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 <i>E</i>-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

Spatially Resolved Ferroelectric Domain-Switching-Controlled Magnetism in Co₄₀Fe₄₀B₂₀/Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ Multiferroic Heterostructure

Intrinsic spatial inhomogeneity or phase separation in cuprates, manganites, etc., related to electronic and/or magnetic properties, has attracted much attention due to its significance in fundamental physics and applications. Here we use scanning Kerr microscopy and scanning electron microscopy with polarization analysis with in situ electric fields to reveal the existence of intrinsic spatial inhomogeneity of the magnetic response to an electric field on a mesoscale with the coexistence of looplike (nonvolatile) and butterfly-like (volatile) behaviors in Co₄₀Fe₄₀B₂₀/Pb­(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ ferromagnetic/ferroelectric (FM/FE) multiferroic heterostructures. Both the experimental results and micromagnetic simulations suggest that these two behaviors come from the 109° and the 71°/180° FE domain switching, respectively, which have a spatial distribution. This FE domain-switching-controlled magnetism is significant for understanding the nature of FM/FE coupling on the mesoscale and provides a path for designing magnetoelectric devices through domain engineering