  Electric-field (E-field) control of magnetism enabled by multiferroics has
the potential to revolutionize the landscape of present memory devices plagued
with high energy dissipation. To date, this E-field controlled multiferroic
scheme at room temperature has only been demonstrated using BiFeO3 (BFO) films
grown on DyScO3 (refs 1 and 2), a unique and expensive substrate, which gives
rise to a particular ferroelectric domain pattern in BFO. Here, we demonstrate
reversible E-field-induced switching of the magnetic state of the Co layer in
Co/BFO (001) thin film heterostructures fabricated on SrTiO3 substrates. The
angular dependence of the coercivity and the remanent magnetization of the Co
layer indicates that its easy axis reversibly switches by 45{\deg} back and
forth between the (100) and the (110) crystallographic directions of SrTiO3 as
a result of alternating application of positive and negative voltage pulses on
BFO. The coercivity of the Co layer exhibits a hysteretic behavior between two
states as a function of voltage. To explain the observation, we have also
measured the exact canting angle of the antiferromagnetic G-type domain in 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 non-volatile magnetoelectronic devices.
