Hall magnetometry measurements of bulk single crystalline rings

The (Formula presented) characteristics of (Formula presented) rings are measured down to the subpicovolt level using a Hall magnetometry technique. Non-Ohmic response of the rings to an ac magnetic field is detected below a temperature (Formula presented) Fourier analysis of the data demonstrates appearance of higher harmonics up to order 9. The frequency and amplitude dependence of the harmonic susceptibilities is analyzed. The quasistatic (Formula presented) response of the ring is obtained after using a triangular wave form, providing conclusive evidence for the vortex-glass phase transition in twinned crystals. Different techniques are employed to improve the resolution of the method, including use of different semiconducting materials and use of a bridge circuit. The resolution achieved is (Formula presented) in a field of 1 T, corresponding to a relative resolution of (Formula presented) and a magnetic moment of (Formula presented). © 1998 The American Physical Society.