Effect of titanium substitution and temperature variation on structure and magnetic state of barium hexaferrites

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 P6(3)/mmc space group (No. 194). With increasing temperature and doping concentration, the unit cell parameters increase almost monotonically. The minimum volume of V similar to 696.72 angstrom(3) was determined for the composition with x = 1.00 at T = 100 K, while the maximum value of V similar to 714.00 angstrom(3) 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 T-dif temperature of the difference between the ZFC-FC curves decreases with an increase in the concentration of titanium cations and the magnetic field from similar to 237.2 K to similar to 44.5 K, while the T-inf inflection temperature of the ZFC curve increases from similar to 21.0 K to similar to 23.8 K. With an increase in the doping concentration, both the D-av average and D-max maximum clusters grow up to similar to 100 nm. As the magnetic field increases above the critical value, the spin-glass component disappears. For compositions with x > 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 T-C Curie temperature down to T similar to 600 K. The M-s spontaneous and M-r remanent magnetizations, as well as the B-c 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 M-s similar to 17.7 emu/g, M-r similar to 1.9 emu/g, and B-c similar to 3.9 x 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. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

A series of solid solutions based on BaFe12-xTixO19 M-type barium hexaferrite doped with titanium cations have been obtained, and the unit cell parameters increase monotonically with temperature and doping concentration, while the spin-glass component in the magnetic phase state is fixed.