Electric-Field Induced Reversible Switching of the Magnetic Easy Axis in Co/BiFeO₃ on SrTiO₃

Electric-field (E-field) control of magnetism enabled by multiferroic materials has the potential to revolutionize the landscape of present memory devices plagued with high energy dissipation. To date, this E-field controlled multiferroic scheme has only been demonstrated at room temperature using BiFeO₃ films grown on DyScO₃, a unique and expensive substrate, which gives rise to a particular ferroelectric domain pattern in BiFeO₃. Here, we demonstrate reversible electric-field-induced switching of the magnetic state of the Co layer in Co/BiFeO₃ (BFO) (001) thin film heterostructures fabricated on (001) SrTiO₃ (STO) substrates. The angular dependence of the coercivity and the remanent magnetization of the Co layer indicates that its easy axis reversibly switches back and forth 45° between the (100) and the (110) crystallographic directions of STO as a result of alternating application of positive and negative voltage pulses between the patterned top Co electrode layer and the (001) SrRuO₃ (SRO) layer on which the ferroelectric BFO is epitaxially grown. The coercivity (H_C) of the Co layer exhibits a hysteretic behavior between two states as a function of voltage. A mechanism based on the intrinsic magnetoelectric coupling in multiferroic BFO involving projection of antiferromagnetic G-type domains is used to explain the observation. We have also measured the exact canting angle of the G-type domain in strained BFO films for the first time using neutron diffraction. These results suggest a pathway to integrating BFO-based devices on Si wafers for implementing low power consumption and nonvolatile magnetoelectronic devices.