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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic susceptibility χ(parallel)(H(parallel)b), χ⊥(H⊥b) (2≤T≤700 K) and electrical resistivity ρ(T) (2≤T≤300 K) of single crystal Na2Ru4O9−δ (δ≥0) with various oxygen content were measured. The crystal structure of this compound is monoclinic with single, double, and triple chains along the b axis. The most striking feature of this compound is the drastically large anisotropy reflected in the resistivity which exhibits metallic behavior along chains and semiconducting behavior perpendicular to the chains. The resistivity ratio for these two directions (ρ⊥/ρ(parallel)) is larger than 105. This ratio is exceptionally large, indicating that the anisotropy of the bandwidth is substantial. It is remarkable that, after reduction of oxygen content in the system, the magnetic susceptibility undergoes a drastic change, whereas the electrical resistivity along the conducting chains is altered only slightly. It is argued that the different sensitivity to oxygen content reflected in magnetic and transport properties may be attributed to the complexity of the crystal structure. The striking observations presented here may suggest a one-dimensional system that possesses unique physical properties. © 1996 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4821-4823 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic susceptibility χ(T) (2≤T≤400 K) and electrical resistivity ρ(T) (2≤T≤300 K) of undoped and Na doped SrRuO3 and CaRuO3 single crystals were measured. These two perovskites are orthorhombic with space group Pbnm. While both of the undoped systems exhibit metallic conductivity, SrRuO3 is ferromagnetic with Tc≤160 K, but CaRuO3 is paramagnetic. When a small concentration of Na (≤12%) replaces Sr in the structure, SrRuO3 becomes an insulator with a depressed ferromagnetic response. In contrast, Na doped CaRuO3 (≤5%) remains metallic with the appearance of antiferromagnetism below 70 K. The dramatic changes in magnetic and transport properties resulting from Na replacement of Sr and Ca reflects the very subtle differences driving the magnetism in SrRuO3 and CaRuO3. © 1996 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6748-6750 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of an isolated ferromagnetic bond of coupling constant K embedded in a layered spin-1/2 Heisenberg antiferromagnet with interplane coupling strength J⊥=αJ(parallel) (0≤α≤1.0) have been studied using linear-spin-wave (LSW) theory. In the pure lattice, the sublattice magnetization 〈Szi〉 is 0.304 at α=0 and saturates to 0.422 at α=1.0. The spin correlations 〈SxiSxj〉 decrease with increasing α within the plane and increase along the interplane direction. The introduction of an isolated ferromagnetic bond into the host lattice tends to enhance 〈Szi〉 at lattice sites joining the bond as K approaches zero. Increasing K will drastically suppress 〈SxiSxj〉 across the bond. Whereas, 〈SxiSxj〉 is enhanced between the neighboring sites close to the impurity link resulting in the suppression of 〈Szi〉. This behavior persists for all α values. The LSW theory breaks down at a certain K value. Increasing α, the critical value of K extends to a larger number.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 6989-6991 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the thermal conductivity K(T,B) (6〈T〈250 K, 0〈B〈15 T) of single crystals of SrRuO3, a ferromagnet with Tc=160 K, and isostructural but paramagnetic CaRuO3, as well as the intermediate crystals (Sr, Ca)RuO3 for the purpose of probing charge carrier (Ke), phonon (Kp), and magnon (Km) excitations in these systems. The contributions of electron and phonon scattering processes to the thermal conductivities have been estimated using a Wiedemann–Franz relationship to estimate Ke and thus obtain Kp at higher temperatures. Roughly 50% of the thermal conductivity is estimated to be phononic near room temperature. Amorphous behavior is observed in the doped samples, and no break in the thermal conductivity is seen at the ferromagnetic onset. A comparison of magnetothermal conductivity and magnetoresistivity measurements at lower temperatures in SrRuO3 and CaRuO3 reveals that additional scattering mechanisms have become important. These investigations argue for the importance of phonon and magnon contributions, in addition to electronic contributions, to the magnetic behavior in Sr1−xCaxRuO3. Results will be discussed in relation to recent theoretical work on these systems and measurements on related systems. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4978-4980 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic susceptibility, transport properties (including magnetoresistivity and the Hall effect), and specific heat of perovskite ARuO3 (A=Ca, Sr, and Ba) single crystals were measured. These compounds, particularly CaRuO3 (paramagnetic conductor) and SrRuO3 (ferromagnetic conductor) are believed to have a narrow π* band and their thermodynamic properties depend in an extremely sensitive way on the degree of the band filling and band width. This study reveals that the π* bandwidth of these compounds is largely determined by the ionic radii of the alkaline-earth A cations, i.e., the interaction between A s and O 2p orbitals and the electron correlation becomes progressively stronger in the series BaRuO3, SrRuO3, and CaRuO3. © 1997 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical resistivity ρ(T) and magnetic susceptibility χ(T,H) (1.8≤T≤350 K and 0≤H≤5.5 T) have been measured on single crystals and epitaxial thin films of Y1−xTbxBa2Cu3O7. The Tc is 92 K and irrespective of Tb doping up to x=0.50. For T(approximately-greater-than)Tc, ρ(T) has a linear dependence, i.e., ρ(T)≈A+BT, with the reduced resistivity ρ(T)/ρ(250 K) for x=0.10, 0.25, and 0.50, being independent of Tb doping. The results of magnetic susceptibility along with the computation of effective moment of Tb in the presence of crystal electric fields (CEF) tend to suggest that the Tb is mixed valent. The insensitivity of Tc to the Tb doping and the possibility that Tb may be mixed valent are in sharp contrast to the case of Pr and Ce doping which have been shown to be very deleterious to superconductivity. The magnetic susceptibility χ(T) is extremely anisotropic, and this anisotropy cannot be explained by simple models with CEF effects.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A number of specialized facilities have been developed or are under development throughout the world to support research at high magnetic fields in a broad range of science and technology areas. These facilities provide continuous magnetic fields up to 32–35 T and pulsed fields up to 50–70 T for tens of ms periods with fields beyond 100 T for several μs. During the last several years, new laboratories have been planned and are being developed within the United States and Japan with major expansions of facilities occurring in France, The Netherlands, and other countries. The National High Magnetic Field Laboratory, presently under construction in the United States, will include superconducting magnets (B≤20 T), resistive magnets (B≤25–35 T depending on bore and power), hybrid magnet (B≤45–50 T), and pulsed fields (B≤60–70 T for 100 ms, B≤50–70 T for 10–20 ms and B≤250 T for about 10 μs). These new facilities within the United States and elsewhere will expand the research opportunities at the extremes of parameter space, i.e., magnetic field, ultralow temperatures, and high pressures, for researchers in the life and condensed matter science areas. An overview of the facilities throughout the world will be presented along with a brief discussion of the science opportunities and recent results at the extremes of high magnetic field.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transverse AB-plane magnetoresistivity ρAB (C axis (parallel)H) of (Y1−XPrX)Ba2Cu3O7−δ and YBa2(Cu1−XZnX)3O7−δ thin films and (Y1−XTbX)Ba2Cu3O7−δ thin films and single crystals has been measured as a function of 0.0〈X〈XC, 2 K〈T〈300 K, and 0 T〈H〈20 T. Mean-field upper critical field HC2 and irreversibility field HI phase boundaries have been determined and are discussed in terms of proposed theories. Tb doping of YBa2Cu3O7 reflects an enhanced pinning or "stiffening'' of the vortex system without apparent alteration to TC or the slope of the mean-field normal phase-mixed phase boundary line, dHC2/dT||T=Tc. However, Pr and Zn doping of YBa2Cu3O7 tends to depress both TC and dHC2/dT||T=Tc and shows a "softening'' of the vortex system. This behavior may be understood in terms of the magnitude of the superconducting pair coherence length, which is controlled by doping, and the divergence of the vortex-glass correlation length as it relates to flux line coupling of vortices in the CuO2 planes. These systems are compared with other high TC superconducting systems which possess similar phase boundary properties. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6595-6597 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization, magnetic susceptibility, and low-frequency dielectric constant of La2Cu1−xZnxO4+δ (x=0, and 0.07) single crystals were measured. Results obtained in this work show that Zn doping eliminates spins from CuO planes, thus, reducing the correlation length, ξ2D. However, unlike Sr doping, magnetic dilution due to Zn doping is a very local effect, thus suppresses TN relatively slowly and shows little impact on metamagnetic behavior. Our data marks a difference from some results previously reported which claimed a stronger effect on Zn doping on the magnetic properties. It is interesting that Zn doping shows a large influence on the dielectric properties, and resulting in a significant change in the dielectric constant Kc. Most remarkably, the simultaneous polarization and magnetization ordering, described in this study, suggests a coupling of magnetic ordering and electric polarizability in the oxides.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The concentration dependence of the room-temperature lattice constants and the concentration and temperature dependence of the specific heat C(T) and the magnetic susceptibility have been measured on the tetragonal, nonsuperconducting phase of Y1−xPrxBa2Cu3O6. The effective paramagnetic moment μeff is independent of x and has an average value of 2.7±0.2 μB. For PrBa2Cu3O6, the Néel temperature TN for Pr moment ordering is 10.5 K as compared to TN=17 K for the orthorhombic PrBa2Cu3O7 phase. The TN is depressed rapidly with Y doping in the oxygen-depleted compound and goes to zero at x≈0.4–0.5. At low temperatures and x≤0.5, C(T)/T vs T2 is nonlinear and shows a rapid decrease of C(T)/T indicative of strong magnetic correlations.
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