Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session B41: Cooperative Phenomena: Magnetism |
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Sponsoring Units: GMAG Chair: Mark Van Schilfgaarde, Arizona State University Room: LACC 150A |
Monday, March 21, 2005 11:15AM - 11:27AM |
B41.00001: Magnetic properties of single crystal Pr$_5$Ni$_2$Si$_3$ R.W. McCallum$^{1,2}$, Y. Janssen$^1$, K.W. Dennis$^1$, P.C. Canfield$^{1,3}$ Pr$_{5}$Ni$_{2}$Si$_{3}$ is the n = 3 member of the series, R$_{(n+2)(n+1)}$Ni $_{n(n-1)+2 }$Si$_{n(n+1)}$, which consists of three compounds with n = 2, 3 and 4. These phases exhibit similar hexagonal crystal structures and as a result, their physical properties are expected to vary systematically. Pr$_{5}$Ni$_{2}$Si$_{3}$ orders with a net moment along the c-axis at $\sim $50 K. A sharp $\lambda $ anomaly in the specific heat is observed at the ordering temperature, and a shoulder is observed at lower temperatures. The saturated moment parallel to c (M$\vert \vert $c) at 5 K is 2 $\mu _{B}$/Pr compared to the full Pr moment of 3.2 $\mu _{B}$. At 5 K M$\bot $c/ M$\vert \vert $c = 0.05 at 1T, and undergoes a broad step to M$\bot $c/ M$\vert \vert $c =0.5 between 2.5 and 3.5 T. As T is increased the step becomes less pronounced and shifts to lower fields. These results are tentatively attributed to two almost degenerate magnetic states, one ferro or ferrimagnetic and the other conical. Ames Laboratory is operated for the US Department of Energy by Iowa State University under contract number W-7405-ENG-82. [Preview Abstract] |
Monday, March 21, 2005 11:27AM - 11:39AM |
B41.00002: Thermal Expansion and Magnetostriction in Pr5Ni2Si3 Single crystal S.H. Song, J.E. Snyder, D. Wu, T.A. Lograsso, K.W. Dennis, R.W. McCallum, Y. Janssen, D.C. Jiles Pr$_{5}$Ni$_{2}$Si$_{3}$ is the second member of the series, R$_{(n+2)(n+1)}$Ni$_{n(n-1)+2}$Si$_{n(n+1)}$, which consists of three compounds with n= 2,3 and 4 with similar hexagonal crystal structures and exhibiting uniaxial magnetic anisotropy with an easy c axis. In this study, thermal expansion and magnetostriction of Pr$_{5}$Ni$_{2}$Si$_{3}$ single crystals were investigated parallel and perpendicular to the easy axis over the temperature range of 5 to 300 K under applied magnetic field up to 9 T. The magnetic contribution to the thermal expansion was determined by approximating the phonon contributions to thermal expansion using the Debye-Gruneisen model. The results reflect two different magnetic phase transformations upon cooling, one corresponding to the Curie temperature (41 K) and the other exhibiting characteristics of a spin reorientation. Ames Lab. is operated for the US Department of Energy by Iowa State University under contract number W-7405-ENG-82. [Preview Abstract] |
Monday, March 21, 2005 11:39AM - 11:51AM |
B41.00003: Magnetic and transport properties of Fe1-xCoxSb2 Cedomir Petrovic, Yongjae Lee, Thomas Vogt Single crystals of Fe1-xCoxSb2 have been grown by molten metallic flux technique. Synchrotron powder x-ray diffraction confirms phase purity and orthorhombic Pnnm space group. Cobalt substitution drives system from diamagnetic semiconductor to metallic ferromagnet at T=0 with very small ordered moment. Application of magnetic field leads to large magnetoresistance [R(H)-R(0)]/ R (0) = 185 at T=2K. The results are discussed in connection with possible Kondo Insulator description of FeSb2. [Preview Abstract] |
Monday, March 21, 2005 11:51AM - 12:03PM |
B41.00004: Thermal-expansion and elastic properties of CeRhIn$_5$ and YbInCu$_4$ in high magnetic fields Victor Correa, Jonathan Betts, Albert Migliori, John Sarrao, Alex Lacerda, Winston Okraku We present high magnetic field thermal-expansion and magnetostriction results on CeRhIn$_5$ single crystals. Several transitions, both first and second order, are observed when the field is applied perpendicular to the crystallographic c-axis. The magnetic field dependence of the thermal-expansion coefficient above 15 K, where the magnetic correlations are negligible, can be explained supposing an almost pure $| \pm 5/2 \rangle$ ground state doublet, in apparent contradiction with neutron scattering experiments. Although the spin-lattice interaction is relevant in this compound, the effect of the magnetic correlations on the elastic properties is relatively weak, as revealed by resonant ultrasound spectroscopy experiments. We present also magnetovolume studies in YbInCu$_4$ using a capacitive dilatometer in a pulsed magnetic field. [Preview Abstract] |
Monday, March 21, 2005 12:03PM - 12:15PM |
B41.00005: ESR of Gd$^{3+}$ in the Intermediate Valence YbAl$_{3}$ and its Reference Compound LuAl$_{3}$ R.R. Urbano, M.A. Pires, E.M. Bittar, C. Rettori, P.G. Pagliuso, B. Magill, S. Oseroff Electron Spin Resonance (ESR) experiments were performed on Gd$^ {3+}$ doped YbAl$_{3}$ intermediate-valence (IV) compound and its reference compound LuAl% $_{3}$. A Korringa rate, $d(\Delta H)/dT\simeq 14$ Oe/K, and a negative $g$ shift, $\Delta g\simeq 0.01,$ are obtained for Yb$_{0.996}$Gd$_ {0.004}$Al$% _{3}.$ These data are compared to a smaller positive $g$ shift and Korringa rate found for the reference Lu-based compound. Our results suggest that the density of states at the Fermi level is built up of multiple bands for both materials. Effects associated with the low temperature energy scale ($% T\simeq 10$ K) of YbAl$_{3}$ are taken into account to interpret our ESR results. Magnetic susceptibility and specific heat measurements are also presented. [Preview Abstract] |
Monday, March 21, 2005 12:15PM - 12:27PM |
B41.00006: Magnon-Plasmon Interaction David Wisbey, Hae-Kyung Jeong, Ralph Skomski, Peter Dowben Spin polarized plasmons of the strained Gd on Mo(112), as well as a spin-polarized Drude tail, are observed using spin polarized electron energy loss spectroscopy. Bulk plasmon is dominated more by spin majority character at zone center than spin minority, while the surface plasmon or multipole plasmon like loss is more of spin minority character at zone center. The spin minority character of the surface plasmon increasingly dominates the spin-polarized electron energy loss spectra as the wave vector increases. [Preview Abstract] |
Monday, March 21, 2005 12:27PM - 12:39PM |
B41.00007: High energy magnetic excitations in Cr Hyungje Woo, E. Clementyev, P. B\"oni, M. Fujita, T.G. Perring, S.M. Hayden, G. Shirane Pure Cr has a simple bcc structure but the magnetism is known to be rather complicated, and so far its properties are not yet understood well [1]. Below $T_{N} = 311 K$ it is antiferromagnetic (AF) with an incommensurate (IC) spin density wave showing long-range order. We have used inelastic neutron scattering to map the dynamics of the spin density wave in a single-Q (i.e. untwined) single crystal of Chromium. We observe fluctuations of the magnetism wavevectors corresponding to the commensurate (1, 0, 0), the allowed IC positions (1$\pm\delta$, 0, 0) and the silent IC positions (0, 1$\pm\delta$, 0) at energies up to 83 meV. Interestingly, as the energy of the fluctuations increases, spectral weight moves from the IC peaks to smaller $\delta$, becoming commensurate at around 64 meV. This behaviour, namely IC AF fluctuations that move to the commensurate position, is also a common feature observed in high-TC superconductors such YBa$_{2}$Cu$_{3}$O$_{6.6}$ [2], La$_{15/8}$Ba$_{1/8}$CuO$_{4}$ [3], and La$_{1.84}$Sr$_{0.16}$CuO$_{4}$ [4]. An understanding of the magnetism in the itinerant AF Chromium may well help unravel that in the high-TC superconductors. [1] E. Fawcett, Rev. Mod. Phys. 60, 209 (1988). [2] Hayden et. al. Nature 429, 531 ('04). [3] Tranquada et. al. Nature 429, 534 ('04). [4] Christensen et. al. Phys. Rev. Lett. 93, 147002 (2004). [Preview Abstract] |
Monday, March 21, 2005 12:39PM - 12:51PM |
B41.00008: On the noncollinear magnetic structure of UO2 Raquel Liz\'arraga, Massimiliano Colarieti-Tosti, Olle Eriksson, Lars Nordstr\"om , John Wills Recent neutron diffraction measurements on UO$_2$ under high magnetic field predicts a triple-{\bf k} structure associated with a triple-{\bf k} distortion of the oxygen sublattice. We have performed first principles calculations on the magnetic structure of UO$_2$ using the full potential augmented plane wave with local orbitals at ambient conditions. We have investigated two transversal and a longitudinal triple-{\bf k} structures with the experimentally suggested triple-{\bf k} oxygen distortion. [Preview Abstract] |
Monday, March 21, 2005 12:51PM - 1:03PM |
B41.00009: Hybrid functional description of the rhombohedrally distorted B1-structured MnO Cesare Franchini, Robin Hirshl, Georg Kresse, Veronika Bayer, Raimund Podloucky We report a first principle calculation of the ground state properties of MnO within the plane wave based PBE0 hybrid density functional approach developed on the projector augmented wave scheme VASP (Vienna \textit{ab initio} Simulation Package). The insulating, antiferromagnetically ordered and rhombohedrally distorted B1 structure is found to be the most stable phase, consistent with experiment. The gap (4.02 eV), magnetic moment (4.52 m{\_}B), optimum lattice constant (4.40 A), rhombohedral distortion angle (0.88), density of states, and exchange integrals, are all in good agreement with experiment. Our findings confirm the picture which places MnO in the intermediate charge-transfer/Mott-Hubbard regime and suggest that the parameter-free PBE0 hybrid functional method, combining the full nonlocal exact exchange interaction with the PBE exchange-correlation functional well correct the deficiency of conventional DFT, thus providing a accurate description of this correlated material. [Preview Abstract] |
Monday, March 21, 2005 1:03PM - 1:15PM |
B41.00010: Single field-induced phase in U(Ru1-xRhx)2Si2 at a Quantum Critical Point Alejandro Silhanek, Victor Fanelli, Marcelo Jaime, Neil Harrison, H. Amitsuka, John Mydosh A detailed analysis of the specific heat and magneto-caloric effect is carried out in the heavy fermion system U(Ru$_{1-x}$Rh$_{x})_{2}$Si$_{2}$ with x=4{\%}. This compound exhibits a much simpler $H-T$ phase diagram than the stoichiometric parent URu$_{2}$Si$_{2}$, with a single field-induced magnetic phase, known as phase II, surrounding a quantum critical point. We show that the boundary of this phase II corresponds to a first order transition as revealed by a large specific heat anomaly and an asymmetric magnetocaloric effect between entering and exiting the phase. An anomalous history and time dependent specific heat support this interpretation. We argue that the observed irreversibilities might be associated with a structural transformation in the crystal lattice. [Preview Abstract] |
Monday, March 21, 2005 1:15PM - 1:27PM |
B41.00011: Theory of Paramagnetic Susceptibility of Heavy-Fermion Systems Prasanta Misra, B.G. Mahanty, Gouri Tripathi We consider a periodic Anderson Hamiltonian in the presence of an applied magnetic field. We derive an expression for the paramagnetic susceptibility of an itinerant electron system in the presence of conduction electron moment and localized moment (c-l)hybridization. We derive an expression for the spin susceptibility of the itinerant electron system and express it as a sum of the exchange enhanced Pauli spin susceptibility and a part which is written as a product of electron paramagnetic resonance (EPR) shift and the Curie-Weiss susceptibilty. The EPR shift is very much similar to the Knight shift, if a contact interaction for the c-l hybridization is assumed. There is good qualitative agreement with the experimental results for CeRu2Si2. [Preview Abstract] |
Monday, March 21, 2005 1:27PM - 1:39PM |
B41.00012: Magnetic and Resistive Properties of Annealing of Radiation Damage in Pu and Pu Alloys Michael Fluss, Scott McCall, Brandon Chung, George Chapline, Michael McElfresh, Damon Jackson We report a high fidelity radiation damage-isochronal annealing curve based on changes in magnetic susceptibility for $\alpha $-phase Pu from 5-350K with Stage-I annealing at $>$30K and complete annealing at $\sim $315K. These results, while based on changes in magnetic susceptibility, are surprisingly similar to resistivity data reported 40 years ago by Wigley (\textit{Proc. R. Soc.} \textbf{A 284} (1964) 344) and suggest the excess magnetic susceptibility (EMS) is the result of accumulated radiation damage. Additionally, we report the excess magnetic susceptibility as a function of temperature for vacancies alone. We conclude that the vacancy induced EMS shows an inverse-temperature dependence that is much stronger than interstitial induced excess magnetic susceptibility. These results will be compared with resistivity studies of radiation damage accumulation in fcc delta phase Pu( 3.3 at{\%} Ga) (M.J. Fluss \textit{et. al}, \textit{J. of Alloys and Compds.} \textbf{368} (2004) 62--74), where vacancies and vacancy cluster resistance was reported to behave in an anomalous manner with respect to temperature by being proportional to --\textit{ln(T)}, and thus suggesting local moments with a low critical temperature. The possible role of disorder in stabilizing the low density delta phase of Pu will be discussed. \textit{Work performed under the auspices of the U. S. DOE by LLNL; contract W-7405-Eng-48.} [Preview Abstract] |
Monday, March 21, 2005 1:39PM - 1:51PM |
B41.00013: Excess Magnetic Susceptibility Arising from Self damage in Alpha-Pu Scott McCall, Michael Fluss, Brandon Chung, George Chapline, Michael McElfresh, Damon Jackson The $f-$electrons of plutonium are delicately poised on the edge between localized and itinerant behavior. In the case of $\alpha -$Pu, the electrons are nearly localized in a narrow $f-$band and the Pauli magnetic susceptibility is the largest of any element. Low temperature magnetic susceptibility measurements on $\alpha -$Pu show that the magnetic susceptibility increases as a function of time, yet upon annealing the specimen at 350K, it returns to its initial value. This suggests that the excess magnetic susceptibility,\textit{ $\chi $}$_{xs}(t,T)$, arises from the $\alpha $-decay and U recoil damage cascades which produce vacancy and interstitials as point and extended defects. The time dependence of \textit{$\chi $}$_{xs}$ is well described by \textit{$\chi $}$_{xs}$\textit{$\sim $a(1-exp(-t/$\tau )$}) where $a$ and \textit{$\tau $} are both functions of temperature. At short times, \textit{$\chi $}$_{xs}$\textit{(T$<$30),} may be fit to a Curie-Weiss law. However, as \textit{t--$>\infty $}, \textit{$\chi $}$_{xs}$\textit{(T$<$30) --$>$ T}$^{-1}$ implying that self-damage may drive Pu towards non-Fermi liquid behavior. \textit{This work was performed under the auspices of the U. S. DOE by Lawrence Livermore National Laboratory, under contract W-7405-Eng-48.} [Preview Abstract] |
Monday, March 21, 2005 1:51PM - 2:03PM |
B41.00014: Magnetic X-ray Scattering from Cuprates Z. Islam, D. Haskel, J.C. Lang, G. Srajer, X. Liu, S.K. Sinha, B.W. Veal Magnetic x-ray scattering studies of ordered spin-$\frac12$ copper moments in cuprates have been difficult to perform. While resonant scattering has been studied in one sample of Pr-barium cuprate ({\it PRB} {\bf 61}, 1251 (2000)), a direct observation of non-resonant scattering from cuprates ({\it e.g.} YBa$_2$Cu$_3$O$_{6+x}$, YBCO) has not been made. We have succeeded in observing non-resonant magnetic scattering of x- rays from antiferromagnetically ordered YBCO insulators. Magnetic Bragg peaks characterized by ($\frac12$, $\frac12$, 0) were found to be resolution limited in all directions revealing correlation lengths of $\sim$1000 A. By using a polarization analyzer to exactly suppress charge scattering we were able to obtain a peak-to-background ratio of $\sim$7 with a peak count rate of 2- 3 counts/second. Q-dependence of the intensities is consistent with the known structure and scattering cross section. Our study demonstrates the feasibility of such a technique at a third generation synchrotron source, which can be used for studying very small samples. [Preview Abstract] |
Monday, March 21, 2005 2:03PM - 2:15PM |
B41.00015: Pressure Induced Valence Changes in YbAl$_3$ Studied by Resonant Inelastic X-Ray Emission Andrew Cornelius, Ravhi Kumar, Malcolm Nicol, Michael Hu, Eric Bauer, John Sarrao We have performed high resolution x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) experiments to probe the pressure dependence of Yb valence in YbAl$_{3}$ up to 38 GPa. XAS spectra were collected in the partial fluorescence yield (PFY) mode with a Si (333) analyzer at the Yb L$_{3}$ edge. The RIXS spectra were recorded by fixing the incident energy and collecting the transferred energy as a function of pressure in 2 eV steps. The results showed a continuous valence change from intermediate (between 2+ to 3+) towards trivalent due to enhancement of 4f hybridization similar to other mixed valent Yb heavy fermion compounds under pressure [1, 2]. The 2+ to 3+ conversion of the valence state of Yb is almost complete above 29 GPa. The results, along with x-ray diffraction measurements, will be presented in detail. 1. C. Dallera, M. Grioni, A. Shukla, G. Vanko, J. L. Sarrao, J. P. Rueff and D. L. Cox Phys. Rev. Lett., 88, 196403 (2002) 2. C. Dallera, E. Annese, J. P. Rueff, A. Palenzona, G. Vanko, L. Braicovich, A. Shukla and M. Grioni, Phys. Rev. B., 68, 245114 (2003) [Preview Abstract] |
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