Estudo das propriedades dielétricas e magnéticas da hexaferrita tipo M (BaxSr1-xFe12O19) para uso em dispositivos eletrônicos

Abstract

The ferrites are magnetic ceramic materials widely used in the manufacturing of magnetic devices due to the high resistivity at high frequencies, flexibility in adjusting the magnetic properties, easy preparation and low price. The substitution of Fe 3+ for Ba 2+ ions is an effective method to modify the magnetic properties of barium hexaferrite. The aim of this study was to synthesize the M-type hexaferrite (BaXSr1_ XFe12O19) and study their structural, dielectric and magnetic properties by the replacing of Ba +2 for Sr +2 ions and to verify their applications as magneto-electronics devices in the radio frequency (RF) and microwave (MW) range. To obtain the alloy in the required stoichiometry a high-energy milling ball and the appropriate parameters of time and temperature (calcination at 1000 °C/24 h) were used. To structural characterization of alloys obtained, x-rays diffraction, infrared and Mbssbauer spectroscopy analysis were realized. Aiming at the technological application of hexaferrite BaXSr1_XFe12O19 a study of the electrical and magnetic behavior in the RF and MW range was realized. The results showed that the substitution of Ba 2+ for Sr 2+ ions in the structure of barium hexaferrite, changed its dielectric and magnetic properties. The dielectric permittivity (Er") in the range of RF decreases sharply while in MW range this decrease was less intense. The dielectric properties of the samples were influenced by the grains and grain boundaries, because it showed two relaxation processes, which may be related to the electrical conductivity of the samples. The results obtained in the hysteresis curve suggest that the samples became a harder magnetic material (increase of coercive field - HO when the Ba ion concentration decreases in the alloy, which may be applied on devices in the MW range; the grain sizes varied non-linearly, and the barium ion had a greater influence in the hexaferrite alloys. The studies of the antenna resonator (ARHS) of hexaferrite showed good performance, because the temperature coefficients (TO were very promising and can be applied in MW devices, since that are relatively simple and easy to manufacture. The bandwidth (BW) results of the alloys showed that these can be used as antennas which operate in broadband, since this device is desirable for various applications in communications, due to the rapid growth of services such as videoconferencing, communications via satellite and wireless etc.