INTERACTIONS BETWEEN SINGLE-DOMAIN PARTICLES

We present a variation of the Wohlfarth-Henkel technique for studying interactions in single domain particles (SDPs) in which samples are pr epared in different remanent states before the remanent magnetization curves are measured. By analyzing the resulting series of switching fi eld distributions (SFDs), it is possible to separate the effects of po sitive (magnetizing) and negative (demagnetizing) interactions, even w hen one type dominates the other. The method is applied to two types o f samples consisting of uniform SPDs of magnetite produced by magnetot actic bacteria: (1) whole bacterial cells containing single, linear ch ains of SDPs; and (2) SDPs extracted from the cells and allowed to agg regate into clumps.