependent XAS and CI model calculation, where the orbital state were changed by cooling temperature and external magnetic field. Here, the orbital states of low temperature ferromagnetic and field induced ferromagnetic are identical. Finally, we discuss the magnetoelastic coupling including spin and orbital structure of La$_{1.4}$Sr$_{1.6}$Mn$_2$O$_7$. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:27PM |
B17.00004: Optical Investigation on Collective Dynamics of Charge-Orbital Density Wave in Layered Manganites Jun Fujioka, Yoshiaki Ida, Youtarou Takahashi, Noriaki Kida, Ryo Shimano, Yoshinori Tokura We have investigated the broad band optical spectra on the layered manganites $R_{1-x}$Sr$_{1+x}$MnO$_4$ (R=Nd and La) to reveal the collective charge/orbital density wave dynamics by means of the terahertz time domain spectroscopy [1]. The collective charge/orbital density wave excitation is observed around 9 meV in the charge/orbital stripe phase, when the nominal $e_g$-electron filling (1-$x$) of Mn-ion is less than around 1/3. By contrast, such a collective mode almost vanishes at $x$=1/2, which is explained in terms of the enhanced Jahn-Teller interaction cooperative with the electron correlation effect. \\[4pt] [1] J. Fujioka {\it et al.}, Phys. Rev. B. {\bf 82}, 140409(R) (2010). [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B17.00005: Bilayer manganites: polarons in the midst of a metallic breakdown Mark Golden, Freek Massee, Sanne de Jong, Yingkai Huang, Andrew Boothroyd, D. Prabhakaran, Rolf Follath, Andrei Varykhalov, Luc Patthey, Ming Shi, Jeroen Goedkoop The exact nature of the low temperature electronic phase of the manganite materials family, and hence the origin of their colossal magnetoresistive (CMR) transition is still a flagship issue in emergent correlated matter research. By combining new photoemission and tunneling data, we show that in the bilayer ($N$=2) manganite La$_{\mathrm{2-2x}}$Sr$_{\mathrm{1+2x}}$Mn$_2$O$_7$ the lattice/spin/orbital polaronic degrees of freedom win out, all across the CMR region of the phase diagram. This means that the generic ground state is that of a system in which strong interactions result in vanishing coherent quasi--particle spectral weight at the Fermi level for all locations in $k$--space. The incoherence of the charge carriers offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopic data. The stacking number $N$ is the key factor for true metallic behavior, as an intergrowth-driven breakdown of the polaronic domination to give a robust metal possessing a traditional Fermi surface is seen in the bilayer system. [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B17.00006: Synthesis, Structure, and Physical Properties of Ba$_{2}$Mn$_{2}$Sb$_{2}$O Single Crystals Jianneng Li, S. Stadler, A. Karki, Y. Xiong, R. Jin We have grown high-quality single crystals of Ba$_{2}$Mn$_{2}$Sb$_{2}$O, which possesses the hexagonal structure as determined by X-ray powder diffraction technique. The magnetic susceptibility ($\chi )$ is isotropic above T$_{N }\sim $ 60 K, initially increasing with increasing temperature (T). After reaching the maximum at T$_{MAX} \quad \sim $ 150 K, $\chi $ decreases with increasing T and can be described by Curie-Weiss law with negative Curie-Weiss temperature. Below T$_{N}$, magnetic anisotropy is observed: $\chi _{ab}$ decreases sharply but $\chi _{c}$ increases with decreasing T, suggesting an antiferromagnetic type ordering at T$_{N}$. Interestingly, the temperature dependence of electrical resistivity along both \textit{ab} plane and $c$ direction changes from exponential dependence above T$_{MAX}$ to logarithmic dependence below T$_{MAX}$, reflecting strong Kondo effect. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B17.00007: Evaluating Born and local effective charges in nanoscale MnO Q.-C. Sun, X.S. Xu, S.N. Baker, A.D. Christianson, J.L. Musfeldt Phonons are exquisitely sensitive to finite length scale effects in complex materials because they are intimately connected to charge, polarizability, and structure, and a quantitative analysis of their behavior can reveal microscopic aspects of chemical bonding. To investigate these effects in a model correlated oxide, we measured the infrared vibrational properties of 8 nm particles of MnO, compared the results with the analogous bulk material, and quantified the phonon confinement with a calculation of Born effective charge. Our analysis reveals that the Born effective charge decreases by $\sim$20\% compared to the bulk material. This finding is important for understanding finite length scale effects in this simple binary oxide and the more complicated functional oxides that emanate from this parent compound. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B17.00008: Collective Phase Mode and the Role of lattice distortions at T$_{N}\sim $T$_{C}$ in XMn$_{2}$O$_{5}$ (X= Bi, Pr, Sm, Gd, Tb) N.E. Massa, A.F. Garc\'Ia Flores, E. Granado, G.F.L. Fabbris, G. de M. Azevedo, L. del Campo, D. De Sousa Meneses, P. Echegut, M.J. Mart\'Inez-Lope, J.A. Alonso We report on detailed temperature dependent infrared reflectivity, Raman, local structure, and X-ray diffraction measurements of multiferroic XMn$_{2}$O$_{5}$ (X= Bi, Pr, Sm, Gd, Tb). While for BiMn$_2$O$_5$ there are weak but distinct spectroscopic changes that together with high resolution diffraction patterns suggest a lattice role at T$_{N}\sim $T$_{C}$, for the rare earth (R) replaced infrared spectra have as a main feature a broad band at meV energies in addition to progressive rotation of Mn-O polyhedra. That band, independent of the R$^{3+}$ ion size and common to all, suggests hopping of carriers through fluctuations at a local scale. It partially condenses below 40 K, i.e., the collective electronic behavior changes from delocalized to one partially localized. We assimilate that condensate to a CDW-like phase mode. It might indicate induced orbital correlation of charge transfers between Mn sites.Frequency Raman phonon shifts are observed at T$\sim $60 K, due to spin-phonon coupling, and at T$_{N}\sim $T$_{C}$. Below T$_{N}\sim $T$_{C}$ there is no a Raman soft mode that might be associated to a CDW amplitude mode. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:27PM |
B17.00009: Korringa-like relaxation in $A$-site ordered manganites S. Schaile, H.-A. Krug von Nidda, A. Loidl, J. Deisenhofer, T. Nakajima, Y. Ueda Half doped manganites exhibiting charge- and orbital ordering transitions are paradigm materials for studying colossal magnetoresistance, the existence of ferroelectricity or Zener polaron-type features. We report on high-temperature electron spin resonance studies of $A$-site ordered and disordered $A$BaMn$_2$O$_6$ $A=$Y,Sm,La. We find a Korringa-like spin-relaxation above the charge-ordering transition and extending up to 1000~K in the $A$-site ordered antiferromagnetic systems $A=$Y,Sm, a unique feature for a truly metallic state not having been reported in manganites before. In agreement with the ESR intensity this finding suggests that the ESR signal stems from Mn$^{4+}$ core spins which relax via the quasi-delocalized $e_g$ electrons. In contrast in the disordered AFM and the ferromagnetic samples no Korringa relaxation is observed. Hence, the conductivity does not significantly influence the spin relaxation in those compounds. [Preview Abstract] |
Monday, March 21, 2011 1:27PM - 1:39PM |
B17.00010: Magnetic order in La$_{1-x}$Ca$_{x}$MnO$_{3}$ nanopowder Chetan Dhital, Clarina Dela Cruz, Kefong Wang, Jun-Ming Liu, Zhifeng Ren, Stephen Wilson Here we present neutron diffraction studies exploring the spin behavior in nanocrystalline La$_{1-x}$Ca$_{x}$MnO$_{3}$ (LCMO). Confinement effects and the influence of phase separation have long been key issues within the underlying electronic behavior of the manganites. The coexistence of competing electronic phases has been reported across length scales exceeding 100nm in bulk manganites in proximity of the first-order metal-to-insulator phase transition in their phase diagrams. When the grain size of manganite crystals approaches the size of intrinsically phase-separated domains, new magnetic phases can be stabilized and the resulting electronic behavior dramatically altered. In this talk, we present results from our recent investigations of the magnetism in LCMO samples whose grain-size has been reduced to the nanometer scale. Newly stabilized static spin order and its relevance to phase separation in this manganite system will be discussed. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B17.00011: Density functional investigation of the spin frustration and the field-driven long-range ordering in the honeycomb lattice system Bi$_{3}$Mn$_{4}$O$_{12}$(NO$_{3})$ Jia Liu, Won-joon Son, Mike Whangbo Bi$_{3}$Mn$_{4}$O$_{12}$(NO$_{3})$, consisting of the honeycomb lattices of Mn$^{4+}$ (d$^{3})$ ions, has dominant antiferromagnetic interactions ($\theta _{CW}=-$257 K) but its spins do not order down to 0.4 K. However, applied magnetic fields induce a long-range magnetic order, which is believed to arise from the spin canting due to the Dzyaloshinskii-Moriya interaction. To explain these observations, we examined the spin exchanges between the Mn$^{4+}$ ions (J$_{1}$, J$_{2}$, J$_{c})$ by DFT+U calculations and the preferred orientation of their spins by DFT+U+SOC calculations. The spin frustration is reproduced by U close to zero with J$_{2}$/J$_{1}$ $\approx $ 1/2. The cause for the field-induced long-range magnetic ordering was explored on the basis of DFT+U+SOC calculations. [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B17.00012: New magnetic structures in novel and conventional manganites Aziz Daoud-aladine, Juan Rodr\'Iguez-Carvajal, Cristian Perca, Loreynne Pinsard-Gaudart The determination of the magnetic structures of manganites has always been at the root of their fundamental understanding [1]. We studied the magnetic structures of half-doped charge ordered manganites that are either show the prototype [1] CE-type magnetic structure (Pr$_{1/2}$Ca$_{1/2}$MnO$_{3}$), or variants of this order (YBaMn$_2$O$_{6}$ [2] and Pr$_{0.6}$Ca$_{0.4}$MnO$_{3} $) with neutron diffraction. The study of Pr$_{1/2}$Ca$_{1/2}$MnO$_{3}$ (ILL, France) is the first ever done on a single crystal and it essentially confirms the pioneering picture [1], whereas the NPD studies of YBaMn$_2$O$_{6}$ [2] (PSI, Switzerland) and Pr$_{0.6}$Ca$_{0.4}$MnO$_{3}$ [3] (ISIS, UK), give two unprecedented results. The YBaMn$_2$O$_{6}$ magnetic structure corroborates the hotly debated ordering of Zener Polarons [4], and high resolution NPD data evidence a new spin reorientation transition around T$\sim$20K far below its TN$\sim170K$ in Pr$_ {0.6}$Ca$_{0.4}$MnO$_{3}$ [3] that has so far only been vaguely observed. We will discuss the consequences that these results have on the still hotly debated understanding of the connection between charge/orbital and spin orderings in the manganites. [1] Wollan, E.O. and Koehler, W.C. Rev. 100, 545 (1955) [2] A. Daoud-Aladine et al., Phys. Rev. Lett.: 101 166404 (2008) [3] A. Daoud-Aladine et al., unpublished [4] M. Coey Nature 430, 155-157 (8 July 2004) [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B17.00013: ABSTRACT WITHDRAWN |
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