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SEM image of a single FePt particle bead positioned at the Nb nano-SQUID perimeter. In the experimental setup the applied dc magnetic field perpendicular to the SQUID loop (geometric area is ), whereas the effective area from measured flux period is . Thus, the penetration depth appears but this ignores flux focusing/defocusing.
(a) Schematic circuit diagram showing nano-SQUIDs (in the dotted line box) and SSA as preamplifier in two-stage configuration, where is the bias resistance. (b) Cold stage of the measurement probe with a SSA chip, superconducting coil and nano-SQUID chip (located inside the coil).
(a) SQUID output at 7.8 K with no particle present (the thin line is field sweep up, thick line is field sweep down). (b) SQUID output with a single FePt nanobead present at same temperature showing hysteresis.
(a) Hysteresis plots for the single FePt nanobead for a range of applied magnetic fields. (b) Magnetization measurements of a large ensemble of FePt beads of various sizes at different temperatures, indicating the blocking temperature, , at about 10 K.
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