Voltage Control of Perpendicular Exchange Bias in Multiferroic Heterostructures

Perpendicular exchange bias (EB), which combines perpendicular magnetic anisotropy and ferromagnetic (FM)–anti-ferromagnetic (AFM) exchange coupling, is extremely important in high-density AFM spintronics. However, the effective modulation of EB remains challenging, since the alternant spins at the AFM/FM interface are strongly pinned by the AFM layer. Voltage tuning of EB through magnetoelectric coupling provides a potential way to achieve rapid magnetization switching in an energy-efficient manner. Nevertheless, the interfacial strain mediation of perpendicular EB induced by E-field remains unexplored. In this work, perpendicular EB nanostructure by room-temperature fabrication process is obtained, and the voltage tunable perpendicular EB in Pt/IrMn/(Co/Pt)₂/Ta/(011) Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ multiferroic heterostructure is demonstrated. To enhance the voltage control effect on perpendicular EB, both strain-mediated magnetoelectric coupling and ionic liquid gating method are further investigated in the thinned EB system with the structure of Pt/IrMn/Co/Pt/Ta. As a result, the voltage induced lattice distortion effectively transmits to the AFM/FM interface, while the charge accumulation and ion migrations in gating method generate a relatively large hysteresis loop offset that has not been observed before at room temperature. The voltage manipulation of perpendicular EB at room temperature provides new possibilities toward novel AFM devices and memories with great energy-efficiency and ultrahigh density.