Effect of Ca Substitution on the Multiferroic Properties of BiFeO<inf>3</inf> Films on Glass Substrates at Reduced Temperature

Abstract

BiFeO 3 (BFO) perovskite compound with both ferroelectric and magnetic transition well above room temperature has attracted much attention in recent years due to promising applications in the advanced spintronic and memory devices [1]–[2]. The substitution of different valence elements for Bi in BFO provskite phase is a pronounced way to control various physical properties. Interesting structural and electrical evolutions were revealed in Bi 1 - x Ca x FeO 3 (BCFO) ceramics. [3]–[4] However, rare report on polycrystalline films of (Bi, Ca)FeO 3 is available. In this present work, BCFO films with x = 0.05, 0.1, and 0.15 are grown on fine controlled Pt(111) electrode layer on glass substrate by pulsed laser deposition. Pt layer with t = 10–30 nm in thickness was optimized to obtain strong (111)-texture and smooth surface. 200-nm-thick BCFO films were then in-situ grown at 450 °C. BCFO films exhibit typical multiferroic properties comparable to BFO films grown on single crystal substrates. Magnetization at 1 T of 5.9-8.2 emu/cm3 with coercivity of 1224–1258 Oe are obtained, which is consistent with the result of suppressed spiral spin configuration that have been revealed. Ferroelectric polarization 2P r of 124 $\mu \text{C}/\text{cm}^{2}$ and coercive field $\text{E}_{\text{c}}$ of 394 kV/cm are obtained for BCFO films with x = 0.05, and are almost linearly decreased with x to 91 $\mu \text{C}/\text{cm}^{2}$ and 294 kV/cm for x = 0.15, respectively, which might be related to reduced average displacement of A site ions relative to FeO 6 octahedral with Ca2+ substitution for Bi3+. The magnetic and electric properties, including ferroelectric and leakage behaviors are as functions of Ca content. Detailed results of microstructure analysis provide useful information concerning how the multiferroic properties are modified by Ca substitution.