Thin Superconducting Film Characterization by Surface Acoustic Waves.
Research progress rept. 30 Sep 84-30 Sep 85,
WISCONSIN UNIV-MADISON DEPT OF PHYSICS
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Both the dc electrical resistivity and the attenuation of surface acoustic waves SAW were measured in the superconducting state of a granular lead film, as a function of a perpendicular magnetic field. At 4.2 K the film appears to have an upper critical field of about 60 K Gauss. Bulk ultrasonic measurements have been made in the series Er1-xHoxRh4B4. At 15 MHz a broad peak in attenuation, due to a relaxation mechanism associated with the Ho ions, is observed around 10 K. It moves to lower temperatures as x is decreased. An increase in attenuation is observed in the superconducting state of those alloys which are ferromagnetic superconductors. This increase may be due to superconducting screening of crystalline field effects which inhibit spin phonon interaction in the normal state. Preliminary measurements of the acoustoelectric coupling of SAW with an Al granular film, which is held 15 microns above the SAW, indicate that at 19 MHz the attenuation increases when the film becomes superconducting. This is an unexpected result since at this frequency the attenuation is expected to decrease when the film becomes superconducting.
- Electricity and Magnetism