Study of magneto capacitance effect, exchange bias, XMCD and XAS in La0.8Bi0.2Fe0.7Mn0.3O3/LaNiO3/LaAlO3 multiferroic thin film

Abstract

Magneto capacitance (MC) property of La0.8Bi0.2Fe0.7Mn0.3O3/LaNiO3/LaAlO3 thin film has been studied at an applied magnetic field of 0 T and 5 T. Variation of capacitance versus frequency at different temperatures (80 K, 100 K,180 K and 200 K) with the application of magnetic field depicts the unification of ferroic (ferroelectric and ferromagnetic) properties. This is a significant aspect for a system to be multiferroic, a choice for better device application. Exchange bias effect is observed on meticulous study of hysteresis loop taken at 5 K and 10 K upto ~1 Tesla (while cooling thin film in 5 kOe of applied magnetic field) in the form of systematic shift in loops on positive side of applied magnetic field. Hysteresis loop shifts accordingly on negative side on changing the polarity of field (−5 kOe) in field cooled mode, confirming the intrinsic nature of exchange bias effect in thin film. The NEXAFS technique has been used in finding the electronic structure, charge state and local symmetry of ions present in thin film; therefore the mechanism(s) responsible for its major properties. Magnetic character of thin film is studied using x-ray magnetic circular dichroism (XMCD) measurements. NEXAFS data of Mn L3,2- edge spectra indicates the presence of Mn2+ /Mn3+ valence states with contribution from Mn4+ ions in the system, which corroborates the ferrimagnetic nature revealed by thin film. L3,2- edge of Fe along with reference compound (Fe2O3) reveals that these ions are present in trivalent state (Fe3+) in octahedral symmetry. O K-edge features compliment the magneto-electric (ME) properties of the thin film. Charge transfer multiplet calculations confirm that Mn ions exist in different charge states (Mn2+,3,+4+) whereas Fe ions exhibit single (Fe3+) valent state in thin film.