Glass like magnetic alternating field susceptibility behavior of structurally frozen ferrofluids

Four ferrofluids, distinct in size distribution and aggregate structure, we re investigated. The relaxation time tau(m)(T), related to the temperature of susceptibility maximum, was fitted to a Vogel-Fulcher law. A mean orderi ng temperature. T-o, was calculated using magnetic particle parameters deri ved from the structure. It is assumed that at T-o the particle moments of p article clusters correlate, leading to a spin glass-like transition. Hence, then dynamic slows down considerably; as indicated by a strong broadening of relaxation-time distribution. T-o roughly agrees with the energy of comp eting interaction between particle moments, as calculated from the structur e of particle aggregates. Differences between particle arrangements clearly influence the dispersion and absorption, particularly within the cluster p hase.