Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S20: Correlated Electron Magnetism |
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Sponsoring Units: DCMP GMAG Chair: Ryan Baumbach, National High Magnetic Field Laboratory Room: 280 |
Thursday, March 16, 2017 11:15AM - 11:27AM |
S20.00001: Quantum Oscillations in FeAs in the Spin Density Wave State Daniel Campbell, David Parker, Chris Eckberg, Kefeng Wang, Dave Graf, Johnpierre Paglione Binary FeAs orders in a spin density wave (SDW) state at temperatures below TN $=$ 70 K, much like the iron pnictides and isostructural pressure-induced superconductors CrAs and MnP, making it an ideal system with which to study the relationship between spin-density wave magnetism and superconductivity. We will present a new single-crystal flux growth technique that produces the highest quality specimens to date and allows for the observation of quantum oscillations in high-field torque measurements. Analyzing the dependence of oscillation frequency and amplitude on temperatures and field angles, we will review the effective electron and hole carrier masses and Fermi surface geometry in the SDW state and compare to theoretical calculations. [Preview Abstract] |
Thursday, March 16, 2017 11:27AM - 11:39AM |
S20.00002: Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2 Andrew May, Stuart Calder, David Parker, Brian Sales, Michael McGuire CuFe$_{\mathrm{2}}$Ge$_{\mathrm{2}}$ has been identified as a system with competing magnetic ground states that are strongly coupled to the crystal lattice and easily manipulated by temperature or applied magnetic field. Powder neutron diffraction data reveal the emergence of antiferromagnetic (AFM) order near $T_{\mathrm{N\thinspace }}=$ 175 K, as well as a transition into an incommensurate AFM spin structure below approximately 125 K. Together with refined moments of approximately 1 Bohr magneton per iron, the incommensurate structure supports an itinerant picture of magnetism in CuFe$_{\mathrm{2}}$Ge$_{\mathrm{2}}$, which is consistent with theoretical calculations. Bulk magnetization measurements suggest that the spin structures are easily manipulated with an applied field, which further demonstrates the near-degeneracy of different magnetic configurations. Interestingly, the thermal expansion is found to be very anisotropic, and the $c$ lattice parameter has anomalous temperature dependence near $T_{\mathrm{N}}$. These results show that the ground state of CuFe$_{\mathrm{2}}$Ge$_{\mathrm{2}}$ is easily manipulated by external forces, making it a potential parent compound for a rich phase diagram of emergent phenomena. [Preview Abstract] |
Thursday, March 16, 2017 11:39AM - 11:51AM |
S20.00003: The Effects of Nickel Substitution on Ferromagnetism in Fe$_3$GeTe$_2$ Layered Structured Compound Gil Drachuck, Morgan W. Masters, Valentin Taufour, Tej N. Lamichhane, Qisheng Ling, Sergey L. Bud'ko, Paul C. Canfield We have grown a series of nickel substituted single crystals of the layered structured ferromagnet Fe$_3$GeTe$_2$. The crystals were characterized with single crystal X-ray diffraction, magnetic susceptibility, magnetization under pressure, electrical resistivity and Mossbauer spectroscopy. We will report the changes in the ferromagnetic transition temperature, ordered magnetic moment size, Curie-Weiss temperature and the crystallographic and magnetic structure, as a result of the nickel substitution. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:03PM |
S20.00004: Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe$_4$ Na Hyun Jo, Yun Wu, Daixiang Mou, Lunan Huang, Valentin Taufour, Adam Kaminski, Sergey Bud'ko, Paul Canfield Systematic measurements of temperature dependent magnetization, resistivity and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe$_4$. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic $c$-axis below $T_\textrm{N}$ = 255\,K. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Neel temperature decreases monotonically under pressure, down to $T_\textrm{N}$ = 236\,K at 5.22\,GPa. The pressure dependence of transport properties show anomalies near 2\,GPa suggesting that there is a phase transition (structural, magnetic, and/or electronic) induced by pressure. For pressures higher than 2\,GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states. [Preview Abstract] |
Thursday, March 16, 2017 12:03PM - 12:15PM |
S20.00005: Tricritical wings in itinerant ferromagnet LaCrGe3 under pressure Udhara Kaluarachchi, Sergey Bud'ko, Paul Canfield, Valentin Taufour In ferromagnetic systems, quantum criticality is avoided either by a change of the transition order, becoming of the first order at a tricritical point (TCP), or by the appearance of modulated magnetic phases. In the first case, for pressures above TCP, application of magnetic field reveals the wing structure phase diagram in $T$-$p$-$H$ space. In the case where the transition leads to modulated magnetic phase, no wing structure phase diagram has been reported so far. Recent pressure study on ferromagnetic LaCrGe$_3$ revealed that the paramagnetic-ferromagnetic quantum critical point is avoided by the appearance of a modulated magnetic phase\footnote{Taufour {\it et al.} Phys. Rev. Lett. \textbf{117}, 037207 (2016)}. We will present the constructed $T$-$p$-$H$ phase diagram of LaCrGe$_3$ via electrical resistivity measurement and discuss a new possibility where tricritical wings appear in addition to the modulated magnetic phase. [Preview Abstract] |
Thursday, March 16, 2017 12:15PM - 12:27PM |
S20.00006: Torque magnetometry and magnetocalorimetry study of meatamagnetic transition in CeAuBi$_2$ single crystals H. Hodovanets, H. Kim, C. J. Eckberg, J. Paglione CeAuBi$_2$ is a highly anisotropic heavy-fermion antiferromagnet that develops a long-range order near 13 K that gets suppressed to zero temperature near a critical magnetic field of 75 kOe. Based on several thermodynamic measurements, a first-order spin-flop transition is observed at this critical field below a tricritical point at \textit{T} $\sim$ 6 K, and several other features follow a continuous trend as a function of magnetic field through this region. Here, we study CeAuBi2 single crystals with torque magnetometry and magnetocalorimetry to further explore its magnetic anisotropy and the evolution of the ground state with application of magnetic field. [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 12:39PM |
S20.00007: Strain-Induced Antiferromagnetic Phase in CeAuSb$_2$ Joonbum Park, Hideaki Sakai, Andrew Mackenzie, Clifford Hicks We present results of the electrical transport measurements under uniaxial pressure on the antiferromagnet CeAuSb$_2$. In the unstrained system, the resistivity along [100] shows a sharp drop at the N$\acute{\rm e}$el temperature ($T$${\rm_N} \approx$ 6.5 K), suggesting a first order transition. With compression along [100] by $\approx$ 0.3 $\%$, the transition splits into two continuous transitions, at temperatures $T_{1}$ and $T_{2}$. $T_{1}$ is fully suppressed at a compression of $\approx$ 0.6 $\%$, and in pressure ramps at low temperature this transition is a sharp cusp with hysteresis, indicating a first-order transition. $T_{2}$, on the other hand, rises continuously with increasing compression, reaching 9 K at 1.2 $\%$ compression. At present, the nature of the strain-induced phase between $T_{1}$ and $T_{2}$ is not clear. [Preview Abstract] |
Thursday, March 16, 2017 12:39PM - 12:51PM |
S20.00008: Discovery and Characterization of Single Crystalline $R_{5}$Co$_{2}$Ge$_{3}$ ($R$ = Ce-Nd, Sm) S. M. Saunders$^{a,b}$, Q. Lin$^a$, T. Kong$^{a,b}$, G. J. Miller$^{a,c}$, S. L. Bud'ko$^{a,b}$, P. C. Canfield$^{a,b}$ Single crystalline $R_{5}$Co$_{2}$Ge$_{3}$ ($R$ = Ce-Nd, Sm) were synthesized through flux-based crystal growth methods. In this work we analyze powder x-ray diffraction, electrical resistivity, magnetization, and specific heat of various members of the $R_{5}$Co$_{2}$Ge$_{3}$ family. We observe characteristic Lanthanide contraction as we increase 4f electron concentration. Magnetization measurements show an increase of transition temperature from $T_\textrm{c}$=6~K for Ce$_{5}$Co$_{2}$Ge$_{3}$ to $T_\textrm{N}$=220~K for Sm$_{5}$Co$_{2}$Ge$_{3}$, as well as other magnetic transitions upon change in temperature for various members of the family. The inferred effective moment is larger than expected from pure 4f electron contribution, suggesting contribution to the magnetization from Co in the system. Specific heat and electrical resistivity confirm the transition temperatures of the $R_{5}$Co$_{2}$Ge$_{3}$ series. [Preview Abstract] |
Thursday, March 16, 2017 12:51PM - 1:03PM |
S20.00009: The influence of hydrostatic pressure on the meta-magnetic transition and magnetocaloric properties of DyRu$_{\mathrm{2}}$Si$_{\mathrm{2}}$. Ahmad Ikhwan Us Saleheen, Tapas Samanta, Mojammel Khan, Igor Dubenko, Philip Adams, David Young, Naushad Ali, Shane Stadler We have studied the magnetic and magnetocaloric properties of the tetragonal rare-earth compound DyRu$_{\mathrm{2}}$Si$_{\mathrm{2}}$ as a function of applied hydrostatic pressure. At atmospheric pressure, transitions were observed at T$_{\mathrm{t}} \quad =$ 3.4 K and T$_{\mathrm{N}} \quad =$ 29.2 K. The isothermal entropy change ($\Delta $S) and the adiabatic temperature change ($\Delta $T$_{\mathrm{ad}})$ were calculated from magnetization data collected at different applied pressures and from heat capacity measurements conducted at atmospheric pressure, respectively. A suppression of the magnetization was observed for P $=$ 0.588 GPa and P $=$ 0.654 GPa . Multi-step meta-magnetic-transitions as were observed at atmospheric pressure, were not present at these pressure values. For P $\approx $ 1 GPa, the saturation magnetization increased, and the multi-step meta-magnetic transitions reappeared. This trend of pressure dependence was also apparent in the isothermal entropy change ($\Delta $S) versus temperature (T) curves. Using a Maxwell relation, we estimated the volume magnetostriction from the pressure dependent magnetization measurements. [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S20.00010: Magnetic field driven magnetic domain motion on high anisotropy $UMn_2Ge_2$ Xinzhou Tan, Alex de Lozanne, Morgann Berg, Ryan E. Baumbach, Eric D. Bauer, Joe D. Thompson, Filip Ronning The ternary intermetallic $UMn_2Ge_2$ ferromagnet has a tetragonal crystal structure of type $ThCr_2Si_2$. It has been long reported that local U and Mn moments in $UMn_2Ge_2$ order on their respective sublattices at temperatures near 100 and 380 K. A more recent report also showed this compound exhibits huge uniaxial magnetocrystalline anisotropy in a pulsed experiment with magnetic fields up to 62 T. Our previous results obtained using magnetic force microscopy (MFM) indeed confirmed that $UMn_2Ge_2$ displays uniaxial anisotropy. We observed that branching magnetic domains on surface of the sample form flower-like patterns and stay unchanged from 77 K up to room temperature in zero magnetic field. We are currently investigating field-driven motions of the surface magnetic domains of $UMn_2Ge_2$ under magnetic fields up to 8 T at various temperatures. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S20.00011: Novel Magnetic and Transport Properties of UAu0.66Sb2 Single Crystal Wen Zhang, Chun-Yu Guo, Dong-Hua Xie, Yi Liu, Shi-Yong Tan, Wei Feng, Xie-Gang Zhu, Qin Liu, Y. Z. Zhang, Yun Zhang, Li-Zhu Luo, Hui-Qiu Yun, Xin-Chun Lai Replace this text with your abstract body. We have successfully synthesized single crystals of UAu$_{\mathrm{0.66}}$Sb$_{\mathrm{2}}$ using a flux method and present a comprehensive study of the physical properties using magnetic susceptibility, electrical resistivity and specific heat measurements. UAu$_{\mathrm{0.66}}$Sb$_{\mathrm{2\thinspace }}$compound undergoes an antiferromagnetic transition at 71 K followed by a possible ferromagnetic transition below 30 K. The easy axis of magnetization is along the $c $axis. Two first-order meta-magnetic transitions and a magnetization plateau at$ M \approx \quad M_{\mathrm{max}}$/3 are observed and analyzed. The magnetization plateau at $M \approx \quad M_{\mathrm{max}}$/3 may result from two sublattice magnetization in UAu$_{\mathrm{0.66}}$Sb$_{\mathrm{2}}$. We map the field-temperature phase diagram for fields applied parallel to the easy magnetization \quad axis. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S20.00012: Magnetic and transport properties of f-site depleted Periodic Anderson Model Natanael Costa, Maykon Araujo, Jose de Lima, Thereza Paiva, Raimundo Santos, Richard Scalettar We will discuss Determinant Quantum Monte Carlo simulations for the Periodic Anderson Model on a square lattice in which the strongly correlated f-sites are depleted. When the depletion is random, the model is relevant to the magnetic properties of heavy fermion materials doped with non-magnetic ions. Here we investigate both random and non-random removal of f sites in order to get better insight into which of the effects of doping are due to disorder, and which are generic to any sort of site removal. We present results first for a single depletion, i.e. a Kondo-Hole, show how local singlets around the depleted site are broken, and the resulting effects on the magnetic susceptibility. When more sites are depleted, we provide evidence long range magnetic ordering can be induced. Our analyses for depletion of half the sites probes the existence of ferromagnetic long range order for both small and large values of hybridization. The examination of magnetic sublattice correlation functions provides evidence that magnetism is not entirely due to the remaining f-sites, but there is also a contribution from the weakly correlated c-electrons on the depleted sites. This research is supported by the Dept. of Energy grant number DE-NA0002908, and Brazilian agencies FAPERJ, FAPEPI and CNPq. [Preview Abstract] |
Thursday, March 16, 2017 1:39PM - 1:51PM |
S20.00013: Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application to UO$_2$ Nicola Lanata, Yongxin Yao, Xiaoyu Deng, Vladimir Dobrosavljević, Gabriel Kotliar We derive an exact operatorial reformulation of the rotational invariant slave boson method and we apply it to describe the orbital differentiation in strongly correlated electron systems starting from first principles. The approach enables us to treat strong electron correlations, spin-orbit coupling and crystal field splittings on the same footing by exploiting the gauge invariance of the mean-field equations. We apply our theory to the archetypical nuclear fuel UO$_2$, and show that the ground state of this system displays a pronounced orbital differention within the $5f$ manifold, with Mott localized $\Gamma_8$ and extended $\Gamma_7$ electrons. [Preview Abstract] |
Thursday, March 16, 2017 1:51PM - 2:03PM |
S20.00014: Periodic Anderson model with Holstein phonons for the description of the Cerium volume collapse Enzhi Li, Ka-Ming Tam, Juana Moreno, Mark Jarrell The volume collapse transition of Cerium has intrigued physicists since its discovery several decades ago. Various models and mechanisms have been proposed, the most prominent scenarios are based on the Mott transition and the Kondo volume collapse transition. In this study, we explore the volume collapse by a dynamical mean field theory (DMFT) study of the periodic Anderson model with phonons in the conduction band. This allows us to study the effect of the electron-phonon interaction on the volume collapse. In order to faithfully account for the volume collapse, we also include the effects due to the volume and temperature dependent bulk modulus. We find that as the electron-phonon interaction strength increases, the volume collapse effect is enhanced, which is consistent with the suggestion that the phonons have an important contribution in the volume collapse transition. Although we start with the canonical model for the Kondo volume collapse scenario, our results have some of the characteristics of the Mott scenario. [Preview Abstract] |
Thursday, March 16, 2017 2:03PM - 2:15PM |
S20.00015: Constraints on the Fermi liquid scaling of the optical conductivity in MnSi J. Steven Dodge, Laleh Mohtashemi, Michael Bartram, Amir Farahani, Eric Karhu, Theodore L. Monchesky We will present time-domain terahertz spectroscopy measurements of the optical conductivity of MnSi thin films. The measurements cover a temperature range $T = $ 5--300 K and a frequency range $\nu =$ 0.1--4.0 THz, with high accuracy and precision. Below $T\approx 35$ K and $\nu \approx 2$ THz, the conductivity is consistent with the prediction of Fermi-liquid theory, $\rho(\omega,T) = [\sigma(\omega,T)]^{-1} = \rho_0 + A[(\hbar\omega)^2 + (p\pi k_B T)^2]$, with $p=2$. We observe deviations from this scaling at higher frequencies and temperatures, which allows us to establish the boundary of the Fermi-liquid scaling regime. As the temperature increases further, the system loses quasi-particle coherence, while the plasma frequency inferred from a Drude fit decreases dramatically. [Preview Abstract] |
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