ac susceptibility apparatus for measuring the transition temperature of high-T c crystals, sintered samples, and films

Abstract

We describe a simple ac magnetic susceptibility system which can be used to observe the superconducting transition temperature in the range 4.2–300 K. The apparatus is extremely flexible and has been tested using high‐quality YBa₂Cu₃O_7−x single crystals with volume as small as 2×10⁻⁵ cm³, much larger sintered polycrystalline samples of the same compound, and finally thin films deposited over a surface area of 1 cm². The system measures resonant frequency variations of a parallel LC circuit with the superconductor close to the inductor. Typical frequencies and fields are in the ranges 0.2–10 MHz and 1–2 mG ac in the inductor.