Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S29: Correlated Electron Magnetism I |
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Sponsoring Units: GMAG Chair: William Ratcliff, National Institute of Standards and Technology Room: 206A |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S29.00001: Investigation of magnetic order in Sm${Tr}$$_2$Zn$_{20}$ (${Tr}$ = Fe, Co, Ru) and Sm${Tr}$$_2$Cd$_{20}$ (${Tr}$ = Ni, Pd) Duygu Yazici, B. D. White, P.-C. Ho, N. Kanchanavatee, K. Huang, N. R. Dilley, M. B. Maple Single crystals of the cage compounds Sm${Tr}$$_2$Zn$_{20}$ (${Tr}$ = Fe, Co, Ru) and Sm${Tr}$$_2$Cd$_{20}$ (${Tr}$ = Ni, Pd) have been investigated by means of electrical resistivity, magnetization, and specific heat measurements. The compounds SmFe$_{2}$Zn$_{20}$, SmRu$_{2}$Zn$_{20}$, and SmNi$_{2}$Cd$_{20}$ exhibit ferromagnetic order with Curie temperatures of $T_C$ = 47.4 K, 7.6 K, and 7.5 K, respectively, whereas SmPd$_{2}$Cd$_{20}$ is an antiferromagnet with a N\'{e}el temperature of $T_N$ = 3.4 K. No evidence for magnetic order is observed in SmCo$_{2}$Zn$_{20}$ down to 110 mK. The Sommerfeld coefficients $\gamma$ are found to be 57 mJ/mol-K$^2$ for SmFe$_{2}$Zn$_{20}$, 79.5 mJ/mol-K$^2$ for SmCo$_{2}$Zn$_{20}$, 258 mJ/mol-K$^2$ for SmRu$_{2}$Zn$_{20}$, 165 mJ/mol-K$^2$ for SmNi$_{2}$Cd$_{20}$, and 208 mJ/mol-K$^2$ for SmPd$_{2}$Cd$_{20}$. Enhanced values of Sommerfeld coefficients $\gamma$ and a quadratic temperature dependence of the electrical resistivity at low temperature for SmRu$_{2}$Zn$_{20}$ and SmPd$_{2}$Cd$_{20}$ suggest an enhancement of the quasiparticle masses due to hybridization between localized 4$f$ and conduction electron states. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S29.00002: Non-Fermi liquid behavior and the undersceened Kondo effect in Fe$_{1-y}$Co$_{y}$Si Yan Wu, Brad Fulfer, Julia Chan, David Young, John DiTusa Mn or Co substitutions into the narrow band-gap insulator FeSi introduce charge carriers, either holes or electrons, accompanied by an equal density of more localized magnetic moments resulting in an interesting insulator-to-metal transition (IMT). Mn doping of FeSi exhibits an IMT where the nascent metal displays intriguing field sensitive non-Fermi-Liquid (NFL) behavior due to the undercompensation of $S=$1 impurity moments by the spin-1/2 hole carriers. Here, we present the results of an investigation of Fe$_{1-y}$Co$_{y}$Si ( 0$\le y\le $0.1). Our magnetization and susceptibility measurements indicate that for $y$\textless 0.03 Co-impurities alsointroduce a $S=$1 magnetic moment that have a tendency to form singlets whereas for larger $y$a ferromagnetic interaction that grows with $y$. We have discovered a NFLbehavior for $y$\textless 0.03 that evolves into the standard disordered Fermi-liquid form either by applying a magnetic field or by increasing $y$. The results of specific heat measurements on Fe$_{1-y}$Co$_{y}$Si,performed to explore the underlying underscreened Kondo mechanism, to investigate its variation with field and composition,and to compare with our Fe$_{1-x}$Mn$_{x}$Si data will be presented. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S29.00003: Kondo versus indirect exchange: the role of the lattice and the actual range of RKKY interactions in real materials Andrew Allerdt, Adrian Feiguin, Carlos Busser, George Martins Magnetic impurities embedded in a metal interact via an effective Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling mediated by the conduction electrons, which is commonly assumed to be long ranged, with an algebraic decay in the inter-impurity distance. However, they can also form a Kondo screened state that is oblivious to the presence of other impurities. We study the competition mechanisms between both effects on the square and cubic lattices by introducing an exact mapping onto an effective one-dimensional problem that we can solve with the density matrix renormalization group method (DMRG). We show a dramatic departure from the conventional RKKY theory, that can be attributed to the dimensionality and different densities of states, as well as the quantum nature of the magnetic moments. In particular, for dimension $d>1$, Kondo physics dominates even at short distances, while the ferromagnetic RKKY state is energetically unfavorable. Our findings can have clear implications in the interpretation of experiments and for tailoring the magnetic properties of surfaces. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 8:48AM |
S29.00004: Magnetism in CeRhIn$_5$ at high fields measured by NMR A. M. Mounce, F. Ronning, E. D. Bauer, J. D. Thompson, A. P. Reyes, P. L. Kuhns De Haas-van Alphen measurements[1] of CeRhIn$_5$ at ambient pressure show an abrupt change in the Fermi surface volume at high fields, $H^* \approx$ 30 T, and low temperatures resulting in antiferromagnetic phases with a small Fermi surface at fields below $H^*$ and a large Fermi surface at fields $H$ such that $H^* < H < 50$ T. Nuclear magnetic resonance (NMR) is the ideal probe for these magnetic states as the microscopic details are still lacking. Our preliminary NMR measurements find the magnetic order for $H\parallel c$ is incommensurate up to 30 T as opposed to $H \perp c$ which transitions from incommensurate to commensurate at $H \approx$ 2 T.[2] Furthermore, we find that the magnetic moment decreases near 17 T for $H \parallel c$. These measurements provide an insight into the magnetic anisotropy of CeRhIn$_5$ and are a crucial step to studying its high field phases. [1] L. Jiao et al., arXiv 1308.0294. [2] S. Raymond et al., J. Phys. Cond. Matt. 19, 242204 (2007). [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S29.00005: The Kondo Temperature of Two-dimensional Electron Gas with Rashba Spin-orbit Coupling Liang Chen, Jinhua Sun, Ho-Kin Tang, Hai-Qing Lin We use the Hirsch-Fye quantum Monte Carlo method to study the single magnetic impurity problem in two-dimensional electron gas with Rashba spin-orbit coupling. We calculate the spin susceptibilities for different spin-orbit couplings, different Hubbard interactions, and different chemical potentials. The Kondo temperatures for different parameters are estimated by fitting the universal curves of spin susceptibilities. We find that the Kondo temperature is almost a linear function of the Rashba spin-orbit energy when the chemical potential is close to the edge of the conduction band, and when the chemical potential is far away from the band edge, the Kondo temperature is independent of the spin-orbit coupling. These results demonstrate that, for single impurity problem in this system, the most important reason to alter the Kondo temperature is the divergence of density of states near the band edge, and the divergence is induced by the spin-orbit coupling. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S29.00006: Remarkably robust and correlated coherence and antiferromagnetism in (Ce$_{1-x}$La$_x$)Cu$_2$Ge$_2$ single crystals H. Hodovanets, S.L. Bud'ko, W.E. Straszheim, V. Taufour, E.D. Mun, H. Kim, P.C. Canfield We present results of transport and thermodynamic measurements on La diluted Kondo lattice compound CeCu$_2$Ge$_2$. La-substitution suppresses $T_N$ in an almost linear fashion from $\sim$ 4 K, for $x$ = 0, to below 0.36 K, for $x>$ 0.8. Curiously, the system also shows low temperature coherent scattering below $T_{coh}$ up to $\sim$ 0.9 of La, indicating a small percolation limit $\sim$ 9$\%$ of Ce that separates a coherent state from a single-ion Kondo impurity state. $T_{coh}$($H$) was found to have different functional dependencies in coherent and single-ion regimes. Surprisingly, $(T_{coh})^2$ was found to be proportional to $T_N$ over wide range of $x$. For Ce concentrations, $y=1-x$, in the range 0.01 $\leq y \leq$ 0.08, $T_{min}$ in the resistivity data is proportional to $y_{Ce}^{1/5}$ and field-dependent thermopower shows features as expected for the single-ion Kondo impurity. This work was supported by the Department of Energy, Basic Energy Sciences under Contract No. DE-AC02-07CH11358 and the AFOSR-MURI grant No. FA9550-09-1-0603. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S29.00007: Discovery of a 3d-transition-metal-based ferromagnetic Kondo lattice system Ahmad Us Saleheen, Tapas Samanta, Daniel Lepkowski, Alok Shankar, Joseph Prestigiacomo, Igor Dubenko, Abdiel Quetz, Roy McDougald Jr., Gregory McCandless, Julia Chan, Philip Adams, David Young, Naushad Ali, Shane Stadler The formation of a Kondo lattice results in a wide variety of exotic phenomena associated with the competition between the Kondo effect and the RKKY interaction, such as heavy fermions, non-Fermi liquid behavior, unconventional superconductivity, and so on. A quantum critical point (QCP) has been frequently observed at the boundaries of competing phases for antiferromagnetic materials. However, the existence of a ferromagnetic (FM) QCP is unclear. Moreover, FM Kondo lattices are rare. Here we report the discovery of a FM Kondo lattice system Mn$_{\mathrm{1-x}}$Fe$_{\mathrm{x}}$CoGe, which is the first example of a 3d-metal-based system (i.e., not rare-earth-based). Resistivity, magnetic susceptibility, heat capacity and thermopower studies on a single crystal sample indicate that the anisotropic FM kondo lattice has formed along c-axis. The signature of a spin density wave transition was also observed above the Kondo minimum, below which the resistivity follows a log(T) behavior. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S29.00008: Weak hybridization and isolated localized magnetic moments in the compounds CeT$_2$Cd$_{20}$ (T = Ni, Pd) Benjamin White, Duygu Yazici, Pei-Chun Ho, Noravee Kanchanavatee, Naveen Pouse, Aaron Friedman, M. Brian Maple Large Ce-Ce distances of 6.7-6.8~\AA~and weak hybridization between Ce 4$f$ and itinerant electron states act to promote stable localized magnetic moments in the compounds CeT$_2$Cd$_{20}$ (T = Ni, Pd), but also conspire to severely limit the strength of the Ruderman-Kittel-Kasuya-Yosida (RKKY) magnetic exchange interaction that couples them. As a consequence, measurements of electrical resistivity, performed on single-crystalline samples of these new Cd-based compounds down to 0.138 K, were unable to resolve any evidence for magnetic order. In this presentation, we will compare measurements of the physical properties of CeT$_2$Cd$_{20}$ (T = Ni, Pd) under ambient and applied pressures with the reported properties of the isostructural compounds CeT$_2$X$_{20}$ (T = transition metal; X = Al, Zn). We will use these comparisons to discuss the interplay of unit cell volume, hybridization, and the RKKY interaction and its role in establishing the ground states of the Ce-based ``1-2-20'' compounds. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S29.00009: Spin zero-point fluctuations in d-metals Vladimir Antropov, Andrey Kutepov, Kay Dewhurst, Sangeeta Sharma We analyze the structure and the strength of spin fluctuations at T=0 in pure metals: ferromagnetic 3d metals (Fe,Co,Ni) and paramagnetic Pd. The studies have been performed using obtained full tensor of generalized linear spin susceptibility in the density functional approach. Both real and imaginary frequencies integration with LAPW basis set have been implemented and tested for systems of different size. Our analysis is mainly focused on a decomposition of the fluctuating magnetic moment as a function of frequency and polarization near a point of magnetic instability. In addition we present the results when the external pressure and magnetic field applied. The obtained numbers have been incorporated into the traditional spin fluctuations theories. The spin fluctuation renormalization of mean field parameters has been found rather large and incompatible with the perturbation theory treatment. At the end we discuss the applicability of these theories for the analysis of real magnetic systems at low temperatures. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S29.00010: Itinerant magnetism in CaMn$_2$Al$_{10}$ Jack Simonson, Lucia Steinke, Shelby Zellman, Jedediah Kistner-Morris, Akshat Puri, Evon Andrews, Meigan Aronson We report the synthesis and basic properties of CaMn$_2$Al$_{10}$, a new itinerant magnet that is nearly isostructural with the known quantum critical compound YFe$_2$Al$_{10}$. Magnetic susceptibility measurements performed on single crystals reveal a cusp at 2 K. Electrical resistivity measurements similarly have a maximum at this temperature, and heat capacity measurements show a broad peak with total entropy of $\sim10\% R$ ln2. These results together with those of neutron diffraction measurements suggest that CaMn$_2$Al$_{10}$ is weakly magnetic and potentially close to a quantum critical point. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S29.00011: Complex magnetism and strong electronic correlations in Ce$_{2}$PdGe$_{3}$ Andrew Gallagher, Tiglet Besara, Jifeng Sun, Theo Siegrist, David Singh, Joe Thompson, Filip Ronning, Eric Bauer, Ryan Baumbach We report structure/chemical results, magnetization, heat capacity, and electrical transport data for single crystals of the new tetragonal compound Ce$_{2}$PdGe$_{3}$. Single crystal X-ray diffraction shows that this material crystallizes in the space group $P$42/\textit{mmc} -- and is related to the $\alpha $-ThSi$_{2}$-type structure. Complicated magnetism, with a two-part antiferromagnetic phase transition at $T_{\mathrm{N,1}} =$ 10.7 K and $T_{\mathrm{N,2}} =$ 9.6 K and subsequent ferromagnetic ordering near $T_{\mathrm{C}} \approx $ 2.25 K is observed. The ordered ground state emerges from a lattice of Ce ions that are hybridized with the conduction electrons, as revealed by the enhanced electronic coefficient of the specific heat $\gamma \approx $ 50 mJ/mol-Ce-K$^{2}$ (extrapolated to $T =$ 0 for $T$ \textless $T_{\mathrm{C}})$. Electronic structure calculations suggest that there is significant f-electron weight in the density of states near the Fermi energy, consistent with the enhanced specific heat, and that the Fermi surface includes sheets with distinct nesting vectors. We will discuss prospects for tuning the ferromagnetism to zero temperature to produce a ferromagnetic quantum phase transition: e.g., through applied pressure and/or chemical substitution. [Preview Abstract] |
(Author Not Attending)
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S29.00012: Transport and torque magnetometry measurements on CeAuSb$_{2}$ Lishan Zhao, Edward Yelland, Jan Bruin, Hide Sakai, Ilya Sheikin, Andrew Mackenzie The tetragonal crystal CeAuSb$_{2}$ has a layered structure and orders antiferromagnetically at T $\sim$ 6K. Under a c-axis magnetic field, the Neel temperature is gradually suppressed to zero at a possible field-tuned quantum critical point at about 6 T. Within this antiferromagnetic phase, between the QCP and about 2.8 T, there is an additional, novel phase. We report transport measurements on pure single crystals of CeAuSb$_{2}$, in fields of up to 35 T and from room temperature down to 100 mK. We also report torque magnetometry measurements. Unlike a recent report, we find single, sharp transitions into the novel phase. We discuss the nature of the novel phase.\\[4pt] The work presented is supported by TOPNES(Topological Protection and Non-Equilibrium States in Strongly Correlated Electron Systems research programme), the Engineering and Physical Sciences Research Council (EPSRC, UK) and Max Planck Institute for Chemical Physics of Solids(Dresden, Germany) etc. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S29.00013: Effects of uni-axial strain on electronic nematic state in Sr$_{3}$Ru$_{2}$O$_{7}$ Daniel Brodsky, Mark Barber, Clifford Hicks, Robin Perry, Andrew Mackenzie Sr$_{3}$Ru$_{2}$O$_{7}$ exhibits a novel electronic phase in the vicinity of a magnetic field-tuned quantum critical point. This phase shows strong anisotropy under weak symmetry-breaking fields, so it is thought to be intrinsically nematic. We study this phase under anisotropic strain, using a piezoelectric-based device that can both compress and tension samples. We find that the phase responds strongly to anisotropic strain, and discuss this result in the context of various theoretical models for the phase. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S29.00014: Evidence of magnetic clusters in the disordered ferromagnet Ni-V close to the quantum critical concentration Ruizhe Wang, S. Ubaid-Kassis, A. Schroeder, P.J. Baker, F.L. Pratt, S.J. Blundell, T. Lancaster, I. Franke, J.S. Moeller, T. Vojta We report the results of muon spin relaxation ($\mu$SR) experiments in zero field (ZF) and transverse field (TF) as well as magnetization (M) data of Ni$_{1-x}$V$_{x}$ close to the critical vanadium concentration $x_c \approx11.6\%$ where the onset of the ferromagnetic (FM) order is suppressed. This material features a prototypical disordered quantum phase transition (QPT) as seen in the temperature (T) and magnetic field (H) dependence of $M(H,T)$. In the paramagnetic phase (PM) above $x_c$, $M(H,T)$ is well described by non-universal power laws characterized by an exponent $\alpha(x-x_c)$, establishing a quantum Griffiths phase. Here, we focus on the FM side of the QPT below $x_c$. After subtracting the spontaneous magnetization $M_0$, we find that $M(H,T)-M_0$ also follows a power law in $H$ at low $T$ with an analogous non-universal exponent $\alpha(x_c-x)$. This is the first evidence of a quantum Griffiths phase within the FM phase in this disordered alloy. $\mu$SR in ZF recognized a broad field distribution below $x_c$ as evidence of magnetic spatial inhomogeneities in the FM phase. Different muon depolarization rates in TF and ZF reveal magnetic clusters already in the PM regime. These observed clusters are important generic ingredients of a disordered QPT. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S29.00015: CeCu$_{2}$Ge$_{2}$: Challenging our understanding of quantum criticality Bin Zeng, Qiu Zhang, Daniel Rhodes, Yasuyuki Shimura, Daiki Watanabe, Ryan Baumbach, Pedro Schlottmann, Takao Ebihara, Luis Balicas Here, we unveil evidence for a quantum phase transition in CeCu$_{2}$Ge$_{2}$. For the H//c-axis, no experimental evidence for QC. But as H is rotated towards the a-axis, these $\mu $'s increase considerably becoming undetectable for $\theta $ \textgreater 56$^{\circ}$. Around H$\sim $ 30 T the resistivity becomes $\propto $T which, coupled to the divergence of $\mu $, indicates the existence of a field-induced QC point(T $=$ 0 K). This observation, suggesting FS hot spots associated with the SDW nesting vector, is at odds with current QC scenarios for which the continuous suppression of all relevant energy scales at H$_{\mathrm{p}}(\theta $,T ) should lead to a line of quantum-critical points in the H-$\theta $ plane. Finally, we show that the complexity of its magnetic phase diagram(s) makes CeCu$_{2}$Ge$_{2}$ an ideal system to explore field-induced quantum tricritical and QC end points. [Preview Abstract] |
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