TopPage学生の学会発表 > 04論文

2004 論文

2016/09/13(Tue) 11:04


1: Pressure effect on the magnetic properties of Ce(Fe1-xCox)2
Okada, H; Koyama, K; Miura, S; et al.

We have studied the magnetic properties of Ce(Fe1-xCox)2 with x less than or equal to 0.1 by magnetization measurements under high pressures up to 1.2 GPa. In pure CeFe2, the Curie temperature T-C decreases, and the saturation magnetization M-s is suppressed by applying pressure. In Co substitution compounds, the transition temperature T-A from the ferromagnetic (FM) to the antiferromagnetic (AFM) states and the metamagnetic transition field B-c increase with increasing pressure, while T-C and the magnetization of the spontaneous and field-induced FM states decrease. The obtained results indicate that the AFM state becomes stable by the lattice contraction.

2: Two-step structural modulations and Fermi liquid state
  in spinel compound CuV2S4

Okada, H; Koyama, K; Watanabe, K

We have studied the magnetic, transport and structural properties of chalcogenide spinel compound CuV2S4 using a high-quality polycrystalline sample, in order to clarify the intrinsic physical properties of CuV2S4. The magnetic susceptibility and the electrical resistivity exhibit two sharp anomalies. One is reversible for temperature T-t1 = 91.5 K and the other shows a thermal hysteresis of about 4 K at T-t2 = 56 K. We clearly observed for the first time that both anomalies are accompanied with two-step structural modulations. The crystal structure changes the symmetry form cubic to tetragonal at T-t1, and then the lattice constant is modulated discontinuously at T-t2 without changing the symmetry. In addition, the paramagnetic susceptibility is very large, and the electrical resistivity at low temperatures shows a quadratic temperature dependence with the coefficient A = 0.05 muOmega cm/K-2, which is larger than that of conventional metals. These results indicate that CuV2S4 exhibits a Fermi-liquid-like behavior with strongly correlated electrons at lower temperatures.

3: E-J Properties of Bi2Sr2CaCu2O8 Thick Films
K. Takahashi, S. Awaji, G. Nishijima and K. Watanabe
SPhysica C 412-414 (2004) 1041-1044.

In order to evaluate the effect of the microstructure on E-J properties, the E-J properties for Bi2212 thick films prepared under three different conditions were measured. The measured E-J properties were analyzed based on the percolation model, and the local J(c) (J(cl)) distribution was evaluated. The distribution of the local J(c) was much affected by its micro structures. For the well aligned sample with large plate-like grains, which is similar to Ag-sheathed Bi2212 tape, the distribution of the local J(c) at percolation transition field B-GL was found to be asymmetric and reached the high J(cl) region.

4: Bi2Sr2CaCu2Oδ厚膜の電界 − 電流密度特性に及ぼす微細組織の影響
高橋健一郎、淡路 智、西島 元、渡辺和雄
Forum of Superconductivity Science and Technology News (FSST NEWS) No.102 4-6.

5: CuNb/Nb3Sn超伝導線材の超伝導特性に与える事前曲げ歪みの効果
小黒英俊、西島 元、淡路 智、渡辺和雄
低温工学 39 (2004) 422-426.

In order to develop a Nb3Sn coil using a react and wind method, it is important to clarify the influence of bending strain because the superconducting characteristics of Nb3Sn are very sensitive to stress and strain. We investigated the effect of prebending strain εpb, which means repeated bending loads, from 0% to 1.5% for superconducting wires. We found that Ic, Tc and Bc2 were enhanced by prebending strain. When the prebending strain was 0.8%, Ic values showed maximum enhancement at a whole magnetic field for CuNb/Nb3Sn wires. For instance, Ic was approximately twice at 19 T. Bc2 increased about 1.5 T at a whole temperature when εpb was 1.0%. Tc increased from 17.5 K to 17.9 K at a prebending strain of 1.2%.