T. Jurcut

Magnetic properties of cobalt-strontium-borate oxide glasses

The results of the temperature dependence of the magnetic susceptibility on xCoO{center_dot}(1 {minus} x)[2B{sub 2}O{sub 3}{center_dot}SrO] glasses with 0 < x {le} 50 mol% are reported. The effective magnetic moment values suggest that the Co{sup 2+} ions are predominantly octahedral coordinated in low CoO content glasses, whereas in higher CoO content glasses the Co{sup 2+} ions are located in tetrahedral sites. Also {theta}{sub p} values indicate that the Co{sup 2+} ions participate at the negative superexchange interaction for x {ge} 20 mol%.

SYNTHESIS, MAGNETIC AND TRANSPORT PROPERTIES OF Ru1-xSbxSr2GdCu2O8 COMPOUNDS

Polycrystalline samples with a nominal composition Ru1-xSbxSr2GdCu2O8-d were prepared by a solid state reaction technique. A mixture of RuO2, Sb2O3, Gd2O3, SrCO3 and CuO was used to obtain the samples. We performed X-ray diffraction analyses, DC susceptibility and transport measurements and the studies showed that the samples were almost pure Ru-1212 phase. We also observed that Sb doping reduce the conductivity of the system and the transition temperature decreases with increasing Sb content. This may be due to a distortion of RuO6 octahedral which is responsible for the increase of holes localization.

Transport and magnetic properties in (Bi1.6Pb0.4)(Sr1.8Ba0.2)Ca2(Cu1−xCrx)3Oy bulk

Abstract High- T c cuprates of “Bi-2223” bulk with Cr were prepared by the conventional solid-state reaction method. The samples have been investigated by electrical resistivity, Hall, Nernst effects, AC susceptibility and thermopower measurements in mixed and normal state. The transport coefficients depend strongly on the Cr contents in the samples. The anomalies are discussed in normal state in the framework of phase separation theory. The experimental data in the mixed state are in agreement with the predictions of the time-dependent Ginsburg–Landau theory.

Magnetic susceptibility study of CoOBi2O3PbO glasses

The X -1 - f(T) of xCoO.(1-x)[Bi 2 O 3 .PbO] glass system (0 < x ≤0.4) are investigated. The μ eff values for x ≤0.01 suggest that Co 2+ ions predominantly octahedrally coordinated, whereas for x ≥ 0.03 the Co 2+ ions are located in tetrahedral sites. For 0.01 < x ≤ 0.03 these two types of coordination simultaneously exist. The paramagnetic Curie temperature indicates negative superexchange interactions between Co 2 + ions for x≥ 0.1.

MAGNETIC FIELD AND TEMPERATURE DEPENDENCE OF THERMALLY ACTIVATED DISSIPATION IN EPITAXIAL THIN FILMS OF YBa2 (Cu1-xZnx)3O7-d

The scaling behavior of the effective activation energy of high-quality epitaxial c-oriented YBa2(Cu1-xZnx)3O7-d thin films has been studied as a function of temperature and magnetic field. For all samples, the effective activation energy scales as U(T, μ0H) = U0(1 - T/Tc)mHn with exponent m = 1.6 ± 0.02 - 1.3 ± 0.02 and the field scaling 1/μ0H and -lnμ0H for thick films and ultrathin films, respectively. The results are discussed taking account of the influence of the Zn substitution on the flux pinning in epitaxial YBa2(Cu1-xZnx)3O7-d thin films.

Magnetoresistivity, seebeck, Nernst and hall effects in the mixed and normal state of (Bi1.6Pb0.4Sr2Ca2(Cu1−xNix)Oy epitaxial films

Abstract Measurements of the ac susceptibility, magnetoresistivity, Seebeck, Nernst, and Hall coefficients in Ni doped (Bi,Pb)2223 superconductors, in magnetic fields between 0 and 5 T, and in the temperature range 5–300 K, are reported. The critical temperatures, the Hall, Nernst and Seebeck coefficients depend strongly on the nickel content. In the mixed state and fluctuation regime these can be explained by Ginsburg - Landau theory. The deviation from linear dependence of μ H −1 = f (T 2 ), n H (T) normal sate can be interpreted in the percolative phase separation theory, and S(T) dependence in the frame of the asymmetric narrow-band theory.

TRANSPORT PHENOMENA IN La2-xBaxCuOy EPITAXIAL THIN FILMS

The (001) oriented thin films of La2-xBaxCuO4+d on SrAlO4 substrates with barium composition x = 0 to 2 were grown by DC sputtering and characterized by X-ray diffraction and resistivity measurement. The films with oxygen composition d=0 showed superconductivity for x between 0.055 and 0.30. For x = 0.15, the superconducting transition was maximized to 4.3 K. When the films had d>0, Tc reached 47 K. These values are higher than those for bulk samples. The depression of Tc around x =0.125 is smaller than that for the bulk samples. The compressive strain expands the c-axis and suppresses formation of the low-temperature tetragonal phase. Both effects result in an increase in the bond length between Cu and the apical oxygen, which is responsible for the enhancement of Tc. The samples with lower residual resistivity show a higher Tc, so we suppose that the Tc enhancement is caused by reduced antiferromagnetic spin fluctuation in the CuO2 planes due to the change in the Cu–O apical bond length.

Transport phenomena in La(2-x)Ba(x)CuO(y) epitaxial thin films

The (001) oriented thin films of La(2-x)Ba(x)CuO(4+d) on SrAlO4 substrates with barium composition x = 0 to 2 were grown by DC sputtering and characterized by X-ray diffraction and resistivity measurement. The films with oxygen composition d = 0 showed superconductivity for x between 0.055 and 0.30. For x = 0.15, the superconducting transition was maximized to 4.3 K. When the films had d > 0, Tc reached 47 K. These values are higher than those for bulk samples. The depression of T(c) around x = 0.125 is smaller than that for the bulk samples. The compressive strain expands the c-axis and suppresses formation of the low-temperature tetragonal phase. Both effects result in an increase in the bond length between Cu and the apical oxygen, which is responsible for the enhancement of T(c). The samples with lower residual resistivity show a higher T(c), so we suppose that the T(c) enhancement is caused by reduced antiferromagnetic spin fluctuation in the CuO2 planes due to the change in the Cu-O apical bond length.