Apparatus for vortex dynamics studies in high T<SUB>c</SUB> samples using close cycle refrigerator and rf oscillators

The design, fabrication, and performance of an apparatus for measurements of rf penetration depth in superconducting samples are described. The instrument makes use of a close-cycle helium refrigerator and is capable of measuring vortex dynamics in superconducting sample of volume as small as 1&#215; 10-3 cm3 with a signal-to-noise ratio of 1400. The system has been tested for a tunnel diode oscillator and an IC 74LS04 oscillator in the 3-5 MHz frequency range. Both magnetic field magnitude and angular variations to the resolution of 1 G and 0.05 &#176;, respectively, are possible with the apparatus. The system performance is evaluated by measuring the dynamical behavior of vortices in platelet samples of Bi2Sr2CaCu2O8 and (Bi-Pb)2Sr2Ca2Cu3O10 superconductors