Hexagonal ferrite: from macro- to nanocrystal

Abstract

The directions and most important results of studies of the fundamental magnetic properties of hexagonal ferrites performed at Kharkov National University over the last 50 years are reviewed. The influence of the basic factors (size, surface, and collective) specific to small particles and ensembles of small particles on the evolution of the magnetic properties under a transition from a macro- to a nanocrystal is analyzed in a section devoted to the topical subjects “Nanophysics and nanotechnology of barium ferrite.”

Synthesis and properties of ferrite nanopowders for epoxy‐barium hexaferrite‐nanocarbon composites for microwave applications

“…An object of peculiar interest from both theoretical and practical points of view is the magnetic nanocrystal, since the presence of additional degree of freedom (magnetic moment) allows one to control the magnetic state by varying the size of the particles . The main regularities in the change of physical properties of ultrasmall magnetic particles are associated with so called finite size effects: the impact of surface as a structural defect and the proximity of particle volume value to a critical value . In this case a significant influence of thermal fluctuations of magnetic moment of particles is associated with a transition from magnetostable to superparamagnetic state eventually .…”

“…The main regularities in the change of physical properties of ultrasmall magnetic particles are associated with so called finite size effects: the impact of surface as a structural defect and the proximity of particle volume value to a critical value . In this case a significant influence of thermal fluctuations of magnetic moment of particles is associated with a transition from magnetostable to superparamagnetic state eventually . The formation of the nano‐sized barium hexaferrite particles greatly depends on the method of synthesis, so the problem of obtaining hexaferrite particles of critically small size (close to a single‐domain limit) with the minimal amounts of different oxide phases is of great interest today .…”