We report on the development of highly sensitive SQUIDs featuring sub-micrometer loop dimensions. The integration of high quality and low capacitance SIS Nb/AlO x /Nb crosstype Josephson tunnel junctions results in white flux noise levels as low as 66 n 0 /Hz 1/2 , well below state-of-the-art values of their Nb-based counterparts based on constriction type junctions. Estimation of the spin sensitivity of the best SQUIDs yield S  1/2 < 7 B /Hz 1/2 in the white noise region, suitable for the investigation of small spin systems. We discuss fabrication challenges, show results on the electrical characterization of devices with various pickup loops, and describe options for further improvement, which may push the sensitivity of such devices even to single spin resolution. _____________________________________________________________________________________________

Using a commercially available anisotropic magnetoresistance (AMR) sensor of HMC1001, we developed a sensitive magnetometer. It could operate in amplifier mode or feedback mode. The magnetic field sensitivity of the AMR sensor was about 3.2 mV/V G. When the AMR sensor was biased by a voltage of 24 V, the magnetic field resolutions of the AMR magnetometer were about 12 pT/square root(Hz) at 1 kHz and 20 pT/square root(Hz) at 100 Hz. We used the AMR magnetometer for Eddy-current nondestructive evaluation in unshielded environment.

We have investigated the performance of a normal conducting transfer coil (n-coil) for nondestructive evaluation with a SQUID. The transfer efficiency, which depends on frequency and wire impedance, has been calculated for several coil designs to determine the performance of the n-coil. We have fabricated a 30 mm diameter n-coil and examined its performance with a high-TC SQUID. If both the pick-up coil and the input coil have 50 turns, then at high frequencies the magnetic field produced by the input coil becomes 50% of the magnetic field at the pick-up coil, with a low cut-off frequency of 2 kHz. The experimental result agrees well with a numerical calculation, which suggests a magnitude of magnetic field detected by our SQUID equal to the magnitude of the quasi-uniform magnetic field produced by the input coil. We also confirmed that the thermal noise of the n-coil, produced by its normal resistance, does not become higher than the intrinsic magnetic field noise of the SQUID.

No abstract

A four-channel YBa2Cu3O7−y thin film dc SQUID magnetometer was fabricated. Biomagnetic measurements were performed by using the four-channel system at 77 K in a magnetically shielded room. We have successfully measured four-channel magnetocardiac signals clearly in real-time mode. The best magnetic field resolution of the four SQUIDs was 370 fT/Hz1/2 at 10 Hz and 200 fT/Hz1/2 in the white noise region.