Yuko Nakamori

Magnetic and electrical properties of the intermetallic compounds R7Rh3 (R=La, Ce, Pr and Nd)

Abstract Magnetic and electrical properties of the hexagonal Th 7 Fe 3 -type R 7 Rh 3 compounds (R=La, Ce, Pr and Nd) have been studied by measuring a.c. magnetic susceptibility, magnetization, electrical resistivity, thermoelectric power and thermal expansion for polycrystalline samples. The Ce 7 Rh 3 and Pr 7 Rh 3 show ferromagnetic ordering below 6.8 and 15.6 K, respectively. In Nd 7 Rh 3 , there are two magnetic ordered phases; the ferromagnetic phase below 11 K and the antiferromagnetic phase up to 32 K. In the antiferromagnetic phase, a metamagnetic transition takes place. Pronounced changes at the magnetic transitions are observed in thermoelectric power.

Synthesis of the binary intermetallic superconductor MgB2 under hydrogen pressure

Abstract The binary intermetallic superconductor MgB 2 was synthesized for the first time under a hydrogen atmosphere of 1.0 MPa. The synthesis reaction between elemental Mg and B was completed after only 10 min at 1173 K (about 4 h over 1000 K). The particle size of the sample synthesized in this way is comparable to that of the elemental Mg used as a starting material, while in a sample synthesized under an argon atmosphere the particle size is drastically decreased by cracking during the synthesis of MgB 2 . Hydrogen solubility was estimated to be less than 0.01 mass% at around room temperature. However, the lattice constant a is nearly 0.1% larger and thus the critical temperature for the superconductivity T c is ∼0.6 K higher in the sample synthesized under hydrogen than in the sample synthesized under argon. Therefore, the synthesis under hydrogen is a promising process to optimize the superconducting properties of MgB 2 and related systems.

Difference in the transport properties between Y7Rh3 and La7Rh3

Abstract Transport, thermodynamic and magnetic properties in La7Rh3 and Y7Rh3 were examined. The results indicate that La7Rh3 is metallic and becomes superconducting below 2.5 K . In contrast, Y7Rh3 shows anomalous transport properties with a broad maximum around 200 K and a negative temperature coefficient of electrical resistivity at higher temperature. The number of carrier in Y7Rh3 is less than that in La7Rh3, while the electron correlation of Y7Rh3 is stronger than that of La7Rh3. Thus the contrastive physical properties between light- and heavy-rare-earth R7Rh3 might be originated in both the difference of the number of carrier and strength electron correlation owing to change in the lattice constants.

Specific heat of CeMg2Cu9 with a two-dimensional Ce arrangement

Abstract We have carried out the specific heat measurements under pressures between 0 and 0.91 GPa on CeMg2Cu9, in which the Ce atoms are a two-dimensional arrangement. A large peak is observed at T N =2.5 K for 0 GPa . TN increases below 0.89 GPa , and turns to decrease with pressurization. The released magnetic entropy Sm below TN is about 60% of R ln 2 expected for the twofold spin degeneracy, suggesting Kondo-compensated moments are formed in the low-temperature range.