Switching fixed magnetic skyrmions in continuous film and patterned nanodots using Voltage Control of Magnetic Anisotropy

Abstract

Although current induced motion of magnetic skyrmions have been extensively studied in recent work [1-3], manipulation of magnetic skyrmions that are fixed in space can also be utilized to implement such devices. We have recently shown that, skyrmion core reversal and switching between ferromagnetic states via an intermediate skyrmion state can be achieved in the free layer of an MTJ using Voltage Control of Magnetic Anisotropy (VCMA) which could result in energy efficient memory devices with smaller footprint [4-5]. In this work, we demonstrate experimental evidence of voltage controlled switching of fixed skyrmions in both continuous film [6] and confined geometry. The continuous heterostructure film stack consists of IrMn/CoFeB/MgO layers. The exchange biased structure allows stabilization of skyrmions without any external magnetic field. Upon application of a voltage pulse, the perpendicular magnetic anisotropy (PMA) changes at the ferromagnet/oxide interface. When the PMA is increased by applying a negative voltage pulse, skyrmions are annihilated. On the other hand, skyrmions can be recreated using a positive voltage pulse. We will also present micromagnetic simulations which reveal the detailed magnetization dynamics of this switching. Next, we will show voltage control of skyrmions in patterned nanodots composed of Ta/CoFeB/MgO multilayers. The geometric confinement is expected to influence the switching dynamics as shown in Fig. 1 [4,5]. To systematically modulate the confinement strength, we fabricated nanodots of varying lateral dimensions. The magnetization configurations are imaged using Magnetic Force Microscopy (MFM). Preliminary result of MFM imaging of skyrmion states under 1300 mV applied voltage in a ~5 µm dot is shown in Fig. 2. We will present detailed analysis of the confinement effect on skyrmion switching using further in-situ MFM imaging and rigorous micromagnetic simulations and compare these observations with the switching in thin films. Acknowledgement: NSF CCF collaborative grants: 1909030 and 1909416.