Bi2O3 adjusting equivalent permeability and permittivity of M-type barium ferrite for antenna substrate application

In this paper, Co-Ti doped M-type barium ferrite [Ba(CoTi)1.22Fe9.56O19] was prepared at low temperature (925 °C) in O2 atmosphere with different amounts of Bi2O3 sintering additive (x = 5–14 wt%). XRD showed superfluous Bi2O3 additive led to BiFeO3 phase formation, which is the important factor to adjust properties of material. SEM revealed that the grain size diminished gradually. For magnetic and dielectric properties, with different amounts of Bi2O3, saturation magnetization (Ms) decreased and coercivity (Hc) gradually increased. Complex magnetic permeability and dielectric permittivity presented excellent regularity, and the equivalent permeability and permittivity were obtained when x = 5 wt%. At x = 5 wt%, the real part of permeability (μ′) and permittivity (ε′) were about 18.3 at a range of 10 MHz–1.0 GHz, the magnetic loss (tan δμ) was about 3.4 × 10−2, and the dielectric loss (tan δε) was about 2.8 × 10−3. It showed that Bi2O3 not only lowered the sintering temperature of ferrite, but also adjusted the magnetic and dielectric properties, and the material has potential to apply for miniaturizing efficient antennas at high frequency.