Abstract:
A dynamic probing of magnetic liquids is performed experimentally, using a static magnetic field modulated by another smaller field, normal and alternating. The optical magneto-birefringence under these crossed magnetic fields is recorded as a function of the frequency for different field intensities and different sizes of the magnetic nanoparticles. A general reduced behavior is found for the in-phase and the out-of-phase optical response which is well-described by a simple mechanical model. Depending on the value H ani of the anisotropy field of the nanoparticles, we can distinguish two different high magnetic field regimes: - a rigid dipole regime (large anisotropy energy with respect to k B T) for cobalt ferrite nanoparticles with a relaxation time inversely proportional to the field intensity H C(H C < H ani), - a soft dipole regime (anisotropy energy of the order of k B T) for maghemite nanoparticles with a relaxation time independent of the field intensity H C(H C > H ani).
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Received 5 June 2000 and Received in final form 8 January 2001
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Hasmonay, E., Dubois, E., Neveu, S. et al. Alternating magneto-birefringence of ionic ferrofluids in crossed fields. Eur. Phys. J. B 21, 19–29 (2001). https://doi.org/10.1007/s100510170208
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DOI: https://doi.org/10.1007/s100510170208