Interface assisted high magnetoresistance in BiFeO3/Fe97Si3 thin film at room temperature

Abstract

Bilayer thin films of multiferroic oxide BiFeO3 and metallic alloy Fe97Si3 deposited by RF-magnetron sputtering have been investigated to understand spin polarized electron transport across bilayer interface. Effect of BiFeO3 thickness variation on magnetic and magnetotransport properties of bilayer thin films has been analyzed. An induced unidirectional magnetic anisotropy in bilayer thin films has been observed by interface coupling between antiferromagnetic BiFeO3 and ferromagnetic Fe97Si3 spin magnetic moments. Increasing interface roughness with increase in BiFeO3 film thickness has been found to be a regulatory factor for inducing in-plane unidirectional anisotropy and exchange interaction at bilayer interface. A high magnetic moment ∼315 emu/cc originated at room temperature by uncompensated interface spin density has been measured in 30 nm thick BiFeO3 film. Magnetic inhomogeneities at interface give rise to a spin glass like phase responsible for spin flip scattering at bilayer interface. Enhanced low field magnetoresistance ∼30% in 60 nm thick BiFeO3 film is ascribed to intensified scattering from disordered interface states with increasing BiFeO3 thickness. Magnetodielectric measurements (applied magnetic field 1 kOe) have revealed five times increase in relaxation time of charge carriers inside grains confirming intergrain charge transport dominated by alignment of magnetic moments of nearby grains via exchange coupling. High value of magnetoresistance ∼46% in 60 nm thick film of increased grain size is due to enhanced critical length for charge transport. Observed room temperature magnetoresistive properties of BiFeO3/Fe97Si3 thin films are critical for developing multiferroic antiferromagnetic based spintronic devices.