Impact of strontium substitution on the structural, magnetic, dielectric and ferroelectric properties of Ba_1-xSr_xFe₁₁Cr₁O₁₉(x = 0.0–0.8) hexaferrites

Strontium substituted barium hexaferrites i.e., Ba_1-xSr_xFe₁₁Cr₁O₁₉ with x = 0.0–0.8 were prepared via co-precipitation technique. Single-phase magnetoplumbite structure was confirmed for all samples by X-ray diffraction, whereas scanning electron microscopy showed the variation in microstructure on Sr²⁺ substitution. Magnetic measurements revealed that the substitution causes prominent enhancement in saturation magnetization and coercive field for x = 0.4 sample. However, under same condition, decrease in real part of dielectric permittivity, dielectric loss tangent and ac conductivity were observed by impedance spectroscopy, while these parameters started to increase for x > 0.4. The dielectric permittivity exhibited frequency-dependent dispersive behavior due to Maxwell-Wagner interfacial polarization whereas weak ferroelectric hysteresis loops were obtained for the prepared samples. Moreover, it was found that the Sr²⁺ substitution substantially enhanced the resistive properties which is elucidated in term of localization of charge carrier's mobility due to reduction in Fe³⁺-O-Fe²⁺ network and microstructural variations. Here, it is proposed that x = 0.4 sample exhibits maximum magnetization (64 emu/g), moderate real part of dielectric permittivity at low frequency (>10³), diminished dielectric loss tangent (~0.05) and colossal value of resistance (~10¹⁰ Ω) which makes this material interesting for high frequency applications.