Fig. 1
Experimental setup, monodomain BiFeO3 and FE–AF–FM correlations. a Schematic diagram of in situ ferroelectric switching during PEEM imaging to study exchange coupling between monodomain BiFeO3 and Co films. The magnetoelectric heterostructure is shown as mounted in the PEEM, with incoming circular and linear polarized light used for XMCD and XMLD measurements, respectively. The photon energy is tuned to the Co L 3 edge for the XMCD measurement and Fe L 3 edge for the XMLD measurement so that the ferromagnetic Co and antiferromagnetic BiFeO3 layers can be selectively probed. The ferroelectric state of the BiFeO3 can be switched in situ by 71° from the down state to the up state, allowing the properties of the ferromagnetic Co and surface antiferromagnetic BiFeO3 layers to be characterized in the down and up states. Modeling of the surface antiferromagnetic spin-structure, whose results are shown in b, c (“BiFeO3 (surface)”), is performed via polarization angle scans varying the linear polarization angle (θ E) at different sample azimuths (ϕ M). The antiferromagnetic state in the bulk of the BiFeO3 film is additionally probed ex situ ND in both r 1 – and r 3 + states, also shown in b and c, respectively (“BiFeO3 (bulk)”); a non-bulk-like spin-cycloid configuration of BiFeO3 is observed in both down and up states. The surface AF order in the down state is cycloidal and identical to the cycloid seen by ND, while in the up state, a component of collinear AF order appears only at the surface with its axis in a vertical plane that includes the miscut direction. Correlated with the changes in surface antiferromagnetic order in BiFeO3, the ferromagnetic moments of Co lie along the substrate steps in the down state and rotate ~ 90° toward the miscut direction in the up state. PEEM measurements were taken ~ 120 K. The BiFeO3 (bulk) refers to properties averaged over the entire film thickness, for which contributions from near the interfaces are negligible
