Effects of magnetic interactions in antiferromagnetic ferrihydrite particles.

The effects of magnetic interactions in the magnetic properties of six-line ferrihydrite particles were investigated by studying the behavior of aggregated versus coated particles. Four different coating agents (sugar, alginate, lactate and ascorbate) were employed in order to obtain dispersed particles and prevent particle agglomeration; one sub-sample was allowed to dry with no coating agent. The five sets of ferrihydrite particles were from the same batch and the size was estimated as 3.6 ± 0.4 nm in length. Low temperature magnetization, ac susceptibility and Mössbauer spectroscopy data showed contrasting blocking temperatures for uncoated and coated samples with a decrease of T(P) from about 50 K to 12 K, respectively. The contributions from magnetic interactions were recognized in magnetic measurements and the effective anisotropy constant for non-interacting ferrihydrite was estimated as (100 ± 10) × 10(3) J m(-3). Overall, employing sugar and alginate as coating agents was more successful in preventing particle aggregation and magnetic interactions. In contrast, ascorbate and lactate were unsuitable due to the chemical reaction between the coating agent and ferrihydrite surface.