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  • 1
    Digitale Medien
    Digitale Medien
    Dependence of the specific heat of a La1.85Sr0.15CuO4 superconducting single crystal on the magnetic field direction in the a-b plane (1997)
    Springer
    JETP letters 66 (1997), S. 715-719 
    Details
    ISSN: 1090-6487
    Schlagwort(e): 74.72.Dn ; 74.25.Bt ; 65.40.+g
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The low-temperature specific heat of a La1.85Sr0.15CuO4 superconducting single crystal was investigated in magnetic fields up to 8 T and with four orientations — in the a-b plane (along the (100) and (110) directions) and at angles of 45° and 90° with respect to the a-b plane (along the (103) and (001) directions). Anisotropy was observed in the field dependence of the specific heat in the a-b plane. The specific heat was found to be minimum with the field oriented in the direction of the a axis and maximum with the field oriented in a direction making an angle of 45° with the a axis. This can be explained by the anisotropy of the energy gap, whose minimum lies along the (110) direction. For all orientations of the magnetic field the specific heat of the mixed state at low temperatures is a nonlinear function of the magnetic field strength.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.567586
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  • 2
    Digitale Medien
    Digitale Medien
    Anomalous behavior of the specific heat and upper critical magnetic field in the superconducting single crystal La1.85Sr0.15CuO4 (1997)
    Springer
    Journal of experimental and theoretical physics 85 (1997), S. 755-759 
    Details
    ISSN: 1090-6509
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The specific heat and resistive upper critical magnetic field of the single crystal La1.85Sr0.15CuO4 are investigated in the temperature range 2–50 K in magnetic fields up to 8 T for two directions of the magnetic field, parallel and normal to the ab crystalline plane. For both orientations a nonlinear (close to square root) magnetic field dependence of the mixed-state specific heat and a positive curvature of the temperature dependence of the upper critical magnetic field are observed. Neither of these anomalies is described by standard theories of superconductivity. Within the framework of the thermodynamic relations it is shown that in a type-II superconductor a relationship exists between the temperature dependence of the critical magnetic field and the field dependence of the specific heat. The anomalies observed in these phenomena are interrelated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.558363
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  • 3
    Digitale Medien
    Digitale Medien
    Heat capacity of La1−x SrxMnO3 single crystals in different magnetic states (2000)
    Springer
    Physics of the solid state 42 (2000), S. 114-119 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The heat capacity of three single-crystal samples of La1−x SrxMnO3 (x=0, 0.2, and 0.3) is measured in the temperature range 4–400 K. It is found that the heat capacity undergoes abrupt changes due to the transitions from the antiferromagnetic phase to the paramagnetic phase (x=0) and from the ferromagnetic phase to the paramagnetic phase (x=0.2 and 0.3). The phonon contribution to the heat capacity and the Debye characteristic temperatures for the La0.7Sr0.3MnO3 sample are determined over a wide range of temperatures. The electronic density of states at the Fermi level is evaluated. It is demonstrated that an increase in the strontium concentration x brings about an increase in the electronic density of states at the Fermi level. The contributions of spin waves to the heat capacity and the entropy are estimated under the assumption that the phonon spectrum remains unchanged upon doping with Sr.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1131177
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  • 4
    Digitale Medien
    Digitale Medien
    Specific heat of the electronic superconductor Pr1.85Ce0.15CuO4 (1999)
    Springer
    Physics of the solid state 41 (1999), S. 1050-1054 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We have investigated the specific heat of the ceramic Pr1.85Ce0.15CuO4 in the temperature range 2–800K in magnetic fields up to 8 T. We have determined the magnitude of the specific-heat discontinuity at the superconducting transition ΔC/T c and estimate the coefficient of the electronic specific heat. In the temperature interval 5–800K we have separated out the phonon contribution to the specific heat, determined the temperature dependence of the characteristic Debye temperature Θ, and calculated the mean frequencies (moments) of the phonon spectrum. We compare the parameter values obtained in this way with data for the compound La1.85Sr0.15CuO4 having similar crystal structure, but hole conductivity. The magnitude of the specific-heat discontinuity and consequently the effective electron mass in the “electronic” superconductor Pr1.85Ce0.15CuO4 is several times smaller than in the “hole” superconductor La1.85Sr0.15CuO4. The phonon spectrum in Pr1.85Ce0.15CuO4 in the low-energy region is somewhat “more rigid,” and in the high-energy region somewhat “softer” than in La1.85Sr0.15CuO4.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1130935
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  • 5
    Digitale Medien
    Digitale Medien
    Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system (2000)
    Springer
    Physics of the solid state 42 (2000), S. 2177-2183 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al70Pd21Tc9 alloy has a face-centered icosahedral quasi-lattice with parameter a=6.514 Å. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al70Pd21Tc9 sample is measured in the temperature range 3–30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2–300 K. The electrical resistivity is found to be high (600 µΩ cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (γ=0.24 mJ/(g-atom K2)) and the Debye characteristic temperature (Θ=410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1332136
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