Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session P2: CM Pressure Effects on Electronic Structure |
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Chair: Duck Young Kim, Carnegie Institute of Washington Room: Grand Ballroom II |
Wednesday, July 10, 2013 11:00AM - 11:15AM |
P2.00001: ABSTRACT WITHDRAWN |
Wednesday, July 10, 2013 11:15AM - 11:30AM |
P2.00002: Pressure-Induced Valance change in Ytterbium Organometallic Molecule Cp*$_2$Yb(4,4'-Me$_{2}$-bipy) and Ytterbium intermetallic YbCuGa Farzana Nasreen, Daniel Antonio, Andrew Cornelius, Corwin H. Booth, Milton S. Torikachvili, Yuming Xiao We report on high pressure (0-15.3 GPa) x-ray absorption measurements in partial fluorescence yield mode (PFY-XAS) on two different kinds of Kondo systems - an organometallic molecular system Cp*$_{2}$Yb(4,4'-Me$_{2}$-bipy) [Cp$^{\ast}=$C$_{5}$Me$_{5}$, bipy $=$ (NC$_{5}$H$_{4})_{2}$ and Me $=$ CH$_{3}$] and an intermetallic YbCuGa system. In the organometallic system, similar to the mixed valency in intermetallic Yb Kondo systems, the CASSCF calculations indicate that the intermediate valence in the ground state is due to a configuration interaction between the open-shell [\textit{4f}$_{\uparrow}$$^{13}\pi_{\downarrow }^{\ast 1}$] and the closed-shell [\textit{4f}$_{\uparrow\downarrow}$$^{14}\pi^{\ast 0}$] spin-singlet states. Our analysis for Cp*$_{2}$Yb(4,4'-Me$_{2}$-bipy) shows that with increase in pressure the overall valency increases from 2.77 at 2.7 GPa to 2.97at 15.3 GPa. A considerable change in the slope of valency as function of pressure is observed at $\sim$3.26 GPa suggesting a valance transition. The Kondo effect in such molecular compounds is intrinsic and provides a well defined nanoscale system to test the effect of size on the strongly correlated behavior. In the YbCuGa bulk system, the increase in pressure delocalizes the system and pushes it from valency of $\sim$2.68 at ambient pressure to $\sim$2.9 at 14.0 GPa. [Preview Abstract] |
Wednesday, July 10, 2013 11:30AM - 11:45AM |
P2.00003: High-pressure Synchrotron M\"{o}ssbauer Spectroscopy on Fe$_{4}$O$_{5}$ Karunakar Kothapalli, Tomasz Kolodziej, Eunja Kim, Ercan Alp, Barbara Lavina Fe$_{4}$O$_{5}$ is a recently discovered compound belonging to the Fe-O binary system. We report the first insights on its properties as revealed by high pressure 57Fe Synchrotron M\"{o}ssbauer Spectroscopy (SMS) performed at several different pressures in the range 0-48GPa. Fe$_{4}$O$_{5}$ first synthesized in the diamond anvil cell at a pressure of about 10 GPa and 1800 K, is a high pressure phase recoverable in ambient conditions. It crystallizes in the orthorhombic \textit{Cmcm} spacegroup. The Fe atoms occupy three crystallographic positions -- the 4a and 8f octahedral sites and 4c trigonal prism site. The SMS spectra could be fitted with just a single site and the Hyperfine Magnetic Field(HF) and Quadrapole Splittings(QS) were derived. The magnitudes of HF and QS indicate that the major contribution originates from high-spin Fe$^{3+}$ ions. The HF and QS parameters show a linear dependence in the region 10-48 GPa. A significant change in QS below 10 GPa suggests a considerable deviation in the electronic contribution from the charge distribution of the surrounding electron shell. The magnetic structure and the pressure dependence of hyperfine parameters will be discussed in light of plausible contributions from the different Fe-sites and supporting theoretical calculations. [Preview Abstract] |
Wednesday, July 10, 2013 11:45AM - 12:00PM |
P2.00004: Magneto-Structural coupling in compressed Manganese Oxide Antonio M. dos Santos, Chris A. Tulk, Jamie J. Molaison, Neelam Pradhan Transition metal oxides are relevant systems for the earth sciences as these are ideal model systems for Earth's interior. In these systems, pressure increases the magnetic transition temperature, up to a point, where magnetic quenching is predicted. MnO orders magnetically at 118 K in a type II antiferromagnetic structure. This magnetic transition is accompanied by a first order structural transition, from the high temperature cubic paramagnetic phase to a low temperature rhombohedral structure [1], and is well correlated with the magnetic ordering [2]. Interestingly, although magnetic ordering at room temperature is expected only at 60 GPa, a sharp anomaly in the resistivity data has been detected below 10 GPa [3]. Here we present recent results at SNAP at the SNS where high-pressure low-temperature neutron powder diffraction data were collected up to 10 GPa. These data allow determination of the increase of Tc with pressure and characterize the strength of the magneto-structural coupling in MnO when magnetic ordering is induced by pressure.\\[4pt] [1] Tombs NC, Rooksby HP, Nature 165(4194): 442-443 (1950)\\[0pt] [2] Kantor AP, et.al, J. Alloys and Comp. : 402(1-2): 42-45 (2005) \\[0pt] [3] Minomura S. and Drickamer H. G. J. App. Phys. 34, 3043 (1963) [Preview Abstract] |
Wednesday, July 10, 2013 12:00PM - 12:15PM |
P2.00005: High Pressure M\"{o}ssbauer Spectroscopic Studies on Narrow Band Co$_{1-x}$Fe$_{\mathrm{x}}$S$_{2}$ Systems up to 9GPa Usha Chandra Pyrite type 3d-transition metal disulfides exhibit a wide variety of interesting electrical and magnetic properties. CoS$_{2}$ is a ferromagnetic metal ordering ferromagnetically below $\sim$120K while FeS$_{2}$ is a narrow band gap diamagnetic semiconductor. Both Co and Fe are in low spin configuration. Formation of solid solutions between these two end members opens up the possibility of tuning the position of Fermi level in Co$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$S$_{2}$. Nano crystalline systems Co$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$S$_{2}$ (x$=$0.1 to 1.0) identically synthesized adopting solution technique were characterized by XRD, TEM. All the systems except x$=$0.8 showed nano sized particles. TEM micrographs taken for Co$_{0.2}$Fe$_{0.8}$S$_{2}$ system showed nano wires formation with SAED images indicating crystalline pattern. Electrical resistivity of bulk Ferromagnetic pyrite compounds Fe$_{\mathrm{x}}$Co$_{\mathrm{1-x}}$S$_{2}$ have shown an anomalous temperature dependence with increasing magnetic order below curie temperature due to the effect of a change in band width. Shift in the absorption edge with pressure in bulk pyrite FeS$_{2}$ has been attributed to large compaction of S-S bonds in comparison to Fe-S bonds. $^{57}$Fe M\"{o}ssbauer spectroscopic investigations on systems under high pressure are sensitive enough to probe variations in valence, spin configuration and site occupancy of Fe. The high pressure M\"{o}ssbauer spectroscopic measurements using diamond anvil cell on nano crystalline Co$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$S$_{2}$ (x$=$0.2,0.5 and 0.8) would be reported to understand the pressure effect on band gap. [Preview Abstract] |
Wednesday, July 10, 2013 12:15PM - 12:30PM |
P2.00006: Effect of Hydrostatic Pressure on Magnetic Caloric Effect of Charge - Orbital Order Perovskite manganite Pr(Sr$_{0.6}$Ca$_{0.4}$)$_2$Mn$_2$O$_7$ Arumugam S, Thiyagarajan R, Mohan Radheep D, Esakki Muthu S, Guochu Deng, Ekaterina Pomjakushina, Kazimierz Conder The effect of hydrostatic pressure and magnetic field on magnetic and magnetocaloric properties of half-doped bilayer manganite single crystal Pr(Sr$_{0.6}$Ca$_{0.4})_{2}$Mn$_{2}$O$_{7}$ has been investigated. The sample undergoes an antiferromagnetic (AF) transition at 103 K and a Charge-Orbital ordering (CO) at 179 K under ambient pressure with field of 0.5 T in c-axis. In CO ordered state, magnetization along c-axis shows the hysteresis which represents the first order phase transition and it is enhanced by both H and P. Simultaneously, magnetic caloric effect ($\Delta S_{m})$ and Relative Cooling Power (RCP) around T$_{\mathrm{CO}}$ were increased by the application of the magnetic field and hydrostatic pressure. Although magnitude of $\Delta S_{m}$ is small compared to other conventional ferromagnetic manganites, this study may help to understand the effect of pressure on Magnetic Caloric Effect in antiferromagnetic manganites, especially, bilayer manganites. Further, RCP value gets increased in isothermal magnetization under $P$. Hence, Pr(Sr$_{0.6}$Ca$_{0.4})_{2}$Mn$_{2}$O$_{7}$ may be a potential candidate for magnetic refrigeration applications. [Preview Abstract] |
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