Anisotropic exchange coupling interaction between hard-hard magnetic grains in sintered SrFe12O19 ferrites

Exchange coupling interaction in sintered magnetic materials is generally isotropic. In this study, the anisotropic exchange coupling interaction was found in sintered oblate cylindrical SrFe12O19 (SrM) specimens obtained by the SrM nanopowders synthesized via a hydrothermal method. According to Henkel plots, the exchange coupling interaction between hard-hard magnetic grains was found in both as-pressed and sintered specimens. However, the exchange coupling interaction can only be found in the in-plane direction but not in the out-of-plane direction for the sintered specimens. By building a model of a grain configuration, this anisotropy of the exchange coupling interaction was ascribed to the vertically arranged plate-like SrM grains with micrometers in width but nanometers in thickness, which was confirmed by morphologies of cross sections in fractured specimens.