Multiferroic Properties of BiFeO<inf>3</inf>(110) Films on CoPt(111) Electrode Layer on Glass Substrates at Reduced Temperatures

Abstract

BiFeO 3 (BFO) with a perovskite structure, which possesses ferroelectric and magnetic orderings at room temperature (RT), has attracted much attention for potential applications in advanced spintronic and memory devices based on the electric-magnetic couplings. [1]–[3] In order to facilitate these coupling, the use of ferromagnetic (FM) bottom electrode to induce specific texture of BFO seems to be a most direct way. In this study, BFO films are grown on FM CoPt(111) underlayer on glass substrate by sputtering. In addition to serving as a FM bottom electrode, CoPt(111) is also expected to reduce the formation temperature of BFO phase [3]–[4]. A CoPt layer with optimized (111)-texture was used to grow high-quality BFO film. Structure, ferroelectric, and magnetic properties of BiFeO 3 (110) films grown on 10-50-nm-thick ferromagnetic CoPt(111) buffered glass substrate at 350–550°C have been studied. (110)-texture of BFO films is developed at the reduced temperature as low as 400–550°C, but isotropic orientation is found at higher temperature of 600 °C. Low temperature deposition results in dense microstructure, fine grains, and smooth surface morphology, which are favorable for applications. BFO(110) films on CoPt(111) underlayer exhibit desired ferroelectric and magnetic properties. Electrical polarization (2Pr) of 96–137 $\mu \text{C}/\text{cm}^{2}$ and coercive field $(\text{E}_{\text{c}})$ of 495–618 kV/cm for studied BFO (110) films are comparable to those grown on single crystal substrates. Moreover, exchange bias between BFO and CoPt is observed after a field cooling from 370 °C to room temperature (RT) at 2 kOe. Large exchange bias field of 155 Oe at RT and coercivity of 1631 Oe are obtained. The presented results provide useful information for the applications based on electric-magnetic interactions.