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High field magnetotransport and specific heat in YbAgCu{sub 4}

Description: The electrical resistivity ({rho}) and magnetoresistance of polycrystalline YbAgCu{sub 4} have been measured at temperatures between 25 mK and 300 K, and at magnetic fields (B) to 18 T. The magnetoresistance ({rho}(B){minus}{rho}(0))/{rho}(0) is positive at all temperatures below 200 K and reaches its maximum of 60% at 18 T and 25 mK. The field- and temperature-dependent resistivity does not scale in a simple way. The opposite magnetoresistance behaviors at ambient and high pressure can be expl… more
Date: July 1, 1994
Creator: Lacerda, A.; Graf, T.; Hundley, M. F.; Thompson, J. D.; Gajewski, D.; Canfield, P. C. et al.
Partner: UNT Libraries Government Documents Department
open access

Science and technology of reduced-dimensional magnetic materials

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work involved the synthesis of single crystal and thin film samples of magnetoresistive manganites (LaMnO{sub 3} doped with Ca and Sr) and the characterization of their electronic transport properties to understand the underlying physical mechanisms responsible for the colossal magnetoresistance (CMR) of these materials. The experimental program wa… more
Date: December 31, 1998
Creator: Heffner, R. H.; Bishop, A. R.; Hundley, M. F.; Jia, Q.; Neumeier, J. J.; Trugman, S. A. et al.
Partner: UNT Libraries Government Documents Department
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Cerium heavy-fermion compounds near their T = 0 magnetic-non-magnetic boundary

Description: Measurements of the temperature-dependent specific heat and thermal expansion coefficient near a T = 0 magnetic-non-magnetic boundary, accessed in CeRh{sub 2}Si{sub 2} by application of pressure and in CeRh{sub 2{minus}x}Ru{sub x}Si{sub 2} at ambient pressure by chemical substitution, emphasize the role of disorder in producing non-Fermi-liquid behavior. Interestingly, superconductivity also develops near this boundary in some crystallographically-ordered Ce-based heavy-fermion compounds.
Date: December 1, 1997
Creator: Thompson, J. D.; Hundley, M. F.; Movshovich, R.; Sarrao, J. L.; Graf, T.; Uwatoko, Y. et al.
Partner: UNT Libraries Government Documents Department
open access

Characterization of advanced electronic materials

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Our goal has been to extend the Laboratory`s competency in nuclear and advanced materials by characterizing (measuring and interpreting) physical properties of advanced electronic materials and in this process to bridge the gap between materials synthesis and theoretical understanding. Attention has focused on discovering new physics by understandin… more
Date: August 1, 1997
Creator: Arko, A. J.; Heffner, R. H. & Hundley, M. F.
Partner: UNT Libraries Government Documents Department
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Growth and magnetic structure of La{sub 0.67}Sr{sub 0.33}MnO{sub 3} films

Description: Growth of LaMnO{sub 3} films that exhibit colossal magnetoresistance (CMR) has concentrated heavily on Ca doped materials. However, since the 33% Sr doped films are ferromagnetic at room temperature, they are ideal candidates for dual growth-magnetic structure studies using scanned probe techniques. In this study, interest was focused on the relations between growth/processing parameters, film morphology, and electronic/magnetic properties. In addition, films were grown on both LaAlO{sub 3} (LA… more
Date: August 1, 1997
Creator: Brown, G. W.; Jia, Q. X.; Peterson, E. J.; Hristova, D. K.; Hundley, M. F.; Thompson, J. D. et al.
Partner: UNT Libraries Government Documents Department
open access

Response of CeRh{sub 2}Si{sub 2} to pressure

Description: Under atmospheric pressure, CeRh{sub 2}Si{sub 2} orders antiferromagnetically at T{sub N} = 35 K, with magnetic entropy S = R{ell}n2 associated with the ordered groundstate. Application of modest pressure ({approx}9 kbar) to CeRh{sub 2}Si{sub 2} suppresses T{sub N} to near zero Kelvin, increases its Sommerfeld coefficient of specific heat by nearly a factor of 3.5 and induces some form of superconductivity below 400 mK that is depressed by a magnetic field at a rate of {minus}80 mK/kG.
Date: September 1, 1995
Creator: Movshovich, R.; Hundley, M. F.; Thompson, J. D.; Smith, J. L.; Graf, T.; Mandrus, D. et al.
Partner: UNT Libraries Government Documents Department
open access

Transport and magnetism correlations in thin-film ferromagnetic oxides

Description: In order to determine the {Tc}-dependence of the colossal magnetoresistance (MR) exhibited by the ferromagnetic La{sub 0.7}M{sub 0.3}MnO{sub 3+{sigma}} (M = Ba, Ca, Sr) system, the authors examine the magnetic-field and temperature dependent resistivity and magnetization of a series of thin films that were grown via pulsed-laser deposition. The films had magnetic ordering temperatures (T{sub C}) ranging from 150 to 350 K; all samples displayed a large negative MR that is largest near {Tc}. The … more
Date: September 1, 1995
Creator: Hundley, M. F.; Neumeier, J. J.; Heffner, R. H.; Jia, Q. X.; Wu, X. D. & Thompson, J. D.
Partner: UNT Libraries Government Documents Department
open access

Interplay between electronic transport and magnetic order in ferromagnetic magnetic manganite thin films

Description: The transition metal oxides La{sub 1{minus}x}A{sub x}MnO{sub 3} (A = Ba, Ca, or Sr) order ferromagnetically with Curie temperatures ranging from as low as 50 K to well above room temperature. Magnetic order in these compounds results in a concomitant metal-insulator transition. The feature displayed by the manganites that is most important technologically is the extremely large negative magnetoresistance that achieves its largest values near the magnetic ordering temperature. Qualitatively, thi… more
Date: May 1, 1997
Creator: Hundley, M. F.; Neumeier, J. J.; Heffner, R. H.; Jia, Q. X.; Wu, X. D. & Thompson, J. D.
Partner: UNT Libraries Government Documents Department
open access

Observation of large low field magnetoresistance in ramp-edge tunneling junctions based on doped manganite ferromagnetic electrodes and a SrTiO{sub 3} insulator

Description: The authors report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La{sub 0.7}Sr{sub 0.3})MnO{sub 3} ferromagnetic electrodes and a SrTiO{sub 3} insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the … more
Date: July 1, 1998
Creator: Kwon, C.; Jia, Q. X.; Fan, Y.; Hundley, M. F.; Reagor, D. W.; Hawley, M. E. et al.
Partner: UNT Libraries Government Documents Department
open access

Volume-based considerations for the metal-insulator transition of CMR oxides

Description: The sensitivity of {rho} [electrical resistivity] to changes in volume which occur through: (1) applied pressure, (2) variations in temperature, and (3) phase transitions, is evaluated for some selected CMR oxides. It is argued that the changes in volume associated with phase changes are large enough to produce self pressures in the range of 0.18 to 0.45 GPa. The extreme sensitivity of the electrical resistivity to pressure indicates that these self pressures are responsible for large features … more
Date: March 1, 1998
Creator: Neumeier, J. J.; Hundley, M. F.; Cornelius, A. L. & Andres, K.
Partner: UNT Libraries Government Documents Department
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