Alternating magneto-birefringence of ionic ferrofluids in crossed fields E. Hasmonay, E. Dubois, S. Neveu, J.-C. Bacri and R. Perzynski Eur. Phys. J. B, 21 1 (2001) 19-29 Published online: 15 May 2001 DOI: 10.1007/s100510170208