EFFECT OF TITANIUM DOPING AND TEMPERATURE VARIATION ON STRUCTURE AND MAGNETIC STATE OF BARIUM HEXAFERRITE

Abstract A number of solid solutions based on BaFe12-xTixO19 M-type barium hexaferrite doped with titanium cations up to x = 2.00 were obtained using conventional ceramic technology. The phase composition, crystal structure and unit cell parameters were refined by the Rietveld method using powder X-ray diffraction data up to T = 900 K. It was found that all the compositions have a magnetoplumbite structure satisfactorily described by P63/mmc space group (No. 194). With increasing temperature and doping concentration, the unit cell parameters increase almost monotonically. The minimum volume of V ~ 696.72 A3 was determined for the composition with x = 1.00 at T= 100 K, while the maximum value of V ~ 714.00 A3 is observed for the composition with x = 2.00 at T= 900 K. The mechanism of occupation nonequivalent crystallographic positions with titanium cations is established. The spin-glass component of the magnetic phase state is fixed. The Tdif temperature of the difference between the ZFC-FC curves decreases with an increase in the concentration of titanium cations and the magnetic field from ~ 237.2 K to ~ 44.5 K, while the Tinf inflection temperature of the ZFC curve increases from ~ 21.0 K to ~ 23.8 K. With an increase in the doping concentration, both the Dav average and Dmax maximum clusters grow up to ~ 100 nm. As the magnetic field increases above the critical value, the spin-glass component disappears. For compositions with x \u003e 1.00, the magnetization is not saturated in fields up to 6 T. Along with the formation of the spin-glass component, doping with titanium cations for barium hexaferrite lowers the TC Curie temperature down to T ~ 600 K. The Ms spontaneous and Mr remanent magnetizations, as well as the Bc coercivity, decrease with increasing doping concentration almost monotonically, while the latter has an inflection point at x = 1.00. The minimum values of spontaneous and remanent magnetization, as well as coercivity, are observed for the composition with x = 2.00 and amount to Ms ~ 17.7 emu/g, Mr ~ 1.9 emu/g, and Bc ~ 3.9*10-3 T, respectively. An interpretation of the magnetic state of the doped BaFe12-xTixO19 barium hexaferrite is given taking into account the mechanism of occupation nonequivalent crystallographic positions with titanium cations.