CHARACTERISTICS OF DIRECTLY-COUPLED HIGH-T-C SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE MAGNETOMETERS FOR MULTICHANNEL APPLICATIONS

We have characterized directly-coupled de superconducting quantum inte rference device (SQUID) magnetometers for multichannel applications. Y Ba2Cu3O7-delta single layers were deposited on 1 cm x 1 cm SrTiO3 bicr ystal substrates by laser ablation and patterned by Ar ion milling. Fr om the comparison of the experimental data with the theoretical predic tions, we have shown that the degradation of the modulation voltage is caused by the thermal noise Aux and thermal noise rounding in the I-V curve. In addition, the SQUID noise at low frequencies could be expla ined well by critical current fluctuations of the Josephson junctions with a value of S-IO/I-O(2) approximate to (1-4) x 10(-8)/Hz. We have achieved a magnetic field noise of 170 fT/root Hz at 1 Hz. We demonstr ated the use of our magnetometers to obtain realtime traces of a magne tocardiogram inside a magnetically shielded room.