Microwave ferrites, part 1: fundamental properties

Abstract

Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1-100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe 12 O 19 and SrFe 12 O 19 , which have high effective internal magnetic anisotropy that also contributes to the permanent bias.Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent i

Optimum preparation conditions of Fe-deficient Ca-based M-type ferrite

“…The Curie temperatures of BaFe12O19 and SrFe12O19 are 450°C and 460°C, respectively. 1)- 4) The unit cell of M-type ferrite is composed of two kinds of block units, where a R-block and a S-block are stacked up alternately (RSR * S * ). The symbol * means 180° rotation of the corresponding block around the c-axis.…”

Magnetic study of M-type doped barium hexaferrite nanocrystalline particles

“…M-type barium hexaferrites (BaFe 12 O 19 ) with magnetoplumbite structure have been intensively investigated in the past years as a material for permanent magnets, high-density recording, future multiferroic and high frequency applications [1,2,3,4]. In general, these materials have large saturation magnetization, high coercivity, high Curie temperature, large uniaxial magnetic anisotropy and good chemical stability [5,6,7,8].…”

Optimum Conditions for Synthesizing Fe Substituted Hibonite

“…[1][2][3] In spite that pure M-type CaFe12O19 phase does not exist in the CaO-Fe2O3 diagram, [4][5][6] the M-type phase becomes stable with the addition of a rare-earth element of lanthanum to CaFe12O19. 7,8) The optimum synthesis condition of the (Ca,La)-based M-type ferrite with the highest magnetization was recently clarified.…”