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Li Y, Phelan D, Ye F, Zheng H, Krivyakina E, Samarakoon A, LaBarre PG, Neu J, Siegrist T, Rosenkranz S, Syzranov SV, Ramirez AP. Evolution of magnetic surfboards and spin glass behavior in (Fe 1-pGa p) 2TiO 5. J Phys Condens Matter 2023; 35:475401. [PMID: 37557895 DOI: 10.1088/1361-648x/aceede] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Accepted: 08/09/2023] [Indexed: 08/11/2023]
Abstract
The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe2TiO5has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility (χ) and specific heat data (C) for Fe2TiO5diluted with non-magnetic Ga, (Fe1-pGap)2TiO5, for disorder parameterp= 0, 0.11, and 0.42, and elastic neutron scattering data forp= 0.20. A uniform suppression ofTgis observed upon increasingp, along with a value ofχTgthat increases asTgdecreases, i.e.dχ(Tg)/dTg<0We also observeCT∝T2in the low temperature limit. The observed behavior places (Fe1-pGap)2TiO5in the category of a strongly geometrically frustrated SG.
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Affiliation(s)
- Y Li
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
| | - D Phelan
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
| | - F Ye
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States of America
| | - H Zheng
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
| | - E Krivyakina
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
- Department of Physics, Northern Illinois University, DeKalb, IL 60115, United States of America
| | - A Samarakoon
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
| | - P G LaBarre
- Physics Department, University of California Santa Cruz, Santa Cruz, CA 95064, United States of America
| | - J Neu
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, United States of America
- Nuclear Nonproliferation Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States of America
| | - T Siegrist
- National High Magnetic Field Laboratory, Tallahassee, FL 32310, United States of America
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, FL 32310, United States of America
| | - S Rosenkranz
- Materials Science Division, Argonne National Laboratory, Lemont, IL 60439, United States of America
| | - S V Syzranov
- Physics Department, University of California Santa Cruz, Santa Cruz, CA 95064, United States of America
| | - A P Ramirez
- Physics Department, University of California Santa Cruz, Santa Cruz, CA 95064, United States of America
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LaBarre PG, Rydh A, Palmer-Fortune J, Frothingham JA, Hannahs ST, Ramirez AP, Fortune NA. Magnetoquantum oscillations in the specific heat of a topological Kondo insulator. J Phys Condens Matter 2022; 34:36LT01. [PMID: 35767985 DOI: 10.1088/1361-648x/ac7d2b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 06/29/2022] [Indexed: 06/15/2023]
Abstract
Surprisingly, magnetoquantum oscillations (MQOs) characteristic of a metal with a Fermi surface have been observed in measurements of the topological Kondo insulator SmB6. As these MQO have only been observed in measurements of magnetic torque (dHvA) and not in measurements of magnetoresistance (SdH), a debate has arisen as to whether the MQO are an extrinsic effect arising from rare-earth impurities, defects, and/or aluminum inclusions or an intrinsic effect revealing the existence of charge-neutral excitations. We report here the first observation of MQO in the low-temperature specific heat of SmB6. The observed frequencies and their angular dependence for these flux-grown samples are consistent with previous results based on magnetic torque for SmB6but the inferred effective masses are significantly larger than previously reported. Such oscillations can only be observed if the MQO are of bulk thermodynamic origin; the measured magnetic-field dependent oscillation amplitude and effective mass allow us to rule out suggestions of an extrinsic, aluminum inclusion-based origin for the MQO.
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Affiliation(s)
- P G LaBarre
- Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, United States of America
| | - A Rydh
- Department of Physics, Stockholm University, Stockholm, SE-106 91, Sweden
| | - J Palmer-Fortune
- Department of Physics, Smith College, Northampton, MA 01063, United States of America
| | - J A Frothingham
- Department of Physics, Smith College, Northampton, MA 01063, United States of America
| | - S T Hannahs
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310-3706, United States of America
| | - A P Ramirez
- Department of Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, United States of America
| | - N A Fortune
- Department of Physics, Smith College, Northampton, MA 01063, United States of America
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Syzranov SV, Ramirez AP. Eminuscent phase in frustrated magnets: a challenge to quantum spin liquids. Nat Commun 2022; 13:2993. [PMID: 35637214 PMCID: PMC9151641 DOI: 10.1038/s41467-022-30739-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 05/16/2022] [Indexed: 12/04/2022] Open
Abstract
A geometrically frustrated (GF) magnet consists of localised magnetic moments, spins, whose orientation cannot be arranged to simultaneously minimise their interaction energies. Such materials may host novel fascinating phases of matter, such as fluid-like states called quantum spin-liquids. GF magnets have, like all solid-state systems, randomly located impurities whose magnetic moments may “freeze” at low temperatures, making the system enter a spin-glass state. We analyse the available data for spin-glass transitions in GF materials and find a surprising trend: the glass-transition temperature grows with decreasing impurity concentration and reaches a finite value in the impurity-free limit at a previously unidentified, “hidden”, energy scale. We propose a scenario in which the interplay of interactions and entropy leads to a crossover in the permeability of the medium that assists glass freezing at low temperatures. This low-temperature, “eminuscent”, phase may obscure or even destroy the widely-sought spin-liquid states in rather clean systems. A spin-glass forms in frustrated magnetic systems when at low temperatures impurity sites “freeze” into a random spin configuration. Here, by looking back at previous experimental results, Syzranov and Ramirez show that the glass-transition temperature grows with decreasing impurity concentration.
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LaBarre PG, Kuthanazhi B, Abel C, Canfield PC, Ramirez AP. Extremely Weakly Interacting ΔS_{z}=0 and ΔS_{z}=1 Excitations and Evidence for Fractional Quantization in a Magnetization Plateau: CeSb. Phys Rev Lett 2020; 125:247203. [PMID: 33412048 DOI: 10.1103/physrevlett.125.247203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 10/22/2020] [Accepted: 10/23/2020] [Indexed: 06/12/2023]
Abstract
The plateau at 1/3 of the saturation magnetization M_{s} in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured M and the specific heat C in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with ΔS_{z}=1 as measured by M, coexist with a much larger population of ΔS_{z}=0 excitations measured by C but invisible to M. The large density of ΔS_{z}=0 excitations, their energy gap, and their seeming lack of interaction with ΔS_{z}=1 excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in M(H) are seen, the size of which, 0.15%M_{s}, is consistent with fractional quantization of magnetization per site in the down-spin layers.
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Affiliation(s)
- P G LaBarre
- Department of Physics, University of California Santa Cruz, Santa Cruz, California 95064, USA
| | - B Kuthanazhi
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
- Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
| | - C Abel
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
- Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
| | - P C Canfield
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
- Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
| | - A P Ramirez
- Department of Physics, University of California Santa Cruz, Santa Cruz, California 95064, USA
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LaBarre PG, Dong L, Trinh J, Siegrist T, Ramirez AP. Evidence for undoped Weyl semimetal charge transport in Y 2Ir 2O 7. J Phys Condens Matter 2020; 32:02LT01. [PMID: 31581141 DOI: 10.1088/1361-648x/ab4aaf] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Weyl fermions scattering from a random Coulomb potential are predicted to exhibit resistivity versus temperature [Formula: see text] in a single particle model. Here we show that, in closed-environment-grown polycrystalline samples of Y2Ir2O7, [Formula: see text] over four orders of magnitude in [Formula: see text]. While the measured prefactor, [Formula: see text], is obtained from the model using reasonable materials parameters, the [Formula: see text] behavior extends far beyond the model's range of applicability. In particular, the behavior extends into the low-temperature, high-resistivity region where the Ioffe-Regel parameter, [Formula: see text]. Strong on-site Coulomb correlations, instrumental for predicting a Weyl semimetal state in Y2Ir2O7, are the possible origin of such 'bad' Weyl semimetal behavior.
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Affiliation(s)
- P G LaBarre
- Physics Department, University of California Santa Cruz, Santa Cruz, CA 95064, United States of America
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Giraldo S, Ramirez AP, Flórez E, Acelas NY. Adsorbent materials obtained from palm waste and its potential use for contaminants removal from aqueous solutions. ACTA ACUST UNITED AC 2019. [DOI: 10.1088/1742-6596/1386/1/012036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Wallace MK, LaBarre PG, Li J, Pi ST, Pickett WE, Dessau DS, Haskel D, Ramirez AP, Subramanian MA. Local Moment Instability of Os in Honeycomb Li 2.15Os 0.85O 3. Sci Rep 2018; 8:6605. [PMID: 29700362 PMCID: PMC5919924 DOI: 10.1038/s41598-018-25028-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 04/13/2018] [Indexed: 11/10/2022] Open
Abstract
Compounds with honeycomb structures occupied by strong spin orbit coupled (SOC) moments are considered to be candidate Kitaev quantum spin liquids. Here we present the first example of Os on a honeycomb structure, Li2.15(3)Os0.85(3)O3 (C2/c, a = 5.09 Å, b = 8.81 Å, c = 9.83 Å, β = 99.3°). Neutron diffraction shows large site disorder in the honeycomb layer and X-ray absorption spectroscopy indicates a valence state of Os (4.7 ± 0.2), consistent with the nominal concentration. We observe a transport band gap of Δ = 243 ± 23 meV, a large van Vleck susceptibility, and an effective moment of 0.85 μB, much lower than expected from 70% Os(+5). No evidence of long range order is found above 0.10 K but a spin glass-like peak in ac-susceptibility is observed at 0.5 K. The specific heat displays an impurity spin contribution in addition to a power law ∝T(0.63±0.06). Applied density functional theory (DFT) leads to a reduced moment, suggesting incipient itineracy of the valence electrons, and finding evidence that Li over stoichiometry leads to Os(4+)−Os(5+) mixed valence. This local picture is discussed in light of the site disorder and a possible underlying quantum spin liquid state.
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Affiliation(s)
- M K Wallace
- Department of Chemistry, Oregon State University, Corvallis, OR, 97331, USA
| | - P G LaBarre
- Department of Physics, University of California Santa Cruz, Santa Cruz, CA, 95064, USA
| | - Jun Li
- Department of Chemistry, Oregon State University, Corvallis, OR, 97331, USA
| | - S-T Pi
- Department of Physics, University of California Davis, Davis, CA, 95616, USA
| | - W E Pickett
- Department of Physics, University of California Davis, Davis, CA, 95616, USA
| | - D S Dessau
- Department of Physics, University of Colorado, Denver, CO, 80309, USA
| | - D Haskel
- Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - A P Ramirez
- Department of Physics, University of California Santa Cruz, Santa Cruz, CA, 95064, USA
| | - M A Subramanian
- Department of Chemistry, Oregon State University, Corvallis, OR, 97331, USA.
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Dun ZL, Trinh J, Li K, Lee M, Chen KW, Baumbach R, Hu YF, Wang YX, Choi ES, Shastry BS, Ramirez AP, Zhou HD. Magnetic Ground States of the Rare-Earth Tripod Kagome Lattice Mg_{2}RE_{3}Sb_{3}O_{14} (RE=Gd,Dy,Er). Phys Rev Lett 2016; 116:157201. [PMID: 27127982 DOI: 10.1103/physrevlett.116.157201] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Indexed: 06/05/2023]
Abstract
We present the structural and magnetic properties of a new compound family, Mg_{2}RE_{3}Sb_{3}O_{14} (RE=Gd,Dy,Er), with a hitherto unstudied frustrating lattice, the "tripod kagome" structure. Susceptibility (ac, dc) and specific heat exhibit features that are understood within a simple Luttinger-Tisza-type theory. For RE=Gd, we found long-ranged order (LRO) at 1.65 K, which is consistent with a 120° structure, demonstrating the importance of diople interactions for this 2D Heisenberg system. For RE=Dy, LRO at 0.37 K is related to the "kagome spin ice" physics for a 2D system. This result shows that the tripod kagome structure accelerates the transition to LRO predicted for the related pyrochlore systems. For RE=Er, two transitions, at 80 mK and 2.1 K are observed, suggesting the importance of quantum fluctuations for this putative XY system.
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Affiliation(s)
- Z L Dun
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA
| | - J Trinh
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - K Li
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China
- Center for High Pressure Science and Technology Advanced Research, Beijing 100094, People's Republic of China
| | - M Lee
- Department of Physics, Florida State University, Tallahassee, Florida 32306-3016, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA
| | - K W Chen
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA
| | - R Baumbach
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA
| | - Y F Hu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China
| | - Y X Wang
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People's Republic of China
| | - E S Choi
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA
| | - B S Shastry
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - A P Ramirez
- Department of Physics, University of California, Santa Cruz, California 95064, USA
| | - H D Zhou
- Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310-3706, USA
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LaForge AD, Pulido SH, Cava RJ, Chan BC, Ramirez AP. Quasispin glass in a geometrically frustrated magnet. Phys Rev Lett 2013; 110:017203. [PMID: 23383834 DOI: 10.1103/physrevlett.110.017203] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Indexed: 06/01/2023]
Abstract
The spin glass state in the spinel ZnCr(2(1-x))Ga(2x)O(4) is studied with magnetization and specific heat for x < 0.05. The freezing temperature is independent of disorder, despite a two-level-like density of states that varies linearly with x. This relationship implies the energy scale for freezing is independent of disorder, in contrast to mean field theories of spin glass. We suggest that the degrees of freedom are shielded spin vacancies, quasispins, which interact via an emergent long-range force mediated by the frustrated spin background.
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Affiliation(s)
- A D LaForge
- University of California, Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA
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Ramirez AP, Cava RJ, Espinosa GP, Remeika JP, Batlogg B, Zahurak S, Rietman EA. Specific Heat Linear Term in YBa2Cu3O7−x and a Survey of Related Compounds. ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-99-459] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ABSTRACTWe have measured the specific heat, C, in the temperature range 0.3 to 20K and in magnetic fields up to 12 Tesla of several compounds related to the high-Tc superconductors. The linear term in C for YBa2Cu3O7−x is only weakly dependent on oxygen concentration in the range 0 ≤ × ≤ 0.7. The linear term in C changes by less than 10% at 10 Tesla for La1.98Sr.02CuO4, whereas for YBa2Cu3O7−x it is obscured by additional field-dependent structure. Magnetic ordering anomalies are observed in YBa2Cu2O5 at 10.6 K and in BaCuO2+6 at 9.3 K.
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Abstract
ABSTRACTThe effect of changes of oxygen stoichiometry on the properties of Ba2YC3O7-σ is discussed. Crystallographic, susceptability, resistivity, and specific heat data from 1 set of samples prepared by Zr gettered annealing are described and discussed.
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Hohl H, Ramirez AP, Kaefer W, Fess K, Thurner C, Kloc C, Bucher E. A New Class of Materials with Promising Thermoelectric Properties: MNiSn (M = Ti, Zr, Hf). ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-478-109] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractTiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about –200 μV/K and resistivities of a few mΩcm, power factors S2/ρ as high as 38 μW/K2 cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zrl−xHfxNiSn, Zrl−xTixNiSn, and Hfl−xTixNiSn were formed. The figure of merit of Zr0.5Hf0.5NiSn at 700 K (ZT = 0.41) exceeds the end members ZrNiSn (ZT = 0.26) and HfNiSn (ZT = 0.22).
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Thorsmølle VK, Averitt RD, Demsar J, Smith DL, Tretiak S, Martin RL, Chi X, Crone BK, Ramirez AP, Taylor AJ. Morphology effectively controls singlet-triplet exciton relaxation and charge transport in organic semiconductors. Phys Rev Lett 2009; 102:017401. [PMID: 19257238 DOI: 10.1103/physrevlett.102.017401] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Indexed: 05/24/2023]
Abstract
We present a comparative study of ultrafast photoconversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photoinduced absorption in Tc and Pc crystals is activated and temperature-independent, respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as C60-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.
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Affiliation(s)
- V K Thorsmølle
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Mizoguchi H, Zakharov LN, Ramirez AP, Marshall WJ, Sleight AW, Subramanian MA. New A2/3-xRh2O4 compounds with the CaFe2O4 structure where A is a rare earth or Bi. Inorg Chem 2009; 48:204-8. [PMID: 19049419 DOI: 10.1021/ic801603t] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
New compounds of the type R(2/3-x)Rh(2)O(4) with the CaFe(2)O(4) structure have been prepared, where R is a rare earth. For crystals grown in a Bi/V/O flux, the rare earth was partially replaced by Bi. No evidence of ordering of the A cation vacancies is found, but the A cations are displaced from the ideal A cation site by about 0.24 A. Electrical conductivity measurements on crystals suggest that the materials are degenerate semiconductors with Seebeck measurements showing p-type behavior. This is consistent with our observation that x in R(2/3-x)Rh(2)O(4) ranges up to about 0.09. The compounds were also characterized by magnetic susceptibility and diffuse reflectance measurements.
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Affiliation(s)
- Hiroshi Mizoguchi
- Department of Chemistry and Oregon University Materials Institute, Oregon State University, Corvallis, Oregon 97331-4003, USA
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Manyala N, DiTusa JF, Aeppli G, Ramirez AP. Doping a semiconductor to create an unconventional metal. Nature 2008; 454:976-80. [DOI: 10.1038/nature07137] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2008] [Accepted: 05/23/2008] [Indexed: 11/09/2022]
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Schlesinger Z, Rosen JA, Hancock JN, Ramirez AP. Soft manifold dynamics behind negative thermal expansion. Phys Rev Lett 2008; 101:015501. [PMID: 18764122 DOI: 10.1103/physrevlett.101.015501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2006] [Indexed: 05/26/2023]
Abstract
Minimal models are developed to examine the origin of large negative thermal expansion in underconstrained systems. The dynamics of these models reveals how underconstraint can organize a thermodynamically extensive manifold of low-energy modes which not only drives negative thermal expansion but extends across the Brillioun zone. Mixing of twist and translation in the eigenvectors of these modes, for which in ZrW2O8 there is evidence from infrared and neutron scattering measurements, emerges naturally in our model as a signature of the dynamics of underconstraint.
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Affiliation(s)
- Z Schlesinger
- Physics Department, University of California Santa Cruz, Santa Cruz, California 95064, USA
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17
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Kimura T, Sekio Y, Nakamura H, Siegrist T, Ramirez AP. Cupric oxide as an induced-multiferroic with high-TC. Nat Mater 2008; 7:291-294. [PMID: 18297078 DOI: 10.1038/nmat2125] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Accepted: 01/18/2008] [Indexed: 05/25/2023]
Abstract
Materials that combine coupled electric and magnetic dipole order are termed 'magnetoelectric multiferroics'. In the past few years, a new class of such materials, 'induced-multiferroics', has been discovered, wherein non-collinear spiral magnetic order breaks inversion symmetry, thus inducing ferroelectricity. Spiral magnetic order often arises from the existence of competing magnetic interactions that reduce the ordering temperature of a more conventional collinear phase. Hence, spiral-phase-induced ferroelectricity tends to exist only at temperatures lower than approximately 40 K. Here, we propose that copper(II) oxides (containing Cu2+ ions) having large magnetic superexchange interactions can be good candidates for induced-multiferroics with high Curie temperature (T(C)). In fact, we demonstrate ferroelectricity with T(C)=230 K in cupric oxide, CuO (tenorite), which is known as a starting material for the synthesis of high-T(c) (critical temperature) superconductors. Our result provides an important contribution to the search for high-temperature magnetoelectric multiferroics.
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Affiliation(s)
- T Kimura
- Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
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Kenzelmann M, Lawes G, Harris AB, Gasparovic G, Broholm C, Ramirez AP, Jorge GA, Jaime M, Park S, Huang Q, Shapiro AY, Demianets LA. Direct transition from a disordered to a multiferroic phase on a triangular lattice. Phys Rev Lett 2007; 98:267205. [PMID: 17678126 DOI: 10.1103/physrevlett.98.267205] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Indexed: 05/16/2023]
Abstract
We report the first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)(2). Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment.
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Affiliation(s)
- M Kenzelmann
- Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich, Switzerland
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Kimura T, Lawes G, Ramirez AP. Magnetic control of electric polarization in magnetic oxides with non-collinear magnetic structures. Acta Crystallogr A 2005. [DOI: 10.1107/s0108767305094948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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20
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Lawes G, Harris AB, Kimura T, Rogado N, Cava RJ, Aharony A, Entin-Wohlman O, Yildirim T, Kenzelmann M, Broholm C, Ramirez AP. Magnetically driven ferroelectric order in Ni3V2O8. Phys Rev Lett 2005; 95:087205. [PMID: 16196898 DOI: 10.1103/physrevlett.95.087205] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Indexed: 05/04/2023]
Abstract
We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.
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Affiliation(s)
- G Lawes
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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21
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Kimura T, Lawes G, Ramirez AP. Electric polarization rotation in a hexaferrite with long-wavelength magnetic structures. Phys Rev Lett 2005; 94:137201. [PMID: 15904022 DOI: 10.1103/physrevlett.94.137201] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2004] [Indexed: 05/02/2023]
Abstract
We report on the control of electric polarization (P) by using magnetic fields (B) in a hexaferrite having magnetic order above room temperature (RT). The material investigated is hexagonal Ba0.5Sr1.5Zn2Fe12O22, which is a nonferroelectric helimagnetic insulator in the zero-field ground state. By applying B, the system undergoes successive metamagnetic transitions, and shows concomitant ferroelectric order in some of the B-induced phases with long-wavelength magnetic structures. The magnetoelectrically induced P can be rotated 360 degrees by external B. This opens up the potential for not only RT magnetoelectric devices but also devices based on the magnetically controlled electro-optical response.
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Affiliation(s)
- T Kimura
- Los Alamos National Laboratory, K764, Los Alamos, New Mexico 87545, USA
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22
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McDonald RD, Harrison N, Singleton J, Bangura A, Goddard PA, Ramirez AP, Chi X. Landau quantization effects in the charge-density-wave system (Per)2M(mnt)2 (where M = Au and Pt). Phys Rev Lett 2005; 94:106404. [PMID: 15783500 DOI: 10.1103/physrevlett.94.106404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2004] [Indexed: 05/24/2023]
Abstract
A finite transfer integral t(a) orthogonal to the conducting chains of a highly one-dimensional metal gives rise to empty and filled bands that simulate an indirect-gap semiconductor upon formation of a charge-density wave (CDW). In contrast to semiconductors such as Ge and Si with band gaps approximately 1 eV, the CDW system possesses an indirect gap with a greatly reduced energy scale, enabling moderate laboratory magnetic fields to have a major effect. The consequent variation of the thermodynamic gap with magnetic field due to Zeeman splitting and Landau quantization enables the electronic band structure parameters (transfer integrals, Fermi velocity) to be determined accurately. These parameters reveal the orbital quantization limit to be reached at approximately 20 T in (Per)2M(mnt)(2) salts, making them highly unlikely candidates for a recently proposed cascade of field-induced CDW states.
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Affiliation(s)
- R D McDonald
- National High Magnetic Field Laboratory, LANL, MS-E536, Los Alamos, New Mexico 87545, USA
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23
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Gao XPA, Boebinger GS, Mills AP, Ramirez AP, Pfeiffer LN, West KW. Strongly enhanced hole-phonon coupling in the metallic state of the dilute two-dimensional hole gas. Phys Rev Lett 2005; 94:086402. [PMID: 15783911 DOI: 10.1103/physrevlett.94.086402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/03/2004] [Indexed: 05/24/2023]
Abstract
We have studied the temperature dependent phonon emission rate P(T) of a strongly interacting (r(s) > or =22) dilute 2D GaAs hole system using a standard carrier heating technique. In the still poorly understood metallic state, we observe that P(T) changes from P(T) approximately T5 to P(T) approximately T7 above 100 mK, indicating a crossover from screened piezoelectric (PZ) coupling to screened deformation potential (DP) coupling for hole-phonon scattering. Quantitative comparison with theory shows that the long range PZ coupling between holes and phonons has the expected magnitude; however, in the metallic state, the short range DP coupling between holes and phonons is almost 20 times stronger than expected from theory. The density dependence of P(T) shows that it is easier to cool low-density 2D holes in GaAs than higher density 2D hole systems.
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Affiliation(s)
- X P A Gao
- Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
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Gao XPA, Boebinger GS, Mills AP, Ramirez AP, Pfeiffer LN, West KW. Temperature and magnetic-field-enhanced hall slope of a dilute 2D hole system in the ballistic regime. Phys Rev Lett 2004; 93:256402. [PMID: 15697919 DOI: 10.1103/physrevlett.93.256402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2004] [Indexed: 05/24/2023]
Abstract
We report the temperature (T) and perpendicular magnetic-field (B) dependence of the Hall resistivity rho(xy)(B) of dilute metallic 2D holes in GaAs over a broad range of temperature (0.02-1.25 K). The low B Hall coefficient, R(H), is found to be enhanced when T decreases. Strong magnetic fields further enhance the slope of rho(xy)(B) at all temperatures studied. Coulomb interaction corrections of a Fermi liquid (FL) in the ballistic regime can not explain the enhancement of rho(xy) which occurs in the same regime as the anomalous metallic longitudinal conductivity. In particular, although the metallic conductivity in 2D systems has been attributed to electron interactions in a FL, these same interactions should reduce, not enhance, the slope of rho(xy)(B) as T decreases and/or B increases.
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Affiliation(s)
- X P A Gao
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
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25
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Lawes G, Kenzelmann M, Rogado N, Kim KH, Jorge GA, Cava RJ, Aharony A, Entin-Wohlman O, Harris AB, Yildirim T, Huang QZ, Park S, Broholm C, Ramirez AP. Competing magnetic phases on a kagomé staircase. Phys Rev Lett 2004; 93:247201. [PMID: 15697855 DOI: 10.1103/physrevlett.93.247201] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2004] [Indexed: 05/24/2023]
Abstract
We present thermodynamic and neutron data on Ni3V2O8, a spin-1 system on a kagomé staircase. The extreme degeneracy of the kagomé antiferromagnet is lifted to produce two incommensurate phases at finite T--one amplitude modulated, the other helical--plus a commensurate canted antiferromagnet for T-->0. The H-T phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. Ni3V2O8 thus provides an elegant example of order from subleading interactions in a highly frustrated system.
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Affiliation(s)
- G Lawes
- Los Alamos National Laboratory, Los Alamos, NM 87544, USA
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26
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Lang DV, Chi X, Siegrist T, Sergent AM, Ramirez AP. Amorphouslike density of gap states in single-crystal pentacene. Phys Rev Lett 2004; 93:086802. [PMID: 15447213 DOI: 10.1103/physrevlett.93.086802] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2003] [Indexed: 05/24/2023]
Abstract
We show that optical and electrical measurements on pentacene single crystals can be used to extract the density of states in the highest occupied molecular orbital-lowest unoccupied molecular orbital band gap. It is found that these highly purified crystals possess band tails broader than those typically observed in inorganic amorphous solids. Results on field-effect transistors fabricated from similar crystals imply that the gap state density is much larger within 5-10 nm of the gate dielectric. Thus, organic thin-film transistors for such applications as flexible displays might be significantly improved by reducing these defects.
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Affiliation(s)
- D V Lang
- Los Alamos National Laboratory, Los Alamos, NM 87545, USA
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27
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Lang DV, Chi X, Siegrist T, Sergent AM, Ramirez AP. Bias-dependent generation and quenching of defects in pentacene. Phys Rev Lett 2004; 93:076601. [PMID: 15324261 DOI: 10.1103/physrevlett.93.076601] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2003] [Indexed: 05/24/2023]
Abstract
We describe a defect generation phenomenon that is new to organic semiconductors. A defect in pentacene single crystals can be created by bias-stress and persists at room temperature for an hour in the dark but only seconds with 420 nm illumination. The defect gives rise to a hole trap at Ev+0.38 eV and causes metastable transport effects at room temperature. Creation and decay rates of the hole trap have a 0.67 eV activation energy with a small (10(8) s(-1)) prefactor, suggesting that atomic motion plays a key role in the generation and quenching process.
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Affiliation(s)
- D V Lang
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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28
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Drymiotis FR, Ledbetter H, Betts JB, Kimura T, Lashley JC, Migliori A, Ramirez AP, Kowach GR, Van Duijn J. Monocrystal elastic constants of the negative-thermal-expansion compound zirconium tungstate (ZrW2O8). Phys Rev Lett 2004; 93:025502. [PMID: 15323925 DOI: 10.1103/physrevlett.93.025502] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2004] [Indexed: 05/24/2023]
Abstract
We measured zirconium tungstate's elastic constants C(ij). This compound shows relatively soft, nearly isotropic elastic constants with normal Poisson ratios and no approach to Born instability. ZrW2O8 shows normal ambient-temperature elastic constants C(ij), but remarkable dC(ij)/dT that show dominant low-frequency acoustic-vibration modes. From the bulk modulus, we estimated the total ambient-temperature thermodynamic Grüneisen parameter as gamma = -1.2. The dB/dT slope gives a Grüneisen parameter gamma = -7. The 300-0 K bulk-modulus increase (40%) seems unprecedented and breaks Birch's law of corresponding states.
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Affiliation(s)
- F R Drymiotis
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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29
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Goto T, Kimura T, Lawes G, Ramirez AP, Tokura Y. Ferroelectricity and giant magnetocapacitance in perovskite rare-earth manganites. Phys Rev Lett 2004; 92:257201. [PMID: 15245056 DOI: 10.1103/physrevlett.92.257201] [Citation(s) in RCA: 185] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2003] [Indexed: 05/24/2023]
Abstract
The relationships among magnetism, lattice modulation, and dielectric properties have been investigated for RMnO3 (R=Eu, Gd, Tb, and Dy). These compounds show a transition to an incommensurate lattice structure below their Néel temperature, and subsequently undergo an incommensurate-commensurate (IC-C) phase transition. For TbMnO3 and DyMnO3 it was found that the IC-C transition is accompanied by a ferroelectric transition, associated with a lattice modulation in the C phase. DyMnO3 shows a gigantic magnetocapacitance with a change of dielectric constant up to Deltaepsilon/epsilon approximately 500%.
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Affiliation(s)
- T Goto
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
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30
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Lawes G, Ramirez AP, Varma CM, Subramanian MA. Magnetodielectric effects from spin fluctuations in isostructural ferromagnetic and antiferromagnetic systems. Phys Rev Lett 2003; 91:257208. [PMID: 14754152 DOI: 10.1103/physrevlett.91.257208] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2003] [Indexed: 05/24/2023]
Abstract
We report on the effects of spin fluctuations, magnetic ordering, and external magnetic field on the dielectric constant of the ferromagnet SeCuO3, and the antiferromagnet TeCuO3. A model based on the coupling between uniform polarization and the q-dependent spin-spin correlation function is presented to explain the different behaviors for these isostructural compounds. The large magnetocapacitance near the transition temperature in the ferromagnet SeCuO3 suggests routes to enhancing the magnetodielectric response for practical applications.
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Affiliation(s)
- G Lawes
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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31
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Affiliation(s)
- A P Ramirez
- Materials Integration Science Laboratory and the Institute for Complex Adaptive Matter, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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Cao D, Bridges F, Kowach GR, Ramirez AP. Frustrated soft modes and negative thermal expansion in ZrW2O8. Phys Rev Lett 2002; 89:215902. [PMID: 12443433 DOI: 10.1103/physrevlett.89.215902] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2002] [Indexed: 05/24/2023]
Abstract
Negative thermal expansion (NTE) in cubic ZrW2O8 has generated much interest due to its large, isotropic, and temperature independent behavior. Here, x-ray absorption fine structure data are presented for various atom pairs, providing evidence that the low-energy modes causing NTE correspond to the correlated vibrations of a WO4 tetrahedron and its three nearest ZrO6 octahedra. This involves translations of the WO4 as a rigid unit along each of the four <111> axes. The interconnectivity of these modes prevents an anisotropic soft mode from developing, a new geometrical phenomenon that we call the "frustrated soft mode."
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Affiliation(s)
- D Cao
- Physics Department, University of California, Santa Cruz, California 95064, USA
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33
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Ramirez AP, Shastry BS, Hayashi A, Krajewski JJ, Huse DA, Cava RJ. Multiple field-induced phase transitions in the geometrically frustrated dipolar magnet: Gd(2) Ti(2)O(7). Phys Rev Lett 2002; 89:067202. [PMID: 12190608 DOI: 10.1103/physrevlett.89.067202] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2001] [Indexed: 05/23/2023]
Abstract
Field-driven phase transitions generally arise from competition between Zeeman energy and exchange or crystal-field anisotropy. Here we present the phase diagram of a frustrated pyrochlore magnet Gd(2)Ti(2)O(7), where crystal-field splitting is small compared to the dipolar energy. We find good agreement between zero-temperature critical fields and those obtained from a mean-field model. Here, dipolar interactions couple real space and spin space, so the transitions in Gd(2)Ti(2)O(7) arise from field-induced "cooperative anisotropy," reflecting the broken spatial symmetries of the pyrochlore lattice.
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Affiliation(s)
- A P Ramirez
- Los Alamos National Laboratory, K764, New Mexico 87545, USA
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Abstract
Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.
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Affiliation(s)
- C C Homes
- Department of Physics, Building 510B, Brookhaven National Laboratory, Upton, NY 11973-5000, USA.
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Abstract
Understanding the complexities of electronic and magnetic ground states in solids is one of the main goals of solid-state physics. Transition-metal oxides have proved to be particularly fruitful in this regard, especially for those materials with the perovskite structure, where the special characteristics of transition-metal-oxygen orbital hybridization determine their properties. Ruthenates have recently emerged as an important family of perovskites because of the unexpected evolution from high-temperature ferromagnetism in SrRuO3 to low-temperature superconductivity in Sr2RuO4 (refs 1, 2). Here we show that a ruthenate in a different structural family, La4Ru6O19, displays a number of highly unusual properties, most notably non-Fermi-liquid behaviour. The properties of La4Ru6O19 have no analogy among the thousands of previously characterized transition-metal oxides. Instead, they resemble those of CeCu6-xAux-a widely studied f-electron-based heavy fermion intermetallic compound that is often considered as providing the best example of non-Fermi-liquid behaviour. In the ruthenate, non-Fermi-liquid behaviour appears to arise from just the right balance between the interactions of localized electronic states derived from Ru-Ru bonding and delocalized states derived from Ru-O hybridization.
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Affiliation(s)
- P Khalifah
- Department of Chemistry and Princeton Materials Institute, Princeton University, Princeton, New Jersey 08540, USA
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He T, Huang Q, Ramirez AP, Wang Y, Regan KA, Rogado N, Hayward MA, Haas MK, Slusky JS, Inumara K, Zandbergen HW, Ong NP, Cava RJ. Superconductivity in the non-oxide perovskite MgCNi3. Nature 2001; 411:54-6. [PMID: 11333973 DOI: 10.1038/35075014] [Citation(s) in RCA: 530] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The interplay of magnetic interactions, the dimensionality of the crystal structure and electronic correlations in producing superconductivity is one of the dominant themes in the study of the electronic properties of complex materials. Although magnetic interactions and two-dimensional structures were long thought to be detrimental to the formation of a superconducting state, they are actually common features of both the high transition-temperature (Tc) copper oxides and low-Tc material Sr2RuO4, where they appear to be essential contributors to the exotic electronic states of these materials. Here we report that the perovskite-structured compound MgCNi3 is superconducting with a critical temperature of 8 K. This material is the three-dimensional analogue of the LnNi2B2C family of superconductors, which have critical temperatures up to 16 K (ref. 2). The itinerant electrons in both families of materials arise from the partial filling of the nickel d-states, which generally leads to ferromagnetism as is the case in metallic Ni. The high relative proportion of Ni in MgCNi3 suggests that magnetic interactions are important, and the lower Tc of this three-dimensional compound-when compared to the LnNi2B2C family-contrasts with conventional ideas regarding the origins of superconductivity.
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Affiliation(s)
- T He
- Department of Chemistry and Princeton Materials Institute, Princeton, New Jersey, USA
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Hagemann IS, Huang Q, Gao XP, Ramirez AP, Cava RJ. Geometric magnetic frustration in Ba(2)Sn(2)Ga(3)ZnCr(7)O(22): a two-dimensional spinel based Kagomé lattice. Phys Rev Lett 2001; 86:894-897. [PMID: 11177967 DOI: 10.1103/physrevlett.86.894] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2000] [Indexed: 05/23/2023]
Abstract
The properties of a two-dimensional geometrically frustrated magnetic material based on the Kagomé net, Ba(2)Sn(2)ZnGa(3)Cr(7)O(22), are reported. The Kagomé net is fully filled with magnetic ions. A Curie-Weiss theta theta(W) = -312 K is found with a spin glass transition at approximately 1.5 K, indicating strong geometrical magnetic frustration. This compound is the most two dimensional of a structural series with the geometrically frustrated materials ZnCr(2)O(4) and SrCr(8)Ga(4)O(19). The comparison of their properties tests the influence of different degrees of coupling between Kagomé layers on magnetic frustration within a single chemical and structural family.
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Affiliation(s)
- I S Hagemann
- Department of Chemistry and Princeton Materials Institute, Princeton University, New Jersey 08544, USA
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38
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Ramirez AP, Hessen B, Winklemann M. Entropy balance and evidence for local spin singlets in a Kagome-like magnet. Phys Rev Lett 2000; 84:2957-2960. [PMID: 11018985 DOI: 10.1103/physrevlett.84.2957] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/1999] [Indexed: 05/23/2023]
Abstract
We have measured the specific heat C(T) of the S = 3 / 2 Kagome-lattice-containing compound SrCr (9p)Ga (12-9p)O (19). We find little field dependence of the low-temperature C(T), consistent with a low-energy spectrum dominated by many-body singlet excitations. At high temperatures, we recover only approximately 50% of the total R ln4 entropy.
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Affiliation(s)
- AP Ramirez
- Bell Labs, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
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Gammel PL, Barber B, Lopez D, Ramirez AP, Bishop DJ, Bud'ko SL, Canfield PC. Enhanced critical currents of superconducting ErNi2B2C in the ferromagnetically ordered state. Phys Rev Lett 2000; 84:2497-2500. [PMID: 11018919 DOI: 10.1103/physrevlett.84.2497] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/1999] [Indexed: 05/23/2023]
Abstract
We report on transport and magnetization studies of the critical current in single crystal ErNi2B2C for applied fields below 4 kG. Below T approximately 2.5 K superconductivity coexists with weak ferromagnetism. We find that the critical currents are strongly enhanced for all field orientations in this ferromagnetic regime, corresponding to a threefold increase of the pinning force of the flux line lattice. We speculate that this increase is due to strong pair breaking by the ferromagnetism.
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Affiliation(s)
- PL Gammel
- Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA
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40
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Eskildsen MR, Harada K, Gammel PL, Abrahamsen AB, Andersen NH, Ernst G, Ramirez AP, Bishop DJ, Mortensen K, Naugle DG, Rathnayaka KDD, Canfield PC. Intertwined symmetry of the magnetic modulation and the flux-line lattice in the superconducting state of TmNi2B2C. Nature 1998. [DOI: 10.1038/30447] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- A. P. Ramirez
- A. P. Ramirez, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974–0636, USA
- M. A. Subramanian, DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880–0328, USA
| | - M. A. Subramanian
- A. P. Ramirez, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974–0636, USA
- M. A. Subramanian, DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880–0328, USA
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Subramanian MA, Greedan JE, Raju NP, Ramirez AP, Sleight AW. Structure, Magnetism and Colossal Magnetoresistance Behavior in A2Mn2O7 Pyrochlores (A = Dy-Lu, Y, Sc, In or Tl). ACTA ACUST UNITED AC 1997. [DOI: 10.1051/jp4:19971258] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Schiffer P, Ramirez AP, Franklin KN, Cheong SW. Interaction-Induced Spin Coplanarity in a Kagomé Magnet: SrCr9pGa 12-9pO19. Phys Rev Lett 1996; 77:2085-2088. [PMID: 10061853 DOI: 10.1103/physrevlett.77.2085] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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D'Anna G, Gammel PL, Ramirez AP, Yaron U, Oglesby CS, Bucher E, Bishop DJ. Evidence of surface superconductivity in 2H-NbSe2 single crystals. Phys Rev B Condens Matter 1996; 54:6583-6586. [PMID: 9986676 DOI: 10.1103/physrevb.54.6583] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Radaelli PG, Cox DE, Marezio M, Cheong SW, Schiffer PE, Ramirez AP, Argyriou DN, Jorgensen JD. Structural 'tuning' of magnetism in A1−xA′ xMnO 3( A= La, Pr; A′ = Ca, Sr, Ba). Acta Crystallogr A 1996. [DOI: 10.1107/s0108767396084103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
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Subramanian MA, Toby BH, Ramirez AP, Marshall WJ, Sleight AW, Kwei GH. Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7. Science 1996; 273:81-4. [PMID: 8688054 DOI: 10.1126/science.273.5271.81] [Citation(s) in RCA: 284] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.94 to 2.00 angstroms) observed in phases based on LaMnO3 perovskites that exhibit CMR. Both results in Tl2Mn2O7 indicate oxidation states very close to Tl23+Mn24+O7. Thus, Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials. An alternate mechanism for CMR in Tl2Mn2O7 based on magnetic ordering driven by superexchange and strong spin-fluctuation scattering above the Curie temperature is proposed here.
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Affiliation(s)
- MA Subramanian
- M. A. Subramanian and W. J. Marshall, Dupont Central Research and Development, Experimental Station, Wilmington, DE 19880-0328, USA. B. H. Toby, Reactor Radiation Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA. A. P. Ramirez, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974, USA. A. W. Sleight, Department of Chemistry, Oregon State University, Corvallis, OR 97331, USA. G. H. Kwei, Chemistry and Materials Sciences Department, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
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Ramirez AP, Schiffer P, Cheong SW, Chen CH, Bao W, Palstra TT, Gammel PL, Bishop DJ, Zegarski B. Thermodynamic and electron diffraction signatures of charge and spin ordering in La1- xCaxMnO3. Phys Rev Lett 1996; 76:3188-3191. [PMID: 10060897 DOI: 10.1103/physrevlett.76.3188] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Ramirez AP, Gammel PL, Cheong SW, Bishop DJ, Chandra P. Charge modulation in La1.67Sr0.33NiO4: A bulk thermodynamic study. Phys Rev Lett 1996; 76:447-450. [PMID: 10061459 DOI: 10.1103/physrevlett.76.447] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Radaelli PG, Cox DE, Marezio M, Cheong SW, Schiffer PE, Ramirez AP. Simultaneous structural, magnetic, and electronic transitions in La1-xCaxMnO3 with x=0.25 and 0.50. Phys Rev Lett 1995; 75:4488-4491. [PMID: 10059921 DOI: 10.1103/physrevlett.75.4488] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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