Dynamics of Magnetic Fluids in Crossed DC and AC Magnetic Fields.

Alexander Pshenichnikov,Alexander Lebedev,Alexey O Ivanov

doi:10.3390/nano9121711

Alexander Pshenichnikov, Alexander Lebedev + Show 1 more

Open Access

https://doi.org/10.3390/nano9121711

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Abstract

In this study, we derived the equations describing the dynamics of a magnetic fluid in crossed magnetic fields (bias and alternating probe fields), considering the field dependence of the relaxation times, interparticle interactions, and demagnetizing field has been derived. For a monodisperse fluid, the dependence of the output signal on the bias field and the probe field frequency was constructed. Experimental studies were conducted in a frequency range up to 80 kHz for two samples of fluids based on magnetite nanoparticles and kerosene. The first sample had a narrow particle size distribution, low-energy magneto dipole interactions, and weak dispersion of dynamic susceptibility. The second sample had a broad particle size distribution, high-energy magneto dipole interactions, and strong dispersion of dynamic susceptibility. In the first case, the bias field led to the appearance of short chains. In the second case, we found quasi-spherical clusters with a characteristic size of 100 nm. The strong dependence of the output signal on the particle size allowed us to use the crossed field method to independently estimate the maximum diameter of the magnetic core of particles.

Highlights

The behavior of magnetic fluids in crossed magnetic fields (direct current (DC) bias H0 and alternating h = a cos ωt) features a number of peculiarities, which provide valuable information on the internal structure of colloidal solutions, including the characteristic sizes of particles and clusters
This paper presented the results of experimental and analytical investigation into the dynamics of the magnetic fluid in crossed fields
We examined a situation in which the constant magnetic field H0 directed along the sample and the weak alternating field normal to its axis act on the sample of magnetic fluid in the form of the long cylinder

Summary

Introduction

To compare the experimental results, the magnetic moments m of the particles and the Langevin susceptibility χL of the model fluids were considered identical to those of samples No 1 and 2 in Tables 1 and 2. Sample No 2 had a broad particle-size distribution (Table 1) with a long tail, so the main contribution to the dynamic susceptibility was due to the Brownian particles with a magnetic core diameter x > x* and long relaxation times.

Results

Conclusion