Measurement of Magnetic Nanoparticles Using High Transition Temperature Superconducting Quantum Interference Devices

Superconducting quantum interference device (SQUID) based sensors hold promise for magnetic detection of magnetically tagged biological cells. In this work, a high transition temperature (high-T C ) direct-coupled SQUID micro-magnetometer was fabricated from a 30-nm-thick YBa 2 Cu 3 O 7-δ (YBCO) thin film. The SQUID was directly written with irradiation from a finely focused helium ion beam without milling or etching any material. An experiment estimating the sensitivity of the magnetometer to magnetic nanoparticles was conducted that revealed the magnetic moment calculated based on the measurement of the SQUID magnetometer is consistent to that obtained from susceptibility measurements.