HTS SQUID microscope head with sharp permalloy rod for high spatial resolution

Features of amplification of dipole magnetic field with linear ferromagnetic concentrator

“…These dependences were used to calculate the amplification A with different LFCs. The dependences A͑L͒ for the minimum and maximum magnetic moments M G of the coil at different LFC diameters and two frequencies f =10 3 Hz and f =10 4 Hz are illustrated in Fig. 3.…”

“…Finally, Fig. 5 demonstrates the dependences of the voltage in the detecting coil upon the magnetic moment M G of the LFC at the frequency f =10 4 Hz for two LFC diameters and three LFC lengths. It is seen that the dependence V͑M G ͒ remains linear in the whole range of M G values for the LFC with d = 0.3 mm.…”

“…The use of LFC in ͓conjugation with a SQUID-based detector provides the maximum amplification and rules out extra LFC-induced magnetic noise in the region near the SQUID detector. Subsequent investigations by other researches 4,5 lent more evidence in favor of this approach.…”

“…The coil was wound on one of the LFC ends ͑generating coil, G͒. The frequency of the alternating current I in the coil was f =10 3 Hz or f =10 4 Hz. The current varied from 10 −3 to 5 ϫ 10 −2 A.…”

SQUIDs: microscopes and nondestructive evaluation

“…This allows for quick sample changes, but the thickness of the window limits the minimum stand-off distance between SQUID and sample -and thus the spatial resolution -to about 50 µm. One can use a SQUID made from so-called high temperature superconductor (HTS), such as YBa 2 Cu 3 O 7 , cooled to liquid nitrogen temperature in order to reduce costs for the coolant, [5][6][7][8][9] or a LTS SQUID offering a lower flux noise [10,11]. By cooling the SQUID to 4.2 K and having the sample at room temperature, a spatial resolution of still better than 100 µm can be achieved.…”