Ko Yasukochi

Antiferromagnetism of Disilicides of Heavy Rare Earth Metals

Magnetic properties of disilicides of Gd, Tb, Dy, Ho, and Er have been investigated at temperatures ranging from 4.2°K to room temperature. All the disilicides except ErSi 2 have the orthorhombic ThSi 2 type of crystal structure and are shown to be antiferromagnetic. The Neel temperatures of GdSi 2 , TbSi 2 , DySi 2 and HoSi 2 are 27°K, 17°K, 17°K, and 18°K, respectively. The compound ErSi 2 has the hexagonal AlB 2 type of crystal structure and is paramagnetic at above 4.2°K. The paramagnetic Curie temperature of these compounds decreases with the number of f electrons of the rare earth ion.

EFFECT OF EXTERNAL CURRENT ON THE MAGNETIZATION OF NON-IDEAL TYPE II SUPERCONDUCTORS

The influence of the external current on the magnetization of non-ideal type II superconductors is explained. It is shown how in the mixed state the external current brings about a particular state of the critical distribution of flux threads allowing a finite total transport current. In the case where the external current is perpendicular to the external magnetic field, the reduction of the magnetization due to the external current and its dependence on the history of the application of current and field are explained quantitatively in Nb-Zr(25%) alloy. The transverve paramagnetic effect observed by LeBlanc is also discussed.

Magnetization, Flux Flow Resistance and Hall Effect in Superconducting Vanadium

The magnetization, the flux flow resistivity and the Hall voltage have been measured for three vanadium specimens with different purities. The parameters pertinent to the magnetic properties of type II superconductors near the upper critical field H c 2 –the Ginzburg-Landau-Maki parameters κ 1 and κ 2 , and the Helfand-Werthamer parameters h * and (d h /d t )–were obtained from the data. It was found that the values of κ 1 , κ 2 and h * at 0°K increased with increasing purity and the magnitude of the increase of them was larger than the value expected from the microscopic theory. This discrepancy between experiment and theory seems to correspond to the effect of the non-spherical Fermi surface suggested by Hohenberg and Werthamer. Resistivity measurements showed that with increasing purity, the behavior of the slope of the flow resistivity near H c 2 changed from that of the dirty material predicted by Caroli-Maki to that of intermediate material. This result is different from the Kims empirical relation...

Cubic to Tetragonal Transformation in CsCl Type Rare Earth Thallium Compounds

From X-ray powder diffraction measurements, the CsCl type compounds of rare earth elements with thallium have been shown to undergo a cubic to tetragonal phase transformation with decreasing the temperature. The transition proceeds very gradually with temperature and the co-existence temperature range of the cubic and the tetragonal phase spreads over about 200 K for each compound. The temperature T c at which the transformation starts is well defined. The highest value of T c is 300 K for GdTl. The compound LaTl shows no transformation down to 8 K.

Magnetic Properties of Superconducting Tantalum-Niobium Alloys

The superconducting properties of Ta-rich Ta-Nb alloys have been investigated by magnetization measurements. The Ginzburg-Landau parameter κ of pure tantalum is estimated to be 0.42 and the critical value \(\kappa{=}1/\sqrt{2}\) is attained at a composition Ta–2.4 at. % Nb. The dependence of the thermodynamic critical field on temperature T follows the BCS prediction and all the alloys are considered to be weak-coupling superconductors. The lower critical field accords with the microscopic theory in the vicinity of the transition temperature T c , but the discrepancy between experiment and theory increases with decreasing T . The temperature dependence of the upper critical field and the generalized Ginzburg-Landau parameter κ 2 is stronger than the prediction and the disparity becomes large as the electron mean free path l increases. These properties may be ascribed to the effect of the anisotropy of the electronic structure in the state where the electron mean free path l is considerably larger than the...