Eur. Phys. J. B 5, 859-867 (1998)
https://doi.org/10.1007/s100510050512

Static magneto-optical birefringence of size-sorted γ-F_e2O₃ nanoparticles

¹ Laboratoire des Milieux Désordonnés et Hétérogènes, Université Pierre et Marie Curie, Tour 13, Case 78, 4 place Jussieu, 75252 Paris Cedex 05, France
² Laboratoire des Liquides Ioniques et Interfaces Chargées, Université Pierre et Marie Curie, Bâtiment F, Case 63, 4 place Jussieu, 75252 Paris Cedex 05, France
³ Laboratory of Kinetics of Anisotropic Fluids, Institute of Continuous Media Mechanics, Urals Branch of the Russian Academy of Sciences, 1 Korolyov St., Perm 614013, Russia

Corresponding author: ^a rperz@ccr.jussieu.fr

Received: 9 January 1998
Accepted: 5 May 1998
Published online: 15 October 1998

Abstract

Magnetic birefringence experiments under static field are performed on ionic ferrofluid samples based on γ-Fe₂O₃ . A colloidal size-sorting of the particles allows to obtain narrow size distributions. The optical birefringence of the solutions is found positive and can be described by a Langevin formalism. It scales as H² in the low field limit. In the high field limit the particles size dependence of the saturation birefringence is compatible with a surface anisotropy constant erg cm^-2 associated with a particle elongation of 1.25 both coherent with Néel predictions of surface anisotropy in small grains.