Magnetic phase ordering in ferrogels under applied field

A new cross linked polymer compound (hydrogel) with fine Fe3O4-grains embed ded in it has been investigated by neutron scattering. We studied the nanos cale structures of these ferrogels synthesized in a magnetic field and with out a magnetic field. By means of polarized neutron scattering we studied t he self-assembly of the particles under the influence of the magnetic field . Even in a weak field (H similar to 65 Oe) the ferrogel showed strong spat ial correlations of the particles; a strong held (H similar to 4 kOe) induc ed slow growth of the interference effect. Over the observation time (sever al tens of hours) a cluster formation of particles was observed. This magne tic ordering is reversible: it disappears when switching off the external f ield. (C) 1999 Elsevier Science B.V. All rights reserved.