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.”

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