Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field.
Superparamagnetic iron oxide nanoparticles with highly nonlinear magnetic behavior are attractive for biomedical applications like magnetic particle imaging and magnetic fluid hyperthermia. Such particles display interesting magnetic properties in alternating magnetic fields and here we document experiments that show differences between the magnetization dynamics of certain particles in frozen and melted states. This effect goes beyond the small temperature difference (ΔT~ 20 °C) and we show the dynamics to be a mixture of Brownian alignment of the particles and Néel rotation of their moments occurring in liquid particle suspensions. These phenomena can be modeled in a stochastic differential equation approach by postulating log-normal distributions and partial Brownian alignment of an effective anisotropy axis. We emphasize that precise particle-specific characterization through experiments and nonlinear simulations is necessary to predict dynamics in solution and optimize their behavior for emerging biomedical applications including magnetic particle imaging.
Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA ; Department of Physics, Forman Christian College (University), Lahore, Pakistan.
Saqlain A
SA
Shah
Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA.
Daniel B
DB
Reeves
LodeSpin Labs, P.O. Box 95632, Seattle, Washington 98145, USA ; Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
R Matthew
RM
Ferguson
Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA ; Department of Radiology, Geisel School of Medicine, Hanover, New Hampshire 03755, USA.
John B
JB
Weaver
Materials Science and Engineering, University of Washington, Seattle, Washington 98195, USA.
Kannan M
KM
Krishnan