Strong Impact of Underlayers on the Voltage‐Controlled Magnetic Anisotropy in Interface Engineered Co/MgO Junctions with Heavy Metals

The voltage-controlled magnetic anisotropy (VCMA) effect in ferromagnets is of crucial interest for next-generation non-volatile magnetic memory technologies since it enables spin manipulation with low power consumption in addition to high-speed operation and high writing endurance. Although intense efforts are made in the past decade to increase the efficiency of the purely electronic VCMA effect, the physical origin of this phenomenon is still elusive, particularly for interface-engineered ferromagnetic materials. Here, a pathway is proposed to tune the VCMA effect by exploiting a combination of the insertion of heavy metals and underlayers. Focusing on Co/MgO junction deposited on Os underlayer, a large VCMA effect of -100 fJ V-1 m(-1) is demonstrated with Pt insertion, which is approximate to 50% greater than the case deposited on Pt underlayer. On the other hand, smaller VCMA effect is observed with Ir insertion, and even a positive VCMA effect is observed with Os insertion, which are vastly different from the case deposited on Pt underlayer. The systematic variation of VCMA coefficient depending on the underlayer materials implies the effect of electron depletion from underlayers. The concepts demonstrated here can be applicable for other spintronic materials and may open a way to interfacial spin-orbit engineering for VCMA effect.