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We propose Superconducting Quantum Interference Filters (SQIFs) as high sensitive magnetic field detectors. The SQIF is made of high critical temperature grain boundary Josephson junctions, and it is surrounded by an on chip superconducting pick-up loop which enhances the magnetic field sensitivity of about 10 times with respect to the same SQIF without pick-up loop. The devices are operated in Stirling microcoolers, at a temperature of about 70 K. In the presence of an applied magnetic field , SQIFs show the typical magnetic field dependent voltage response ( ), which is sharp delta-like dip in the vicinity of zero magnetic field. When the SQIF is cooled with magnetic shield, and then the shield is removed, the presence of the ambient magnetic field induces a shift of the dip position from 0 0 to a value 1 , which is about the average value of the Earth magnetic field, at our latitude. The low hysteresis observed in the sequence of experiments makes SQIFs suitable for high precision measurements of the absolute magnetic field. Typical magnetic flux noise spectra of SQIFs show a white noise level of about 0.6 T Hz. Comparative measurements of the direct spectra with the spectra measured by using noise reduction techniques reveal a significant decrease of the 1 noise levels. The experimental results are discussed in view of potential applications of high critical temperature SQIFs in magnetometry.

We have performed a detailed study of the superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (GBJs). The GBJs were fabricated by the deposition of c-axis oriented epitaxial Bi2Sr2CaCu2O8+x films on SrTiO3 bicrystal substrates. The measured resistive transition R(T), the current-voltage characteristics (IVCs), the temperature dependence of the critical current density Jc(T), and the magnetic field dependence of the critical current Ic(B) of the Bi2Sr2CaCu2O8+x GBJs are similar to those observed for YBa2Cu3O7−δ GBJs. However, for the same misorientation angle the magnitude of Jc is almost an order of magnitude smaller for the BSCCO-GBJs. The R(T) dependencies and the IVCs of the BSCCO-GBJs are close to the prediction of the resistively shunted junction (RSJ) model. The Ic(B) dependencies are close to those of large Josephson junctions with overlap geometry. Our results show that BSCCO-GBJs may be useful for cryoelectronic applications.