Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y19: Correlated Electron Magnetism |
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Sponsoring Units: GMAG DCMP Chair: Steven Disseler, NIST Room: 318 |
Friday, March 18, 2016 11:15AM - 11:27AM |
Y19.00001: Orbital Delocalization and Enhancement of Magnetic Interactions in Perovskite Oxyhydrides Kai Liu, Yusheng Hou, Xingao Gong, Hongjun Xiang Recent experiments showed that some perovskite oxyhydrides have surprisingly high magnetic-transition temperature. In order to unveil the origin of this interesting phenomenon, we investigate the magnetism in SrCrO$_{\mathrm{2}}$H and SrVO$_{\mathrm{2}}$H on the basis of first-principles calculations and Monte Carlo simulations. Our work indicates that the Cr-O-Cr superexchange interaction in SrCrO$_{\mathrm{2}}$H is unexpectedly strong. Different from the previous explanation in terms of the H$^{\mathrm{-}}$ ion substitution induced increase of the Cr-O-Cr bond angle, we reveal instead that this is mainly because the 3$d$ orbitals in perovskite oxyhydrides becomes more delocalized since H$^{\mathrm{-}}$ ions have weaker electronegativity and less electrons than O$^{\mathrm{2-}}$ ions. The delocalized 3$d$ orbitals result in stronger Cr-O interactions and enhance the magnetic-transition temperature. This novel mechanism is also applicable to the case of SrVO$_{\mathrm{2}}$H. Furthermore, we predict that SrFeO$_{\mathrm{2}}$H will have unprecedented high Neel temperature because of the extraordinarily strong Fe-H-Fe $\sigma $-type interactions. Our work suggests the anion substitution can be used to effectively manipulate the magnetic properties of perovskite compounds. [Preview Abstract] |
Friday, March 18, 2016 11:27AM - 11:39AM |
Y19.00002: \textbf{Understanding the magnetoelastic behavior of pure and Co substituted GdNi} Durga Paudyal, Y. Mudryk, V. K. Pecharsky, K. A. Gschneidner, Jr. Total-energy calculations employing local spin density approximation including Hubbard $U$ (onsite electron correlation) parameter and temperature and magnetic field dependent x-ray diffraction experiments show large anisotropic shifts in lattice parameters and a giant linear magnetostriction without a structural transformation and a negligible volume magnetostriction in GdNi. In agreement with the magnetization and heat-capacity experiments, the total-energy and band splitting results confirm that the anisotropic shape changes in GdNi are associated with the second-order ferromagnetic to paramagnetic transformation. When the band splitting due to the ferromagnetic ordering of the 4$f $moments increases, the concomitant anisotropic changes in the lattice minimize the total free energy of the crystal indicating an unusual interplay between magnetism and crystal structure. The positive formation energy at 0K and the nature of the density of states at the Fermi level confirm an unstable equiatomic Gd compound when Ni is fully substituted by Co. However, the enhanced effective exchange interactions with small Co substitutions increase the Curie temperature without losing the chemical stability. [Preview Abstract] |
Friday, March 18, 2016 11:39AM - 11:51AM |
Y19.00003: \textbf{Direct observation of a helical magnetic order near the superconducting state of MnP under pressure} Yishu Wang, Yejun Feng, J.-G. Cheng, T. F. Rosenbaum A recent high-pressure electrical transport study of the 3d transition metal compound MnP manifested a complex pressure-temperature phase diagram of different types of magnetism and superconductivity. However, the nature of the high-pressure magnetic phase proximate to the superconducting state was not determined. We use non-resonant X-ray magnetic diffraction to probe the magnetic order in MnP under pressure. We discover incommensurate helical order in a confined region under high pressure, and ascertain the phase boundary through the pressure evolution of the lattice. Although the antiferromagnetic and superconducting phases are separated, there is no signature of a strong first-order phase transition between them. We discuss how our direct observation of a helimagnetic order in MnP helps to better understand aspects of magnetically-mediated superconductivity. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:03PM |
Y19.00004: Neutron scattering study on the magnetic and superconducting phases of MnP Shinichiro Yano, Diane Lancon, Henrik Ronnow, Thomas Hansen, Jason Gardner We have performed series of neutron scattering experiments on MnP. MnP has been investigated for decades because of its rich magnetic phase diagram. The magnetic structure of MnP is ferromagnetic (FM) below $T_{C}$ = 291 K. It transforms into a helimagnetic structure at $T_{S}$ = 47 K with a propagation vector $q = 0.117 a^{*}$. Superconductivity was found in MnP under pressures of 8 GPa with a $T_{SC}$ around 1 K by J.-G. Cheng. Since Mn-based superconductors are rare, and the superconducting phase occurs in the vicinity of FM, new magnetic and helimagnetic phases, there is a need to understand how the magnetism evolves as one approach the superconducting state. MnP is believed to be a double helix magnetic structure at $T_{S}$ = 47 K. We observed new 2$\delta$ and 3$\delta$ satellite peaks whose intensity are 200 $\sim$ 1000 times smaller than these of 1$\delta$ satellite peaks on the cold triple axis spectrometer SIKA under zero magnetic fields. We also found the periods of helimagnetic structure changes as a function of temperature. If time permits, we will discuss recent experiments under pressure. However, we have complete picture of magnetic structure of this system with and without applied pressure, revealing the interplay between the magnetic and superconducting phases. [Preview Abstract] |
Friday, March 18, 2016 12:03PM - 12:15PM |
Y19.00005: Unusual behavior of uranium dioxide at high magnetic fields. Part I K. Gofryk, M. Jaime, V. Zapf, N. Harrison, A. Saul, G. Radtke, J. C. Lashley, M. Salamon, A. D. Andersson, C. Stanek, T. Durakiewicz, J. L. Smith UO$_{2}$ is a Mott-Hubbard insulator with well-localized 5$f$-electrons and its crystal structure is the face-centered-cubic fluorite. It experiences a first-order antiferromagnetic phase transition at 30.8 K to a non-collinear antiferromagnetic structure that remains a topic of debate. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion of oxygen atoms. Despite extensive experimental and theoretical efforts the nature of the competing degrees of freedom and their couplings (such as spin-phonon coupling) are still unclear. Here we present results of our extensive thermodynamic investigations, on well-characterized and oriented single crystals of UO$_{2}$, focusing on magnetization M(T,H) measurements in DC and pulsed magnetic fields to up 65 T at the NHMFL. [Preview Abstract] |
Friday, March 18, 2016 12:15PM - 12:27PM |
Y19.00006: Unusual behavior of uranium dioxide at high magnetic fields. Part II$^{\ast }$. M. Jaime, K. Gofryk, V. Zapf, N. Harrison, A. Saul, G. Radtke, J.C. Lashley, M. Salamon, A.D. Andersson, C. Stanek, T. Durakiewicz, J.L. Smith More than 65 years worth of unrelenting experimental and theoretical research on seemingly uncomplicated UO$_{2}$, a Mott-Hubbard insulator with well-localized 5$f-$electrons and a fluorite \textit{fcc} crystal structure, have not been able to elucidate some important questions such as the detailed nature of the low temperature AFM state, or the reasons behind unusual lattice properties that severely hinder the ability of this important nuclear material to transport heat. The high thermal conductivity shown by its non-magnetic counterpart, ThO$_{2}$, has hinted to the notion that unusual spin-lattice coupling is behind the crippled thermal behavior of UO$_{2}$. Here we present results of our thermodynamic investigations, on well-characterized and oriented single crystals$_{,\, }$focusing on fiber Bragg grating magnetostriction measurements in pulsed magnetic fields to 90T at the NHMFL PFF. Our data support a multidomain non-collinear 3-\textbf{k} AFM order below 30.8K, coupled to an oxygen-cage trigonal distortion that breaks time reversal symmetry. $^{\ast }$Work supported by the US DOE BES, Mat. Sci., and Eng. Div. The NHMFL PFF is supported by the NSF, the U.S. DOE., and the State of Florida through NSF coop. grant DMR-1157490. Work at LANL was supported by the U.S. DOE BES project "Science at 100 Tesla". [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y19.00007: Modulated magnetism in the ferromagnet PrPtAl : clear experimental evidence of the 'order by disorder' theory. J.-Ph. Reid, Chris O'Neill, Alex Walker, Calum Lithgow, Gino Abdul-Jabbar, Edward Yelland, Dmitry A. Sokolov, Andrew D. Huxley The ferromagnet PrPtAl is unlike any other. At the phase boundary between paramagnetism and ferromagnetism the fluctuations of the order parameter are so strong that energetically favourable phases of novel modulated magnetism emerge. In fact, it’s the lack of order (the ‘disorder’) that is pivotal to promote a new ‘order’. This mechanism is referred to as ‘order by disorder’ and is the centre of numerous theoretical studies [2,3]. In this seminar, following an introduction on the topic of ferromagnetic materials, I will show how we can use both electrical and thermal conductivities to learn everything about these phases of modulated magnetism and to validate the predictions of the ‘order by disorder’ theory. [1] G. Abdul-Jabbar et al. Nat. Phys. 11, 321–327 (2015). [2] G. J. Conduit et al. Phys. Rev. Lett. 103, 207201 (2009). [3] U. Karahasanovic et al. Phys. Rev. B 85, 165111 (2012). [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 12:51PM |
Y19.00008: Unexpected magnetism, and transport properties in mixed lanthanide compound. Arjun Pathak, Karl Gschneidner, Jr, Vitalij Pecharsky For intelligent materials design it is desirable to have compounds which have multiple functionalities such as a large magnetoresistance, ferromagnetic and ferrimagnetic states, and field-induced first-order metamagnetic transitions. Here, we discuss one such example where we have combined two lanthanide elements Pr and Er in Pr$_{\mathrm{0.6}}$Er$_{\mathrm{0.4}}$Al$_{\mathrm{2}}$. This compound exhibits multiple functionalities in magnetic fields between 1 and 40 kOe. It undergoes only a trivial ferrimagnetism to paramagnetism transition in a zero magnetic field, but Pr$_{\mathrm{0.6}}$Er$_{\mathrm{0.4}}$Al$_{\mathrm{2}}$ exhibits a large positive magnetoresistance (MR) for H$\ge $40 kOe, a small but non negligible negative MR for H$\le $30 kOe, and a clear Griffiths-like phase behavior at \textless 1 kOe. The compound also exhibits an asymmetry of hysteresis loop, or exchange bias (EB) effect after field cooling from the paramagnetic state. These phenomena are attributed to the competition between single-ion anisotropies of Pr and Er ions coupled with the opposite nearest-neighbor and next-nearest-neighbor exchange interactions. [Preview Abstract] |
Friday, March 18, 2016 12:51PM - 1:03PM |
Y19.00009: Magnetic and Metal-Insulator Transition in natural Transition Metal Sulfides Renxiong Wang, Tristin Metz, I-Lin Liu, Kefeng Wang, Xiangfeng Wang, J.R Jeffries, S.R. Saha, R.L. Greene, J. Paglione, C. C. Santelli, J, Post In collaboration with the Smithsonian Institution's National Museum of Natural History, we present detailed studies of a class of natural minerals with potential to harbor correlated behavior. Transition metal sulfide minerals, such as Bornite (Cu5FeS4), are an important family of compounds known for their thermoelectric properties. We will present low temperature experimental studies of magnetic transitions and focus on a compound that exhibits a metal to insulator transition concident with entrance to an antiferromagnetic ground state, suggesting a potentially interesting system with promise for realizing new correlated states of matter in a naturally occurring mineral. \newline [Preview Abstract] |
(Author Not Attending)
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Y19.00010: Emergent triangular structure in doped extended honeycomb Hubbard model Luca F. Tocchio, Ryui Kaneko, Roser Valenti, Federico Becca, Claudius Gros We investigate the extended honeycomb Hubbard model at $3/4$ filling. By using the mean-field approximation, we find a transition from a normal metal to a ferromagnetic metal at large Coulomb interaction $U$, and a transition to a charge ordered metal at large nearest-neighbor Coulomb interaction $V$. In the presence of both $U$ and $V$, we find a metal-insulator transition, where the insulating state possesses charge and magnetic orders. The charge rich sites are nearly fully occupied, while the charge poor sites form a triangular lattice at nearly half filling. We also apply the variational Monte Carlo method to take into account quantum fluctuations beyond the mean-field treatment, and find this charge ordered state to be stable at sufficiently large $U$ and $V$. [Preview Abstract] |
Friday, March 18, 2016 1:15PM - 1:27PM |
Y19.00011: Mechanisms of finite-temperature magnetism in the three-dimensional Hubbard model Daniel Hirschmeier, Hartmut Hafermann, Emanuel Gull, Alexander I. Lichtenstein, Andrey E. Antipov We examine the nature of the transition to the antiferromagnetically ordered state in the half-filled three-dimensional Hubbard model using the dual-fermion multiscale approach. Consistent with analytics, in the weak-coupling regime we find that spin-flip excitations across the Fermi surface are important, and that the strong coupling regime is described by Heisenberg physics. In the intermediate interaction, strong correlation regime we find aspects of both local and non-local correlations. We analyze the critical exponents of the transition in the strong coupling regime and find them to be consistent with Heisenberg physics down to an interaction of U/t=10. [Preview Abstract] |
Friday, March 18, 2016 1:27PM - 1:39PM |
Y19.00012: Quantum Monte Carlo study of magnetism in the Lieb Lattice Natanael Costa, Tiago Santos, Thereza Paiva, Raimundo dos Santos, Richard Scalettar The Hubbard model on the `Lieb lattice' provides an important example of how flat band systems may lead to ferromagnetism: at half filling Lieb proved that a ferrimagnetic ground state \emph{can} be achieved. Since a rigorous proof that long range order does indeed emerge is still lacking, here we report Determinant Quantum Monte Carlo (DQMC) simulations for this model. We found that the spin correlation between nearest neighbors are always antiferromagnetic, and that for small $U$ ferromagnetic long range order does set in in the ground state. However, spatial spin correlations weaken as $U$ is increased, and we established that long range order is suppressed above $U_{c} \approx 4.5$. We obtain the dependence of the magnetization with the on-site repulsion $U$, and show that it displays a maximum at $U\approx 3$. The behavior of the compressibility and of the double occupancy across this transition is also discussed. [Preview Abstract] |
Friday, March 18, 2016 1:39PM - 1:51PM |
Y19.00013: Using dephasing to distinguish composite and elementary particles Leonid P. Pryadko, Claudio Castelnovo, Mark I. Dykman, Roderich Moessner, Vadim N. Smelyanskiy Many-body topological excitations like domain walls in 1D can be treated quantum mechanically as particles. We establish limits on such a description in the presence of weak dephasing. Specifically, we compare dynamics of a particle in a tight-binding model with weak on-site dephasing, and that of a kink separating two locally distinguishable domains. In the latter case, dephasing rate of the off-diagonal matrix elements $\rho_{ab}$ of the density matrix is proportional to the distance $|a-b|$ from the diagonal, compared to a constant dephasing rate of such matrix elements for a single particle. We show that in a transport setting (quantum diffusion), with small density gradients, the dynamics of these two systems is nearly identical. The difference can only be seen when far off-diagonal matrix elements are important, as in the formation of a bound state, or in a two-path interferometer. We analyze the spectroscopic signature of a bound state of a domain wall, and suggest possible experimental signatures in spin chains. [Preview Abstract] |
Friday, March 18, 2016 1:51PM - 2:03PM |
Y19.00014: Spontaneous symmetry breaking in correlated wave functions Ryui Kaneko, Luca F. Tocchio, Roser Valenti, Federico Becca, Claudius Gros We show that Jastrow-Slater wave functions, in which a density-density Jastrow factor is applied onto an uncorrelated fermionic state, may possess long-range order even when all symmetries are preserved in the wave function. This fact is mainly related to the presence of a sufficiently strong Jastrow term (also including the case of full Gutzwiller projection, suitable for describing spin models). Selected examples are reported, including the spawning of N\'eel order and dimerization in spin systems, and the stabilization of density and orbital order in itinerant electronic systems. [1] Ryui Kaneko, Luca F. Tocchio, Roser Valent\'i, Federico Becca, and Claudius Gros, arXiv:1510.08653. [Preview Abstract] |
Friday, March 18, 2016 2:03PM - 2:15PM |
Y19.00015: On the magnetic structure and band gap of the double perovskite Ba2CuOsO6: Density functional analysis Changhoon Lee, Jisook Hong, Ji Hoon Shim, Myung-Hwan Whangbo The ordered double-perovskite Ba$_{2}$CuOsO$_{6}$, consisting of 3d and 5d transition-metal magnetic ions (Cu$^{2+}$ and Os$^{6+}$, respectively), is a magnetic insulator. It obeys the Curie-Weiss law with $\theta \quad =$ -13.3 K. We evaluated the spin exchange interactions of Ba$_{2}$CuOsO$_{6}$ by performing energy-mapping analysis based on DFT$+$U calculations and determined the band gap of Ba$_{2}$CuOsO$_{6}$ by DFT$+$U and DFT$+$U$+$SOC calculations. The antiferromagnetic ordering of Ba$_{2}$CuOsO$_{6}$ is due largely to the spin exchange interactions between Cu2$+$ ions, which are enhanced by the empty eg orbitals of the intervening Os$^{6+}$ ions. Both electron correlation and spin-orbit coupling are necessary to open a band gap for Ba$_{2}$CuOsO$_{6}$. [Preview Abstract] |
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