Experimental study of the effects of interactions on Henkel and △M plots

The magnetic field-dependent remanent magnetization and demagnetization of an isoparaffin-based ferrofluid¹ have been measured as a function of magnetic interaction strength. Samples of this ferrofluid were prepared with varying magnetite concentrations to alter the average particle separation and thus the magnetic interactions. The ferrofluid samples were demagnetized thermally and frozen prior to measurement of the magnetization and demagnetization remanences. The measured magnetization and demagnetization remanences were plotted parametrically in magnetic field magnitude to produce Henkel and △M plots. The Henkel plots for more concentrated ferrofluid samples deviated from the predictions of the Wohlfarth model for non-interacting particles, and were consistent with demagnetizing interactions in the system. The magnitude of this deviation decreased with decreasing magnetite concentration, and the Henkel plot for the most dilute sample agreed with the Wohlfarth model’s predictions. Furthermore, a quantitative model that accounts for deviations from the Wohlfarth model is presented and may be applied to other systems.

1. Liquids Research Ltd., http://liquidsresearch.com/