Modeling of magnetization dynamics and thermal magnetic moment fluctuations in nanoparticle-enhanced magnetic resonance detection

This study presents a systematic numerical modeling investigation of magnetization dynamics and thermal magnetic moment fluctuations of single magnetic domain nanoparticles in a configuration applicable to enhancing inductive magnetic resonance detection signal to noise ratio (SNR). Previous proposals for oriented anisotropic single magnetic domain nanoparticle amplification of magnetic flux in a magnetic resonance imaging (MRI) coil focused only on the coil pick-up voltage signal enhancement. In this study, the numerical evaluation of the SNR has been extended by modeling the inherent thermal magnetic noise introduced into the detection coil by the insertion of such anisotropic nanoparticle-filled coil core. The Landau-Lifshitz-Gilbert equation under the Stoner-Wohlfarth single magnetic domain (macrospin) assumption was utilized to simulate the magnetization dynamics due to AC drive field as well as thermal noise. These simulations are used to evaluate the nanoparticle configurations and shape effects on enhancing SNR. Finally, we explore the effect of narrow band filtering of the broadband magnetic moment thermal fluctuation noise on the SNR. It was observed that for a particular shape of a single nanoparticle, the SNR could be increased up to similar to 8 and the choice of an appropriate number of the nanoparticles increases the SNR by several orders of magnitude and could consequently lead to the detectability of a very small field of similar to 10pT. These results could provide an impetus for relatively simple modifications to existing MRI systems for achieving enhanced detection SNR in scanners with modest polarizing magnetic fields.