Chemical disorder-induced magnetism in FeSi2 nanoparticles

Iron disilicide in a bulk form is practically nonmagnetic. In contrast, nanoparticles of FeSi2 exhibit superparamagnetism with blocking temperatures ranging from 8K(15nm)to34K(55nm). Their relatively low saturation magnetization suggests that the magnetic behavior is associated with only a small fraction of Fe ions, which have a sufficient number of other Fe as nearest neighbors. The chemical disorder is presumably induced in the formation of nanoparticles. A spin glass-type anomaly below 10K observed in specific heat data gives a further evidence for the compositional heterogeneity.