We mounted a vector-scanning superconducting quantum interference device (SQUID) sensor on a commercial SQUID microscope and successfully improved the sensitivity and spatial resolution of the sensor. Our proposed vector 3D SQUID sensor used multilayered niobium (Nb)-based technology; we realized three SQUID sensors in the structure of a vector pickup coil system on a single chip. The vector pickup coil system was built with three pickup coils that were orthogonal to one another to obtain the X, Y, and Z components of a magnetic field vector. To improve both sensitivity and spatial resolution, we attempted to reduce the inner diameter by increasing the number of windings of the pickup coils using the multilayered Nb process. The design value for the dc SQUID sensors was either the critical current density Jc = 320A cm−2 for two Josephson junctions (JJs) or the critical current Ic = 12.8μA for the 2μm × 2μm JJs. To measure the current–voltage (I–V) and voltage–flux (V–Φ) characteristics of a sensor, we constructed a homemade measurement system. The fundamental characteristics of our SQUID sensors were in good agreement with the design parameters. We mounted our vector SQUID sensor on a commercial scanning SQUID microscope (SQM2000, Seiko Instrument Inc.) with a single flux-locked loop channel to test one of the three channels. We repeated the measurements three times to obtain the X, Y, and Z componential images of the magnetic field from a single vortex, and we synthesized the 3D mapping of the magnetic field vectors from a single vortex. We proved that our sensor mounted on a SQUID microscope was suitable for measuring the X, Y, and Z components of a vector magnetic field.

The MgB 2 detector consists of 200 nm thick MgB 2 thin film meander structure of 3 µm line width protected by 300 nm thick SiO layer. The electrical connections were provided by 150 nm thick Nb. The devices were placed in a 4 K refrigerator to investigate the behavior at temperatures below T c . The position-dependent response of the MgB 2 detector can be investigated by scanning a laser spot with the T. Ishida ( ) · I448 J Low Temp Phys (2012) 167:447-454 aid of the XY Z piezo-driven stage and an optical fiber with a focusing lens. We found that the inhomogeneity in a detector is very critical to specify the detection efficiency since the detector has the sensitivity only in a narrow temperature regime near T c .

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