Seebeck Effect In ρ-Type SnTe Crystals

Preliminary results of the thermoelectric power measuremnts are presented on a few samples of p-type SnTe crystals with and without Mn impurities over the temperature range from 300 to 77 K. As the temperature is decreased, the Seebeck coefficients decrease and tend to rise near at 100 K; the magnetic impurities are found to be ineffective to this enhancement

Liquid Level Indicator for Metal Dewar

A simple liquid level indicator for a metal dewar has been constructed with the use of superconducting elemental Ta and Nb-Ti alloy as well as carbon resistor. Electrical and superconducting properties, repeatability, sensitivity, and a practical operation of the indicator have been investigated at 78°K and 4.2°K. The hysteresis or instability effect of the resistance for Nb-Ti wire was found at the magnetic field of 17 kG. Evaporation rate of liquid helium can be estimated in the dewar with a few indicators

LOW TEMPERATURE NMR APPARATUS WITH MOSFETS (3SK45) AND A1 20 27

Thermal hysteresis tests have been made between 300 and 77 K for the static characteristics of commercial MOSFETs (3SK45) which are to be used as active elements in our steady-state NMR apparatus. The newly constructed apparatus using this type of FETs works well at low temperatures, with respect to the reproducibility, stability, and signal-to-noise ratio. With this device, the A127 NMR in ruby crystal (A1203:cr3+) has been measured at 77 K and liquid helium temperatures. Both the dipolar splitting width and the absorption intensity in the NMR spectrum depend on temperature and the angle between the magnetic field and the trigonal axis. These results are explained by the spin diffusion model, in which the A127 nuclei see the local fields arising from identical nucear spins and the paramagnetic electron spins of cr3+ ions existing in the crystal

Low Field Superconducting Magnet with Nb-Ti Wire

A low-field square ended superconducting magnet has been constructed with Nb-Ti alloy as a coil, which is to be used for the nuclear magnetic resonance experiment at helium temperatures. The wire is wound around a brass bobbin (the inner diameter 10 mm and the length 60 mm). To operate the magnet in a persistent mode, a persistent current switch with the same wire is attached The magnetic field strength at the exciting current 20 A is about 12kG, which is measured by a Bi-sensor. No decay of the persistent current is observed with time. The field strength vs. the current and the field distribution in the magnet are measured, which are in good agreement with the calculated values

Magnetotransport Measurements of η-Mo_4O_<11> Crystals Using a Hybrid Magnet(Transport and Fermiology)

Magnetoresistance and Hall effect have been measured at 4.2 K using a hybrid magnet up to 26 T for several crystals of quasi-two-dimensional η-Mo_4O_ that has a charge-density-wave (CDW) induced nested multiple carrier band structure. The magnetoresistance is exceptionally large and the Hall resistivity shows a unique magnetic field dependence. We have confirmed the existence of characteristic hysteresis phenomena in both quantities when a field-sweep range exceeds a threshold value (?10 T). The hysteresis effects can be related with an effective and magnetic field dependent irreversible process for the CDW formation and destruction. We have also found that the hysteresis and quantum oscillations in the magnetotransport are strongly sample-dependent