Individual observation of Néel and Brownian relaxations in magnetic nanoparticles

Abstract

Magnetic relaxation divided into the Néel and Brownian regimes determines the magnetization dynamics. To develop the signal intensity and resolution of magnetic particle imaging, understanding the magnetization dynamics was required. In this study, the Ne?el and Brownian relaxations were individually evaluated. The two-step magnetization response of magnetic nanoparticles dispersed in a fluid as the Brownian regime occurred after the Ne?el regime was observed by applying a fast responding pulse field. To clarify the magnetic relaxation in detail, it is necessary to individually observe the Ne?el and Brownian relaxations in the superposition system. By fitting the theoretical calculation to the measured time evolution of the magnetization response, we isolated Ne?el and Brownian relaxations from the experimentally observed superposition relaxation system. Moreover, the effect of dipole interactions on Ne?el and Brownian relaxation were confirmed by measuring the dependence of magnetization responses on the particle concentration in a magnetic fluid.

Int. J. Mag. Part. Imag. 6(2), Suppl. 1, 2020, Article ID: 2009005, DOI: 10.18416/IJMPI.2020.2009005