Temperature-dependent magnetodielectric, magnetoimpedance, and magnetic field controlled dielectric relaxation response in KBiFe2O5

Abstract

In this work, polycrystalline KBiFe2O5 (KBFO), belonging to the brownmillerite class of monoclinic structure with space group P2/c, is synthesized using a solid-state reaction route. Magnetodielectric (MD) and magnetoimpedance (MI) characteristics of KBFO are studied over a wide temperature (10–300 K), magnetic field (0–1.3 T), and frequency (100 Hz to 1 MHz) range. Zero-field-cool (ZFC) and field-cool (FC) magnetization data show a bifurcation around 11 K, indicating blocking temperature (TB). At room temperature, MD and MI data as a function of the magnetic field shows maximum MD and MI coupling to be ∼−0.6% and ∼0.7%, respectively, at 50 kHz. With the decrease in temperature from 300 K to 50 K, magnetodielectric strength decreases (−0.6% to −0.06%), whereas magnetization increases from canted-antiferromagnetic (MS ≈ 0.16 emu g−1) to a weak ferromagnetic state (MS ≈ 0.44 emu g−1). It indicates the existence of Inverse Dzyaloshinskii-Moriya interaction causing MD coupling in KBFO. MD behavior is also reflected in magnetic field-dependent dielectric relaxation phenomena demonstrated through magnetic field-dependent activation energies. The difference in activation energies of magnetic field-dependent conduction mechanism (Eg ≈ 0.370 ± 0.018 eV) and MD loss relaxation (Eg ≈ 0.183 ± 0.006 eV) indicate both have a different origin. The presence of the capacitive MI effect demonstrates that the observed magnetodielectric coupling is intrinsic. The existence of both temperatures-dependent MD and MI coupling in KBFO makes it suitable for dynamic random access memory as well as novel magnetic sensors.