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.