Influence of BiFeO3 phase on perpendicular magnetic anisotropy in Co/Pt

Abstract

Using LaAlO3 (100) substrates and a 17-nm thick Ca0.96Ce0.04MnO3 (CCMO) buffer layer, we grew BiFeO3 (BFO) thin films with various thicknesses (18nm, 23nm, and 44nm) via pulsed laser deposition (PLD). X-Ray diffraction (XRD), Reciprocal Space Mapping (RSM) and Atomic Force Microscopy (AFM) techniques are employed to characterize the thickness, structure and surface morphology of the films. The large misfit of lattice constants between BFO films and LAO substrates exerts a large compressive strain on the BFO film, which initially stabilizes BFO in the tetragonal (T-) phase. A mixture of T-phase and rhombohedral (R-) phase emerges when the BFO thickness exceeds 20nm. As the BFO film thickness increases, the proportion of R-phase BFO increases as verified by AFM and XRD. Using DC magnetron sputtering, magnetic multilayers of Pt(4nm)/Co(0.8nm)/Pt(1.5nm) were deposited on top of these BFO films. Both Anomalous Hall Effect (AHE) and SQUID-VSM measurements reveal that the mixed-phase BFO favours a perpendicular magnetic anisotropy (PMA) of the upper Pt/Co/Pt multilayers, while the pure T-phase BFO film with smaller thickness suppresses the PMA (Fig.1 and Fig.2). Considering the R-phase BFO at the surface of the mixed-phase BFO film can change reversibly to T-phase BFO when applying electric field across BFO, this finding may provide a new route for realizing the electrical control of PMA in hybrid ferromagnetic-multiferroic structures. **