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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5567-5569 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The irreversibility lines of Pr-doped Br2Sr2Ca1−xPrxCu2Oy single crystals have been studied systematically. It was found that for the Pr-doped samples as compared with the undoped Bi2Sr2CaCu2Oy the effective superconducting area shrinks, the irreversibility line Birr decreases, and the anisotropic parameter γ increases strongly due to Pr doping. It is evident that the substitution of Pr for Ca in the system effectively reduces the hole concentration on CuO2 layers to the underdoped state and destroys the Josephson coupling of the two superconducting regions of adjacent CuO2 layers. The vortex depinning is responsible for the irreversibility and the displacement value for vortex depinning is similar to that for vortex lattice melting, but with different physical meaning. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1406-1410 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: La0.67Ca0.33Mn1−xCuxO3 (x=0 and 0.15) epitaxial thin films were grown on the (100) LaAlO3 substrates, and the temperature dependence of their resistivity was measured in magnetic fields up to 12 T by a four-probe technique. We found that the competition between the ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases plays an important role in the observed colossal magnetoresistance (CMR) effect. Based on a scenario that the doped manganites approximately consist of phase-separated FM and PI regions, a simple phenomenological model was proposed to describe the CMR effect. Using this model, we calculated the resistivity as functions of temperature and magnetic field. The model not only qualitatively accounts for some main features related to the CMR effect, but also quantitatively agrees with the experimental observations. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1217-1217 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A large diameter intense beam current broad beam ion source used for surface modifications is described. It consists of a discharge chamber and a three-grid extraction system. The discharge chamber has two anodes (front and rear) and a specially designed cusped magnetic field is used for forming a large field free region in the chamber so that a very uniform and intense ion beam has been extracted from this source. Beam currents of more than 900 mA for hydrogen and 750 mA for argon at 2.5 kV extraction voltage have been obtained. The highest beam current density is over 2.5 mA/cm2, measured at a location 25 cm downstream of the source. The density uniformity changes from +5% to +15% over a 15-cm-diam circle. The feature and the performance of this source will be described in this paper. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 924-926 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: This paper describes a new type of electron beam evaporation intense beam current broad beam metal ion source. In this ion source, a focusing electron beam is used to bombard and vaporize the metal and other solid elements within the same chamber where the metal and solid element atoms are ionized by arc discharge. It can operate with gaseous and solid elements. Both pure or mixed ions with single or multiple charge states can also be extracted from this source. The performance and the characteristics of this source have tested. Ion beams of a series of elements, which include C, W, Ta, Mo, Cr, Ti, B, Cu, Ni, AI, Ar, N, etc., have been extracted, and the highest beam current is up to 90 mA. By using this ion beam bombardment, a good mixture between substrate and film was observed. Deposition rates as high as 25 A(ring)/s for Mo, 30 A(ring)/s for Ti, and 80 A(ring)/s for C have been obtained. The structure of the ion source and the experimental results will be presented in this paper. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 3871-3875 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Oxidation of Fe ultrafine particles has been studied in air at temperatures ranging from 300 to 873 K. It is found that γ-Fe2O3 and α-Fe2O3 are formed at different temperatures, which leads to significant changes in the particle features and magnetic properties. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3006-3010 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A comparative study of the effect of annealing in reduced oxygen pressure on the electrical transport properties of (La1−xNdx)0.7Sr0.3MnO3 (x=0, 0.25, 0.5, 0.75, and 1) epitaxial thin films and bulk materials has been carried out. The epitaxial films grown by pulsed laser ablation were in situ annealed in an oxygen atmosphere of 2×10−6–760 Torr at 700 °C for 1 h. It is found that the electrical transport behavior of the epitaxial film is insensitive to the annealing pressure. A similar thermal treatment on the bulk materials at 5 mTorr oxygen ambient, however, caused a dramatic change in their resistivity-temperature dependence. Our results suggest that the annealing has a prominent effect on the properties of grain boundary, which plays an important role in determining the electrical transport behavior of polycrystalline manganites. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1867-1873 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ni–Co ultrafine particles (UFPs) were prepared by hydrogen plasma metal reaction. Particle characteristics, oxidation, and magnetic properties were investigated and compared. fcc structured Ni–Co UFPs with a sphere shape were prepared over the whole composition range. The particles distribute from 5 to 100 nm in size with an average particle size of about 35 nm. They are thermally stable in air below 433 K, but oxidize quickly at the higher temperatures. The saturation magnetization of the UFPs is lower than that of the corresponding bulk alloy, especially in the Co rich side. Formation of oxide layer on the particle's surface is an important reason for this reduction. Ni–Co UFPs possess large residual magnetization and coercive force above 60% Co. The composition dependence of the saturation magnetization and the coercive force changes remarkably around 60% Co, which implies a large variation in magnetic status around this composition. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2422-2424 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Differential scanning calorimetry and x-ray diffractometry have been used to monitor reactions of the C15 Laves phase GdCo2 during constant-rate heating in a hydrogen atmosphere and to determine the enthalpy change of each reaction. The values of the enthalpy change ΔH of hydrogen absorption, hydrogen-induced amorphization and crystallization are evaluated to be −67.2, −10.2, and −9.8 kJ/mol Gd, respectively. On the other hand, ΔH of hydrogen desorption is +31.4 kJ/mol Gd. The amorphous a-GdCo2Hx alloy crystallizes to GdH2 and Co. Therefore, the total value of ΔH of the above reactions along with the formation of GdCo2, −103 kJ/mol Gd, becomes nearly equal to that of formation of GdH2, −101 kJ/mol Gd.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1173-1175 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The longitudinal and transverse ultrasonic velocities and attenuations, the transport and magnetic properties, as well as the structural changes of polycrystalline La0.25Ca0.75Mn0.93Cr0.07O3 have been studied systematically. A velocity minimum and an attenuation peak for both longitudinal and transverse waves occur around the temperature Tco of charge ordering transition accompanied by the structural change from a cubic to a tetragonal phase. Near temperature TN (where the c-axis length shows a maximum), the sharp decrease of velocities for both waves and the appearance of a longitudinal attenuation peak are attributed to the antiferromagnetic transition together with the anomalous change in c-axis length of the tetragonal phase. The simultaneous occurrence of the ultrasonic, lattice, charge ordering, magnetic, and transport anomalous characteristics indicates the strong electron–phonon and spin–phonon interactions in the system. © 2000 American Institute of Physics.
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3088-3090 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The Gd and oxygen doping effects on the Josephson coupling in Bi2Sr2Ca1−xGdxCu2O8+δ single crystals have been studied systematically. It was found that a pseudo-transition at temperature TcJ, attributed to the Josephson coupling between CuO2 layers, shifts dramatically to lower temperature with increasing magnetic field, and the temperature dependence of the pseudo-upper-critical-field HcJ associated with the coupling shows a clear upward curvature. For the Gd-doped as compared with the oxygen-doped crystal, the value of TcJ is smaller at the same carrier density, which implies that the substitution of Gd for Ca reduces the Josephson coupling more severely. The characteristics of the pseudo-transition associated with the Josephson coupling between CuO2 layers are different from those of the superconducting transition occurring in the CuO2 layers. © 2000 American Institute of Physics.
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