High sensitivity magnetization measurements of nanoscale cobalt clusters

Presented is a novel high sensitivity magnetometer allowing us to measure the magnetization reversal of about 104 μB corresponding to a sensitivity of about 10−16 emu. The detector is a niobium micro-bridge DC superconducting quantum interference device (SQUID), fabricated using electron-beam lithography. It is operational in the temperature range of 0–7 K. Furthermore, we present a method to deposit on the SQUID loop a small number of Co clusters of about 2–5 nm in diameter. The first results obtained on these samples show that there is still a ferromagnetic coupling between the clusters and the magnetization reversal takes place by small avalanches.