Evidence of room-temperature magnetodielectric effect in brownmillerite KBiFe2O5 through magnetic, complex dielectric, and impedance study

Abstract

We have investigated the structural, magnetic, dielectric, and magnetodielectric properties of brownmillerite-structured polycrystalline KBiFe2O5 (KBFO) sample synthesized using conventional solid-state reaction route. Monoclinic structure with P2/c space group is determined from Rietveld refined X-ray diffraction (XRD) analysis. Temperatures-dependent magnetic and dielectric data show a broad hump around 510 °C, indicating the existence of magnetodielectric effect in KBFO. Room-temperature M–H hysteresis measurement possesses a weak ferromagnetic order (MR = 0.006 emu/g and Hc = 1100 Oe) originating from the canted Fe3+ moments due to antiferromagnetic ordering. This canted Fe3+ moment is also reflected in magnetic field variation of magnetodielectric (MD) measurement at room temperature, in which MD does not trace the original path by reversing the field. The highest magnetodielectric response is obtained to be ~ − 1.8% at room temperature. Modulus and complex impedance spectrum analysis attributes the bulk contribution to the observed room-temperature magnetodielectric at high frequency (> 10 kHz) and extrinsic contribution (< 10 kHz) at low frequency. The presence of temperature-dependent and non-Debye (β < 1) type of relaxation in prepared sample is confirmed from the extracted grain (Rg) and grain boundary (Rgb) contribution at different temperature. The frequency-dependent ac conductivity at different temperature follows Jonscher’s power law. The extracted power exponent “n” is decreased with increase in temperature. This behavior (n $$\propto$$ 1/T) suggests that the ac conduction mechanism of KBFO follows correlated barrier hoping (CBH) model.