Study of magneto-optical properties in magnetic liquids from ac measurements

Lionel Delaunay; Beatrice Payet

doi:10.1117/12.250739

18 September 1996 Study of magneto-optical properties in magnetic liquids from ac measurements

Lionel Delaunay, Beatrice Payet

Proceedings Volume 2782, Optical Inspection and Micromeasurements; (1996) https://doi.org/10.1117/12.250739
Event: Lasers, Optics, and Vision for Productivity in Manufacturing I, 1996, Besancon, France

Abstract

We present an AC original polarimetric method to study `Faraday rotation' of ferrofluids. The studied magnetic liquids are colloidal suspensions of Fe₂CoO₄ ferrite particles dispersed in various solvents. This method is based on an experimental device involving a Faraday modulator positioned between a polarizer and an analyzer with an angular uncrossing of a few degrees. From the detected light intensity we extract the various frequency components V_o, V_f and V_2f where f is the field frequency (h(t) equals H_o.cos2(pi) ft). We consider the origin of the Faraday effect, with AC magnetic fields, in magnetic fluids, as the result of the orientation of the particles towards the field, producing a macroscopic magnetization which can be described by Langevin theory. The theoretical harmonic components V_o, V_f and V_2f are calculated. We show that they depend on the physical characteristics of the magnetic liquids (concentration (phi) , saturation magnetization M_d, mean diameter d of the magnetic particles). They also depend on the amplitude H_o and the frequency f of the AC magnetic field h(t). We also relate the theoretical expression of V_f with the time constant of the Brownian relaxation in the ferrofluids. We compare the theoretical and experimental variations of V_o, V_f and V_2f with H_o and f for various ferrofluids. Finally we mention some applications concerning particles mean diameter and susceptibility measurement and magnetization curves determination.

Citation Download Citation

Lionel Delaunay and Beatrice Payet "Study of magneto-optical properties in magnetic liquids from ac measurements", Proc. SPIE 2782, Optical Inspection and Micromeasurements, (18 September 1996); https://doi.org/10.1117/12.250739

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