Neutron depolarization study of the Fe3O4-based frozen ferrofluids

Magnetic properties of the Fe3O4-based frozen ferrofluids (FFF) are investi gated using a neutron depolarization (ND) technique at the temperature rang e from 20 to 290 K and at the magnetic field from SO to 8000A;md The invest igated FFFs (1, 2, 3) with concentration about 10% differ in an average dia meter of the particle (51, 53, 67 Angstrom). with dispersion (0.20, 0.53, 0 .51), respectively. It was found that the ferrofluids frozen in zero magnet ic field can build magnetic dipole glasses with spin-glass-like behavior, e .g. with a long-time relaxation of the magnetization and irreversibility at low temperature. The data can be interpreted in terms of an energy balance of magnetic (dipole interactions, magnetic field) and thermal contribution s. (C) 2001 Elsevier Science B.V. All rights reserved.