Site-engineered ferromagnetism in Ca and Cr co-substituted Bismuth Ferrite Nanoparticles

TL;DR

This study demonstrates that co-substituting Ca and Cr into Bismuth Ferrite nanoparticles enhances their magnetic and ferroelectric properties at room temperature, with potential applications in spintronics and memory devices.

Contribution

The paper introduces novel Ca and Cr co-substituted Bismuth Ferrite nanoparticles with improved multiferroic properties, synthesized via a sol-gel method and characterized thoroughly.

Findings

Enhanced magnetic properties near 62 nm particle size.

Presence of exchange bias linked to core-shell structure.

Increased Neel temperature with Ca substitution.

Abstract

Multiferroic perovskites that exhibit room temperature magnetization and polarization have immense potential in the next generation of magneto-electric and spintronic memory devices. In this work, the magnetic and ferroelectric properties of Bismuth Ferrite, BiFeO3 (BFO) nanoparticles (NPs) were enhanced through simultaneous A and B site Ca and Cr co-substitution. Novel compositions of Bi0.97Ca0.03CrxFe1-xO3 (x=0, 0.01, 0.03, 0.05) were synthesized using the sol-gel route and annealed at 550 degrees Celcius. Rietveld Refinement of XRD patterns confirmed high phase purity, while SEM analysis revealed a decreasing trend in average particle size with increasing dopant concentration. Hysteresis loops showed enhanced magnetic properties as particle size approached the spin cycloid wavelength (around 62 nm), disrupting the intrinsic antiferromagnetic ordering of BFO. Moreover, the presence of exchange bias in the NPs was linked to the formation of core-shell structure. Temperature dependent magnetization studies showed an increase in N\'eel temperature upon Ca substitution. XPS analysis confirmed that Bi0.97Ca0.03FeO3 samples exhibited the highest oxygen vacancy concentration, while Fe3+ remained the dominant oxidation state across all compositions. Ferroelectric polarization loop measurements showed enhanced remanent polarization in doped samples, with leakage linked to oxygen vacancies and extrinsic microstructural effects.