Ching-yao Huang

Transport anomalies and magnetic properties of Sn x Eu1.2?x Mo6S8 alloys

We have measured the resistance R, magnetoresistance, and magnetization of sintered samples of the compounds SnxEu1.2−xMo6S8, where x = 0, 0.12, 0.24, and 0.48. A large resistance anomaly beginning at T ~ 100 K and extending to low temperatures is found in all of the alloys except x = 0.48, which had a high superconducting transition temperature Tc ~ 11.3 K. The resistance anomaly, which appears to be correlated with the depression of Tc, is also correlated with a large negative magnetoresistance at temperatures T ⩽ 12 K. For all samples except x = 0.48, that part of the magnetoresistance attributed to spin-flip scattering is proportional to the square of the magnetization M2 and is 30–40% of R (0) for some samples. Magnetization measurements are consistent with a spin-7/2 paramagnetic behavior of Eu2+ ions when allowance is made for a concentration of 20–30% nonmagnetic (J = 0) Eu3+ ions as determined from Mössbauer measurements. The experimental results are inconsistent with predictions of dilute magnetic alloy Kondo models. We speculate that the resistance anomaly and suppression of Tc for x ⩽ 0.24 are associated with a semiconductor-like behavior.

High pressure study on TiBe2−x Cux and ZrZn2

Abstract The Curie temperature of the itinerant ferromagnets TiBe 2−x Cu x was found to decrease linearly with pressure up to 20 kbar. No sign of superconductivity was detected in TiBe 2−x Cu x and ZrZn 1.9 up to 90 kbar and down to 1.2K. The results are discussed in terms of the model recently suggested by Enz and Matthias concerning the occurence of magnetism and p-state superconductivity in these compounds.

Anomalous temperature dependence of the upper critical fields in magnetic-superconducting Y1−xGdxRh4B4

Abstract We report that the dominant mechanism governing the upper critical field H c2 in Y 1−x Gd x Rh 4 B 4 with x ≥ 0.1 is the magnetic exchange field of Gd spins. The H c2 vs. temperature curve determines the magnetic structure to be of spin glass for x = 0.1 and ferromagnetic for x ≥ 0.2.

Low temperature magnetic and resistive behavior of the (Eu1−xSnx)yMo6S8 system

Magnetoresistance and ac susceptibility measurements have been made on sintered samples of the compounds (Eu1−xSnx)yMo6S8 for x = 0 and 0.1 at y−1.2 and x = 0 and 0.15 at y = 1.0. All samples show negative temperature coefficients of resistance in zero field in the range 4 to 0.02 K. For the pure x = 0 samples the resistance becomes constant below 0.5 K. The magnetoresistance is large and negative for all samples; at 2.4 T and below 0.5 K it is aobut 11% for y = 1.0 and 40% for y = 1.2. For the finite x samples the presence of superconducting second phases made detailed interpretation of the low field resistance data for x = 0.1, y = 1.2 and most of the data for x = 0.15, y = 1.0 somewhat ambiguous. The magnetoresistance saturates for all the samples below 1 K in fields of ∼2 T or greater. The susceptibility of all the samples has a peak near 0.3 K. The resistive behvaior of the samples is characteristic of a magnetic semiconductor. The susceptibility results point to magnetic ordering of the system near ...

High pressure study of the superconducting and magnetic transitions of Er1−xGdxRh4B4

Abstract The superconducting and magnetic transitions were investigated under hydrostatic pressure up to about 19 kbar in the rare-earth rhodium boride ternaries, Er1−xGdxRh4B4, near the critical concentration of Gd above which the superconducting transition is completely suppressed. The superconducting transition temperature remains almost unchanged under pressure for all samples studied. The magnetic ordering temperature is enhanced linearly but at an increased rate as x approaches the critical concentration from below.