Extended Data Figure 7: Magnetic hysteresis curves from BiFeO₃/Co_0.9Fe_0.1 (2.5 nm) and BiFeO₃/SrTiO₃ (1 nm)/Co_0.9Fe_0.1 (2.5 nm) heterostructures.

a, Schematic of the BiFeO₃/Co_0.9Fe_0.1 heterostructure with the directions of the net in-plane polarization (P_net IP, the vector sum of the (001)_p surface projections of the two polarization variants) and a 200 Oe magnetic field (H_growth) applied during the deposition of the Co_0.9Fe_0.1. The growth field was used to test the strength of the coupling to BiFeO₃, given that the growth field should attempt to induce a uniaxial anisotropy in that direction. Magnetic hysteresis loops taken along different in-plane angles rotating from the direction of the growth field show that despite the growth field the easy axis is found to parallel the axis set by P_net IP. b, Schematic of an experimental configuration similar to that in a; however, a 1-nm-thick layer of insulating and non-magnetic SrTiO₃ has been deposited onto the BiFeO₃ before the deposition of Co_0.9Fe_0.1. The magnetic loops from the BiFeO₃/SrTiO₃/Co_0.9Fe_0.1 heterostructure are plotted in blue and have a uniaxial anisotropy in the direction of the growth field (orthogonal to the axis set by P_net IP) with reduced strength (lower saturation and switching fields) compared to those obtained from the BiFeO₃/Co_0.9Fe_0.1 heterostructure in a (red curves).