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We have investigated the structural, magnetic, magnetodielectric, and magnetoimpedance characteristics of Aurivillius-structured Bi5Ti3FeO15 (BTFO) synthesized by a generic solid-state reaction route. Rietveld refinement of X-ray diffraction pattern at room temperature (RT) confirms orthorhombic crystal structure (space group A21am). In BTFO, octahedral distortion of the perovskite unit occurs due to antisite defects Fe/Ti in the BO6 site, which results in the formation of Fe–O clusters. Raman spectra also reveal Ti/FeO6 octahedral distortion due to the vibration of Bi ions in the perovskite layer. Magnetic field-dependent magnetization (M–H) and electric field-dependent polarization (P–E) measurement at RT indicate the existence of multiferroic behavior in BTFO. The M–H hysteresis at 5 K suggests that the non-interacting superparamagnetic state is dominant over the local short-range antiferromagnetic (AFM) ordering. The AFM interaction arises due to the random distribution of antisite defects Fe/Ti causing the distorted Fe–O octahedral unit. These canted spin interact via the Dzyaloshinskii–Moriya (DM) interaction. The superexchange interaction between the Fe–O–Fe ions is stronger than the next-nearest-neighboring Fe–O–O–O–Fe interaction. This happens due to the intermediate fluorite-like layer (Bi2O2)2+, which opposes the long-range exchange interaction. The negative magnetodielectric (MD) effect is more prominent at low frequency (~ 100 Hz) due to the extrinsic contribution. In contrast, in the high-frequency region (> 50 kHz), the intrinsic contribution dominates, which is further ascertained by magnetoimpedance (MI) measurement. The maximum magnitude of the MD effect is found to be ~ 0.32% at a magnetic field of 13 kOe at 150 K. Lastly, the ferroelectric characteristic of the sample is obtained from the P–E measurement with a polarization value of 4.35 µC/cm2 with an applied electric field of 70 kV/cm. [ABSTRACT FROM AUTHOR]

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 ∝ 1/T) suggests that the ac conduction mechanism of KBFO follows correlated barrier hoping (CBH) model. [ABSTRACT FROM AUTHOR]