A method for measuring magnetic moment of a single magnetic particle by observing its Brownian motion in a water droplet

Abstract

This study proposes a method for determining the magnetic moment of a single magnetic particle without knowing its shape and size. The studied particle was trapped near the bottom of a droplet, located above a permanent magnet. Its Brownian motion was observed using dark-field microscopy. The magnetic moment of the particle was determined by analyzing the change in the mean horizontal displacement of the Brownian particle from the bottom of the droplet as a function of the magnetic gradient. We measured the magnetic moment of a single nickel particle chosen from particles that have a mean diameter of 0.8 μm by trapping it near the bottom of a suspended water droplet and recording its trajectory for 15 min. The obtained value of the magnetic moment was then compared with the value calculated using the shape of the particle taken with a scanning electron microscope and the data from literature for volume magnetization.