Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A23: Focus Session: Manganites I |
Hide Abstracts |
Sponsoring Units: DMP GMAG Chair: J. J. Neumeier, Montana State University Room: Morial Convention Center 215 |
Monday, March 10, 2008 8:00AM - 8:36AM |
A23.00001: Sliding charge density wave in manganites Invited Speaker: Stripe and checkerboard phases appear in many metal oxide compounds, and are thought to be linked to exotic behaviour such as high temperature superconductivity and colossal magnetoresistance. It is therefore extremely important to understand the fundamental nature of such phases. The so-called stripe phase of the manganites has long been interpreted as the localisation of charge at atomic sites. Here, we present resistance measurements on La$_{0.50}$Ca$_{0.50}$MnO$_3$ which strongly suggest that this state is in fact a prototypical charge density wave (CDW) which undergoes collective transport. Dramatic resistance hysteresis effects and broadband noise properties are observed, both of which are typical of sliding CDW systems. Moreover, the high levels of disorder typical of manganites result in behaviour similar to that of well-known disordered CDW materials. The CDW-type behaviour of the manganite superstructure suggests that unusual transport and structural properties do not require exotic physics, but could emerge when a well-understood phase (the CDW) coexists with disorder. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 8:48AM |
A23.00002: Polaron dynamics in La$_{0.7}$Ba$_{0.3}$MnO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Y. Chen, B. G. Ueland, J. W. Lynn, S. Barilo, Y. Mukovski, R. Privezentsev In the pervoskite manganites La$_{1-x}$A$_{x}$MnO$_{3}$ (Ca, Sr and Ba), the spin, lattice, charge and orbital degrees of freedom are intimately coupled , leading to a rich phase diagram. La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO) is a metallic ferromagnet at temperatures below T$_{c} \quad \sim $ 257 K and colossal magnetoresistivity is observed and associated with the formation of nanoscale polarons that develop at elevated temperatures with an ordering wave vector of $\sim $ (1/4,1/4,0). As the paramagnetic-insulating state is entered, a purely elastic component to the structural polaron scattering signals the development of the correlated polaron glass phase in LCMO. We investigated the structure and dynamics of these polarons through and above the ferromagnetic-metallic to paramagnetic-insulating transition by neutron scattering on single crystals of La$_{0.7}$Ba$_{0.3}$MnO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$. In contrast to LCMO, no static polaron correlations are observed, however, we find that dynamic polaron correlations exist. We have measured the energy and temperature dependence of the dynamic polaron correlations. The formation of the dynamic polarons is not directly related to T$_{c}$. [Preview Abstract] |
Monday, March 10, 2008 8:48AM - 9:00AM |
A23.00003: Composition Dependence of Polaron Formation and Dynamics in La$_{1-x}$Ca$_{x}$MnO$_{3}$ B.G. Ueland, Y. Chen, J.W. Lynn, Y.M. Mukovskii, R. Privezentsev The colossal magnetoresistive perovskites La$_{1-x}$Ca$_{x}$MnO$_{3}$ have generated much interest due to the intimate correlation between their magnetic and transport properties. It is well known that for the doping range 0.22$<$x$<$0.47 a transition from a paramagnetic insulating to a ferromagnetic metallic state occurs upon cooling below T$_{C}\sim $150-250 K, and experiments have shown that the transition between these states is closely tied to the formation of lattice polarons. Recent neutron scattering experiments have directly observed that these polarons freeze into a glassy state at T=T$_{c}$ for materials with x=0.33, which is responsible for the observed first order nature of the ferromagnetic transition at this level of doping. While it has been proposed that this glass state occurs as x$\sim $0, its dependence on doping and temperature has yet to be fully mapped out. Here we present results from elastic and inelastic neutron scattering experiments performed on single crystal samples of these materials for x=0.15, 0.2, and 0.25, which have been undertaken to determine the direction in which the boundary for the glass phase evolves with x. Preliminary results indicate that in the insulating state (x$<$0.22), no static polaron scattering is observed (in zero field), in contrast to the results for the metallic regime. [Preview Abstract] |
Monday, March 10, 2008 9:00AM - 9:12AM |
A23.00004: Current-induced persistent ferromagnetic metallic state in an Fe-doped manganite Hideaki Sakai, Yoshinori Tokura A persistent ferromagnetic metallic state has been observed to be induced by excitation of an electric current for a single crystal of 7\% Fe-doped (La$_{0.7}$Pr$_{0.3}$)$_{0.65}$Ca$_ {0.35}$MnO$_3$, a typical ``relaxor ferromagnet"[1] with coexisting clusters of the ferromagnetic metal and charge- orbital-ordered insulator. According to the simultaneous measurement of the resistance and magnetization, the induced ferromagnetic state is likely to form a filamentary pathway, where the increase in magnetization is estimated to be $\sim\!0.4$ $\mu_{\rm B}$ per Mn. Distinguishing the current heating effect, which tends to conversely decrease the ferromagnetic fraction, from the intrinsic effect, we have successfully demonstrated the reproducible switching of both the resistance and magnetization by changing the magnitudes of the applied voltages. \newline [1] H. Sakai {\it et al.}, Phys. Rev. B {\bf 76}, 155112 (2007). [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:24AM |
A23.00005: Terahertz time domain spectroscopy of ordered and disordered half-doped manganites K.R. Mavani, M. Nagai, H. Yada, K. Tanaka, D.S. Rana, I. Kawayama, M. Tonouchi Terahertz (THz) time domain spectroscopic studies were carried on Nd$_{0.5}$Ca$_{0.5}$MnO$_{3}$ and Nd$_{0.5}$Ca$_{0.48}$Ba$_{0.02}$MnO$_{3}$ (NCBMO) charge-ordered (CO) manganite thin films. Temperature dependent complex optical conductivity ($\tilde {\sigma }=\sigma _1 +i\sigma _2 )$ was studied to probe the cation disorder effects on low energy charge dynamics. The frequency dependent $\sigma _{1}$ suggests formation of charge-density-waves in these manganites. A doping induced cation disorder, as in the case of NCBMO, weakens the CO state.$^{1}$ However, at THz frequency, there are subtle effects of disorder on $\tilde {\sigma }$of NCBMO in a definite low temperature range. As temperature increases to 150 K (N\'{e}el temperature), changes are observed on the trends of temperature dependent dielectric constant ($\varepsilon _{1})$ and $\sigma _{1}$. The Ba doping effects are dominant above the charge-ordering transition temperature. The \textit{$\varepsilon $}$_{1}$ and \textit{$\sigma $}$_{1}$, both increase with temperature and show a scaling relationship, \textit{$\varepsilon $}$_{1~\propto }\sigma _{1}$, that is consistent with similar result observed for (PrCaSr)MnO$_{3}$ manganite.$^{2}$ $^{1}$Mavani \textit{et al.}, Europhys. Lett. (in print). $^{2}$Pimenove \textit{et al.}, Phys. Rev. B 73,220407(R). [Preview Abstract] |
Monday, March 10, 2008 9:24AM - 9:36AM |
A23.00006: High Magnetic Field Time-resolved Optical Study of Manganites. Paula Sahanggamu, Sanhita Ghosh, Stephen McGill, Haidong Zhou, Ben Conner, Christopher Wiebe We study the effects of applied electric fields and large magnetic fields on the optical properties of La$_{(1-x)}$Ca$_{x}$MnO$_{3}$ (x$\sim $0.18) (LCMO) and Pr$_{(1-x)}$Ca$_{x}$MnO$_{3}$ (x$\sim $0.5) (PCMO) using time-resolved techniques. Our measurements are performed from 4 K to room temperature and in dc magnetic fields up to 31 T. The conductivity of the low-temperature ferromagnetic state in LCMO is altered by the application of an electric field and these electrically-induced changes are further modified in the presence of an applied magnetic field. We demonstrate that time-resolved optical methods are capable of capturing these mixed electronic and magnetic effects. In addition, we performed time-resolved Kerr effect measurements in PCMO in an attempt to gain further insight into the loss of strong charge/orbital ordering in the presence of large applied magnetic fields. [Preview Abstract] |
Monday, March 10, 2008 9:36AM - 9:48AM |
A23.00007: Properties of Doped Manganese Oxides and the Origin of Colossal Magnetoresistance I. Felner, I. Nowik, D. Orgad, M. I. Tsindlekht, A. Frydman, D. I. Golosov, N. Ossi, Y. M. Mukovskii We report a series of magnetic and transport measurments on high-quality single crystal manganate samples in the colossal magnetoresistive (CMR) regime. A small iron doping allows also for a M\"{o}ssbauer spectroscopy study, showing both an unusual line broadening within the ferromagnetic phase and a coexistence of ferro- and paramagnetic contributions in the critical region. The resistivity peak (which gives rise to the CMR) occurs at a somewhat higher temperature, suggesting that it {\it does not} correspond to a threshhold of percolation between metallic (ferromagnetic) and insulating (paramagnetic) phases. In addition, our magnetic and transport data appear to imply that the paramagnetic-ferromagnetic (Curie) transition and the metal-insulator transition (the resistivity maximum) are two distinct phenomena on their own right, with distinct (although probably interrelated) physical origins. We speculate that these results can be understood phenomenologically within the framework of a two-fluid model. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:00AM |
A23.00008: Monte Carlo study of the one-orbital model for manganites in the CMR regime Rong Yu, Cengiz Sen, Gonzalo Alvarez, Elbio Dagotto The thermal phase transition in the one-orbital model for manganites with cooperative phonons and superexchange coupling is studied using Monte Carlo simulations. In the absence of on-site disorder, the model has a second order phase transition from a paramagnetic insulating phase to a ferromagnetic metallic phase in the CMR regime. The CMR effect is found to be associated with short-range charge and spin correlations in the insulating phase. This clearly shows that the CMR effect arises from the competition between the ferromagnetic and a charge-ordered competing states. Motivated by a recent STM experiment, we also studied the local density of states in this one-orbital model. We show how the experimental results can be understood within our model. [Preview Abstract] |
Monday, March 10, 2008 10:00AM - 10:12AM |
A23.00009: A New Correlated Model of Colossal Magnetoresistive Manganese Oxides D.I. Golosov A new minimal model is proposed for the doped manganese oxides which exhibit colossal magnetoresistance (CMR), involving (in addition to the ionic spins) a broad spin-majority conduction band as well as nearly localised spin-minority electron states. We outline the reasons to introduce this model, and discuss some of its properties. In particular, a mean field analysis yields an interaction-induced enhancement of the interband hybridisation and implies an emergence of a small energy scale, linked to the longitudinal spin dynamics, charge fluctuations, and presumably also to the carrier transport. We suggest that these conclusions merit further theoretical and experimental investigation in the context of the CMR manganates. [Preview Abstract] |
Monday, March 10, 2008 10:12AM - 10:24AM |
A23.00010: Combined Effect of Bond- and Potential-Disorder in Half-Doped Manganites Sanjeev Kumar, Arno Kampf We analyze the effects of both bond- and potential-disorder in the vicinity of a first-order metal insulator transition in a two-band model for manganites using a real-space Monte Carlo method. Our results reveal a novel charge-ordered state coexisting with spin-glass behavior. We provide the basis for understanding the phase diagrams of half-doped manganites, and contrast the effects of bond- and potential-disorder and the combination of both. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 10:36AM |
A23.00011: Nanoscale ferromagnetism and doping effect in manganites S. Mori, K. Yoshidome, Y. Horibe, T. Asaka, Y. Matsui, K. Takenaka We investigated temperature variation of ferromagnetic (FM) microstructures in La$_{1-x}$Sr$_{x}$MnO$_{3}$ (x=0.175) by low-temperature Lorentz microscopy. Also, changes of the FM domain structures by substituting non-magnetic Al$^{3+}$ ion for Mn one were examined. We succeeded in observing changes of magnetic domain structures from large FM domains with the average width of 1$\mu $m to stripe-shaped FM ones with the 100nm width in the metallic phase. On the other hand, the insulator phase was found in La$_{1-x}$Sr$_{x}$Mn$_{1-y}$Al$_{y}$O$_{3}$ (x=0.175, y=0.02). We found that the insulating phase exhibits a characteristic bi-modal distribution of the FM domains, which is characterized as the coexisting state of distinct types of the FM domains; one is the stripe-shaped FM domains and the other is the plate-shaped one. This mixture of distinct types of the FM domains breaks the coherence of the conductivity and results in the insulating character in La$_{1-x}$Sr$_{x}$Mn$_{1-y}$Al$_{y}$O$_{3}$ (x=0.175, y=0.02). In addition, we found the nanoscale FM domains around the rhombohedral-to-orthorhombic structural transition temperature in La$_{1-x}$Sr$_{x}$Mn$_{1-y}$Al$_{y}$O$_{3}$ (x=0.175, y=0.04). [Preview Abstract] |
Monday, March 10, 2008 10:36AM - 10:48AM |
A23.00012: Multiple Metal-Insulator Transitions in LPCMO Wires T.Z. Ward, S.H. Liang, K. Fuchigami, L.F. Yin, E. Daggotto, E.W. Plummer, J. Shen The two hottest areas of research in condensed matter physics are complexity and nanoscale physics. Interestingly, these two areas have little overlap as most of the nanophysics research work is conducted using ``simple'' materials of metals or semiconductors instead of complex materials such as transition metal oxides (TMOs). However, due to the strong electronic correlation, it is exactly the transition metal oxides that will most likely lead to observations of striking new phenomena under spatial confinement. In this work, spatially confined La$_{.325}$Pr$_{.3}$Ca$_{.375}$MnO$_{3}$ (LPCMO) is shown to exhibit never before seen transport properties which reveal a double metal-insulator transition. These findings shine new light on the processes at play in LPCMO, as we use this novel technique to probe the material. [Preview Abstract] |
Monday, March 10, 2008 10:48AM - 11:00AM |
A23.00013: Ferromagnetic tendencies at the surface of AF/CO bulk manganites Shuai Dong, Rong Yu, Seiji Yunoki, Elbio Dagotto Previous investigations have shown that the surface of a ferromagnetic (FM) manganite has antiferromagnetic (AFM) tendencies. However, the development of ferromagnetism has been observed experimentally in some AFM charge-ordered (CO) manganites by reducing the grain size down to the nanoscale. Similar phenomenon was also found in other nanosized CO oxides, such as La$_{1/3}$Sr$_{2/3}$FeO$_{3}$. To clarify these puzzling observations, using Monte Carlo techniques we studied the FM Kondo model, using open boundary conditions to simulate a surface. For some values of the couplings, the previously known tendency to an AFM outer shell was found for the case of a bulk FM state. But for other couplings, the opposite effect was observed: the existence of a FM layer at the surface of a AFM/CO material. Details will be provided in this presentation. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700