Magnetization, magnetic interactions and spin structure in ultrafine rare-earth iron garnets

Abstract

The study involves the investigation of basic magnetic properties of ultrafine rare-earth iron garnets in the size range 1.0-35 nm, prepared by a citrate precursor method. The crystallites of 10-35 nm size are monolithic ferrimagnetic particles which have saturation magnetization and magnetic interactions (as shown by the Curie temperature) comparable with those of bulk crystalline garnets. The small reduction in saturation magnetization in the 10-20 nm crystallites is attributed to spin canting and non-collinearity at the surface of the crystallites, and a model based on surface spin canting is proposed for the spin structure of these crystallites. The magnetization and magnetic interactions of smaller crystallites of 1.0-1.5 nm which exist as X-ray amorphous magnetic clusters are different from those in the bulk crystalline garnets. Reduction in the rare-earth sublattice contribution due to a weakening of the R3+-O2-Fe3+ super-exchange interaction in the disordered state accounts for the difference in saturation magnetization in these magnetic clusters, whereas the enhanced Curie temperatures are attributed to an increase in the number of effective magnetic interactions in the disordered state. A model based on bulk spin noncollinearity is proposed for the spin structure of the magnetic clusters consisting of 1.0-1.5 nm crystallites.