Advances in Engineering and Applications of Hexagonal Ferrites in Russia

Abstract

Richard Feynman (Feynman, 2005) once stated that ferrites were one of the most difficult areas for theoretical description, but the most interesting for studies and practical applications. These words are especially true when dealing with a special type of ferrites, which have a hexagonal crystallographic structure – hexagonal ferrites, or hexaferrites. The world‘s first permanent magnets based on ferroxdure hexagonal barium ferrite BaFe12O19 (equivalent to BaO·6(Fe2O3), also called BaM) appeared in 1951 (Rathenau et al., 1952). The main engineering problem that was solved at that time was the replacement of cumbersome metallic (Niand Co-alloy) magnets by comparatively compact and lightweight permanent magnetic systems. The systematic study and applications of gyromagnetic properties of hexaferrites started in 1955 (Weiss & Anderson, 1995; Weiss, 1955; Sixtus et al., 1956). Currently, in the world, enormous progress in fundamental theoretical and experimental laboratory studies of various properties of hexaferrites, their synthesis, and engineering of a wide range of microwave and mm-wave coatings and devices on their basis has been achieved – see, for example, papers (Harris et al., 2006, 2009) and references therein. Hexaferrites as the materials for extermely high-frequency (EHF) range, Ka (27-40 GHz), U (40-60 GHz), V (60-80 GHz), W (80-100 GHz) bands, and higher, have been also studied and applied in Russia since middle 1950s. Authors of this paper, being apprentices and followers of the outstanding Russian scientists, V.A. Kotelnikov, L.K. Mikhailovsky, and K.M. Polivanov. V.A. Kotelnikov named the millimeter waveband “a nut in a hard shell”, deeply believe that the practical development of this waveband is possible only when using hexaferrites. Herein, the summary of achievements in engineering hexagonal ferrites and various devices of on their basis in Russia for the past over 50 years is presented. In 1955-1956, a then young scientist from Radio Engineering Department of Moscow Power Engineering Institute, L.K. Mikhailovsky, studied microwave ferrites and developed devices operating at the ferrimagnetic resonance (FMR) with new functional possibilities, such as a magnetic detector and a gyromagnetic cross-multiplier. For mm-wave applications, Mikhailovsky proposed to use instead of huge bias magnets just the internal field of