Estudo da influência de íons titânio e cobalto nas propriedades magnéticas e absorvedoras de ondas eletromagnéticas de hexaferrita de bário
Resumen
In this work Cobalt and Titanium doped Barium hexaferrites were
synthesized by the ceramic method in order to study their use as
electromagnetic absorbing materials in high frequencies. The dopants were
used individually (Ti and Co) and with both simultaneously (CT). Ceramic
characteristics and magnetic properties of calcined powders, as well as of their
pellets sintered in electric and microwave furnaces were evaluated. For the high
frequency permeability measurements, hexaferrites ring-shaped sintered and
ring-shaped composites with the hexaferrite powders and epoxi resin were
produced. Barium hexaferrite powder (BaM) presented 3.45 kOe of coercivity
and the same synthesizing conditions were used in all hexaferrites with dopant
atomic fractions of 0,2; 0,4; 0,6; 0,8; and 1,0. In Ti hexaferrites (BaFe12-xTixO19)
microstructures there were BaFe2O4, Fe2O3 and Ba3Fe10TiO20 phases and they
presented coercivities between 1,53 and 1,04 kOe. Co hexaferrites (BaFe12-
xCoxO19) microstructures showed W, Y and Z hexaferrites types phases, with
coercivities between 0,70 and 0,21 kOe. In CT hexaferrites (BaFe12-2xCoxTixO19)
it was presented CoFe2O4 phase, with coercivities between 0,09 and 1,06 kOe
was presented. Most of the pellets sintered in microwave furnace had apparent
densities close to those of the pellets sintered in electric furnace and their
coercivities were higher or equal. The grains heterogeneity increased with
dopant quantities and the Ti microstructures presented more quantity of M type
hexaferrites in comparison to other samples. The ring-shaped sintered samples
of BaM, Ti and CT hexaferrites showed ferrimagnetic ressonance peaks in 110
MHz and 780 GHz. In Co hexaferrites the presence of hexaferrites different
from M type contributed to the different tangent loss in comparison to other
hexaferrites. The tangent loss of composites showed the same peaks observed
in the ring-shaped sintered samples but with smaller intensities. These
composites showed absorption loss up to 20 dB in 12 GHz too.