| With the advent of the era of big data,large amounts of data is putting forward higher request for information storage devices and also makes the current information storage technology facing many severe challenges.Therefore,storing information in a more efficient way is particularly important.Compared to the traditional semiconductor random access memory,magnetic random access memory?MRAM?is expected to become the candidate of the next-generation information storage due to the non-volatile,higher density,lower power consumption,better stability,strong radiation resistance and so on.Among MRAMs,the most developing potential one is the spin-orbit torque?SOT?based magnetic random access memory?SOT-MRAM?.The spin Hall effect or/and Rashba effect resulted from heavy metals?HMs?with strong spin-orbit coupling are considered to be the major sources that can enable pure spin current generation or spin accumulation when passing an in-plane charge current in HMs.Therefore,the polarized spins can exert efficient torques on the adjacent ferromagnetic?FM?layer to manipulate the magnetization switching in a commonly studied HM/FM structures with perpendicular magnetic anisotropy?PMA?.At present,the studies based on SOT are mainly concentrated on manipulating magnetization switching,driving a chiral domain wall motion,exciting high-frequency spin Hall nano-oscillators and driving magnetic skyrmions,etc.Among them,the most important research is to drive the magnetization switching and chiral magnetic domain wall motion in the more efficient and fast way.In this thesis,we mainly study the current-induced magnetization switching and magnetic domain wall motion in perpendicularly magnetized heterostructures.It includes three parts as follows:Firstly,we focus our study on the physical mechanism and the role of Joule heating during current-induced magnetization switching in perpendicularly magnetized heterostructures.The obtained critical switching current density?Jc?for Pt/Co/SmOx and Pt/Co/AlOx structures with similar values of spin Hall angle(?SH)and different PMAs remains roughly constant,revealing that the coherent switching model cannot fully explain the current-induced magnetization switching.In contrast,by observing the domain wall nucleation and expansion using Kerr microscope and quantificationally comparing the effective field(?HDL)corresponding to damping-like torque,switching field(Hsw)and anisotropic field?Hk?,we conclude that the current-induced magnetization switching is dominated by the depinning model and Jc also relies on Hsw?i.e.depinning field?.In addition,the Joule heating generated from direct current plays an assisted role in the switching process by reducing Hsww and enhancing SOT efficiency.Secondly,in perpendicularly magnetized Pt/Co/Ta heterostructures,the effective SOT can be enhanced by using the Pt and Ta which show opposite signs of?SH,and the relatively low Jc about2.82×106 A/cm2 can be obtained.Furthermore,we also prepared Pt/Co/C/Ta heterostructures with PMA through interfacial graphite?C?decoration between Co and Ta and studied the variations of the Hk,Hsw,saturated magnetization?Ms?,SOTs,and Jc after C decoration as well as the effect of the temperature?T?on them.The results show that the Hk and?HDLL can be reduced,however,Jc changes a little,revealing that although?HDLL is reduced as a driving force,the reduced Hk increases the thermal disturbance of the magnetization.Therefore,the lower Jc about 3.39×106A/cm2 can be still obtained.Moreover,Jc gradually decreases as T increases,which also reveals the assisted role of T in the magnetization switching.These findings could provide a new perspective towards improving the switching efficiency and understanding the parameters related to magnetization switching and their influence factors in SOT-based spintronic devices.At last,the current-induced domain wall?DW?motion?CIDWM?and tilting in perpendicularly magnetized Pt/Co/Ta and Pt/Co/C/Ta structures are investigated via a magneto-optical Kerr microscope.The results indicate that the Dzyaloshinskii-Moriya interaction?DMI?mainly comes from the contribution of the Pt/Co interface in Pt/Co/Ta and Pt/Co/C/Ta stacks.Besides,in CIDWM,a larger DW velocity?103 larger?is observed compared to that in field-induced DW motion?FIDWM?with the same magnitude between the current generated effective field and applied magnetic field.It reveals that the current generated Joule heating also affects the DW motion.More importantly,current-induced DW tilting phenomenon is observed in Pt/Co/Ta and Pt/Co/C/Ta stacks,while this phenomenon is absent in FIDWM,demonstrating that the current generated Oersted field may play an essential role in DW tilting.These findings could provide some new designing prospects to drive DW motion in SOT-based racetrack memories. |
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