Optimization of an AC/DC High- SQUID Magnetometer Detection Unit for Evaluation of Magnetic Nanoparticles in Solution

We have optimized the detection unit of a previously developed AC/DC magnetometer that employs a high critical temperature superconducting quantum interference device high-T_c SQUID. Optimization involves improvement of the usable dynamic range of the high-T_c SQUID system during excitation with an AC magnetic field using a tuned compensation coil and an increase in the DC magnetic field resolution using a secondary excitation coil. The compensation coil technique had resulted in a single and compact detection coil using one SQUID for both AC and DC magnetization measurement functions with improved sensitivity in AC measurements. The sensitivity of the improved system is demonstrated by measuring the magnetization curve and harmonics distribution of low-concentration iron oxide nanoparticles solutions. Highly sensitive evaluation of magnetic nanoparticles in solutions can be expected with the developed system.