Magnetic particle structure ordering in ferrogel under applied field

A new cross linked polymer compound (hydrogel) with fine Fe3O4 - grains embedded in it has been investigated by neutron scattering. We studied the nanoscale structures in ferrogels synthesised in a magnetic field and without field. Using the technique of polarized neutron scattering we have studied the self-assembly of particles under applied magnetic field. The hydrogel without any field prepared (degree of swelling similar to 10g/g) showed a significant spatial particle's correlation to be arisen from their dipole coupling even in a weak field H similar to 65 Oe. This is observable as a nuclear-magnetic interference at momentum transfer q similar to 0.1-0.3 nm(-1) corresponding to a characteristic particle's diameter D(p)similar to 30nm. The strong field (H similar to 4 kOe) induces a slow growth of the interference effect. Over the observation time (several 10th hours) the cluster formation of particles was observed. The rate of aggregation is limited by field induced diffusion of particles trapped in the network. This magnetic ordering is reversible: it disappears when switching off the external field,whereas particles structures being more stable remain quite unchanged similar to 6 h after.