AC magnetometry with active stabilization and harmonic suppression for magnetic nanoparticle spectroscopy and thermometry

Magnetic nanoparticle (MNP) thermometry based on magnetic particle spectroscopy is explored as a potential approach for realizing in situ temperature measurement of 3D objects. MNP thermometry relies on the nonlinear magnetization response to an AC drive field. This nonlinear response has functional dependence on frequency and temperature, governed by the complex magnetization dynamics of MNPs suspended in solution. In this work, we introduce our approach for accurate and precise AC magnetization measurements using actively stabilized drive fields ranging from direct current to 10kHz. To isolate the harmonic response of MNPs from the drive field, we also perform active cancelation to reach drive field suppression up to 120dB. Active stabilization and cancelation are utilized for real-time, sensitive measurements of AC magnetization of commercial samples, with stability on the timescale of hours. Initial results for MNP thermometry are demonstrated using this technique, and we achieved a total temperature uncertainty of 410mK and 170mK at 100ms and 10s integration time, respectively.