Effects of magnetic nanoparticle films on the electrical characteristics of dc superconducting quantum interference devices

Abstract

We evaluated the effects of Fe3O4 magnetic nanoparticle (NP) films on the electrical characteristics of superconducting quantum interference devices (SQUIDs) at 4.2 K to enhance the performance of superconducting circuits. The NP films were formed directly on the SQUIDs. For SQUIDs with 5-nm-NP films, the SQUID inductance increased almost linearly with the NP film thickness, reaching 19.7% at an NP film thickness of 990 nm. An increase in NP size from 5 to 20 nm reduced that in the SQUID inductance. On the other hand, no clear effects on the current–voltage characteristics of SQUIDs were observed for 5- and 10-nm-NP films, while the critical currents of some SQUIDs with 20-nm-NP films were reduced.

Cryogenic ferromagnetic patterns with controlled magnetization for superconducting phase-shift elements

“…The PdNi films were easily patterned to micron-or submicron-scale, compared with the nanoparticle films used in our previous studies. 18,19) To evaluate the effects of the PSE, rectangular tunnel junctions, with PdNi patterns placed at the same height as the junction barrier, were fabricated and tested. Josephson junctions were used to measure the amount of flux induced by the cryogenic ferromagnetic patterns; the flux was determined from the horizontal shift of the main lobe in the I c modulation pattern for the external magnetic field.…”