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Mössbauer spectra of CoFe2O4 show that this spinel is not completely inverse and that the degree of inversion depends on the heat treatment of the material. The magnetic moments of the slowly cooled and the quenched material are 3.4 and 3.9 μB per unit chemical formula, respectively, and the Néel temperatures are 798°K and 792°K, respectively. From the width and the shape of the absorption lines of the Mössbauer spectra several magnetic hyperfine fields have been identified with different B sites and the temperature dependences of these fields have been determined. The different hyperfine fields have been attributed to 57Fe nuclei in B sites with different ratios of iron and cobalt ions in the six nearest-neighbor A sites.

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Highly zero-biased magnetoelectric response in magnetostrictive/piezoelectric composite J. Appl. Phys. 112, 024504 (2012) Resonance magnetoelectric effects in a layered composite under magnetic and electrical excitations J. Appl. Phys. 112, 014103 (2012) Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillarsThe magnetic structure of small CoFe Z 0 4 particles has been investigated as a function of the particle size. Samples (in the 10-100 nm size range and up) were prepared by chemical precipitation followed by a heat treatment at relatively low temperatures. M6ssbauer spectra of the 57Fe nuclei, obtained with a longitudinal magnetic applied field, unambiguously establish that a noncollinear structure exists that is most pronounced for the smallest particles. The analysis indicates that a surface effect of the crystallites that make up a particle is the origin of this phenomenon. A model is proposed in which the CoFe 2 0 4 crystallites that make up a particle consist of a core with the usual spin arrangement and a boundary surface layer with atomic moments inclined to the direction of the net magnetization. The temperature dependency of this structure is also examined.