Magnetic nanoparticle detection using nano-SQUID sensors

摘要

We demonstrate detection of a single core-shell magnetite-silica nanoparticle (outer diameter approx120 nm, moment approx10~(4) (mu)_(B)) using an Nb dc superconducting quantum interference device (SQUID) with the loop size of 350 nm operational at T < 10 K. The system noise was minimized down to 0.2 (mu)(PHI)_(0) Hz~(-1/2) using a cryogenic SQUID series array pre-amplifier. Initial measurements of an individual magnetic nanoparticle were performed and a clear change of the noise spectra of the nano-SQUID was detected at low frequencies in the presence of the nanoparticle. Similar behaviour was confirmed with an FePt nanoparticle with a larger magnetic moment (diameter approx150 nm, moment approx10~(6) (mu)_(B)). Thus, we demonstrate a magnetic sensor based on a dc nano-SQUID and enabling detection of small moments (potentially down to a few electron spins). Such a sensor is of considerable significance for nanomagnetic metrology and quantum information processing based on spin systems.