Magnetic structure of small NiFe2O4 particles

Abstract

The magnetic structure of small NiFe2O4 particles has been investigated. Samples (in the few hundred angstrom size range and up) were prepared by chemical precipitation followed by a heat treatment at relatively low temperatures. Mössbauer spectra of the 57Fe nuclei, obtained with a longitudinal magnetic field applied, unambiguously establish that a non-collinear structure exists. Further, the magnetic moment at low temperatures is appreciably lower than the value reported for bulk material. A model is proposed in which the NiFe2O4 particles consist of a core with the usual spin arrangement and a surface layer with atomic moments inclined to the direction of the net magnetization. The temperature dependence of this structure is also reported.