Measurements of particle size distribution parameters in ferrofluids

Abstract

A method is presented by means of which (for a ferrofluid with a lognormal distribution of particle s i z e ) i t is possible to determine the standard deviation (r) and median particle diameter (D,) from the room temperature magnetisation curve. The method has been applied to several commercial ferrofluids, containing ferrite particles, and to fluids consisting of cobalt particles in toluene prepared by the method of Hess and Parker1. The particle size distributions have also been measured by using an electron microscope. It has been found that the magnetic data gives estimates of the 'magnetic size distribution' parameters Dvm and Cm, which differed from the 'physical size distribution' parameters Dvp and bp obtained from electron microscope data. It is found that Dvp>Dvm, and gp CWm. These observations are consistent with the results of Kaiser and Miskolczy2 and Granqvist and Buhrman'.

Slew-rate dependence of tracer magnetization response in magnetic particle imaging

“…Multiple images (n ¼ 6000 particles) were analyzed to determine size distribution using ImageJ, an open source image processing software developed by the National Institutes of Health. curve and the log-normal size distribution of nanoparticles obtained by fitting the magnetization curve to the Langevin function (Chantrell's method 17 ). Median magnetic core diameter was 24.9 nm (64.6 nm), with r ¼ 0.18, where exp(r) is the geometric standard deviation of the log-normal distribution.…”

A quantitative study of particle size effects in the magnetorelaxometry of magnetic nanoparticles using atomic magnetometry

“…For this reason we have dropped the simplifying assumption and have applied the more complete underlying model given in [30], also known as moment superposition model (MSM) [31]. We will compare the MSM predictions with those of the simplified model for specific particle size distributions.…”

Influence of size distribution and field amplitude on specific loss power

“…This points to the existence of magnetically disordered layer at the surfaces of the particles which do not contribute to the SLP. 23,24 Due to a smaller magnetically active volume, larger size dispersion, lower anisotropy constant and heavy dependence of relaxation rates on these factors, Fe 3 O 4 /PEG6000 shows significantly lower SLP than Fe 3 O 4 /PEG200. The root of these differences between the samples is probably in synthesis conditions, since the coprecipitation technique, while simple and cheap, is hard to control and reproduce.…”