Hall magnetometry measurements of bulk single crystalline rings of YBa2CU3O7

The I-V characteristics of YBa2Cu3O7 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 TG. 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 I-V 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 0.006 G/root Hz in a field of I T, corresponding to a relative resolution of I x 10(-6) and a magnetic moment of 5x10(-13) emu. [S0163-1829(98)08237-X].