Spin‐Orbit Torque Driven Magnetization Switching and Precession by Manipulating Thickness of CoFeB/W Heterostructures

Abstract

has been proposed to facilitate the electrical manipulation of magnetization switching for magnetic random access memory and magnetic logic devices by using these toques. [2][3][4][5][6] Moreover, an oscillation and precessional motion by SOT can be a candidate for various types of oscillators. [7][8][9] The spin Hall effect (SHE) and the Rashba-Edelstein interaction are expected to be the main mechanisms of the current-induced SOT, where the two main constituents are the damping-like torque and field-like torque. [10][11][12][13] In the SHE, a spin current is generated in a direction perpendicular to the applied longitudinal charge current flowing in a normal metal (NM) and accumulates spins between FM and NM layers, which exerts a damping-like torque to the magnetization in FM. [14,15] In the Rashba-Edelstein effect, which is caused by the broken space inversion symmetry at the interface, spin accumulation is generated in a direction transverse to the charge current direction in the film plane, which exerts a torque on the magnetization in a ferromagnet (FM). [16][17][18][19][20] In addition to the spin Hall and Rashba-Edelstein effects, the Oersted field generated by the current in a metallic film is an additional source of driving torque. [21,22] In a perpendicular magnetic anisotropy (PMA) structure, these torques generated from a nano-second electric pulse switch the magnetization by a domain wall motion. [23][24][25] It is known that the in-plane magnetic tunnel junction (MTJ) device by a spin transfer torque does not need an external field but takes a relatively long time for the switch due to an incubation time. [26,27] But, recently, researchers demonstrated an in-plane MTJ device by SOT showing a fast deterministic switching at a low current density. [28][29][30][31][32] This in-plane device offers various possibilities in application so that more intensive study is needed.In this work, we investigated the new aspect of in-plane SOT device depending on the amplitudes of damping-like torque, field-like torque, the Oersted field torque and demagnetization torque by a macro spin simulation. We found that the switching, oscillation, and precession could occur in the same heterostructure like W/CoFeB by using the change of the torque ratio with different NM and FM thicknesses. In addition, we constructed the dynamic map as a function of the efficiency of each torque. The expansion and the shrinkage of the switching region are reflected in the map depending on the current density.The switching of magnetization via spin-orbit torque has attracted much attention because of its fast switching and low power consumption. Numerous studies have focused on increasing the conversion efficiency from charge to spin current and out-of-plane magnetization cases. Recently, there have been reports on the fast and deterministic switching of in-plane magnetization devices. It is reported that an in-plane spin-orbit torque (SOT) device can archive the oscillation, precession, and direct switching by a combination of torques-c...

Spin–orbit torques in normal metal/Nb/ferromagnet heterostructures

“…The efficiency obtained in our SOT measurements ( ) differed from those in a spin-pumping measurement with the Nb/Ni 80 Fe 20 heterostructure ( ) 39 and in the spin absorption measurement in the lateral spin-valve structure involving the Ni 80 Fe 20 /Cu/Nb junction ( ) 40 . Although the efficiency of the charge-to-spin conversion in this study was higher than that obtained in previous studies employing other measurement methods and material combinations, it was evident that the magnitude of SOT was still low compared to that of other 5d heavy metals such as Pt (~ 0.09) 20 – 23 , Ta (~ − 0.12) 2 , 15 , 16 , 19 , and β–W (~ − 0.33) 18 , 19 , 41 . We also conducted the current-induced SOT switching measurements using the samples with PMA to verify that the relatively low efficiency is sufficient to switch the FM layer effectively.…”

Optical Verification of Physically Unclonable Function Devices Based on Spin‐Orbit Torque Switching

“…In its metastable β‐W phase, the W exhibits the largest charge‐to‐spin conversion efficiency among the transition metals. [ 17 ] It is also being widely used in the current semiconductor industry because it is semiconductor manufacturing friendly. We confirm that the W in our device is in its β‐W phase.…”

Numerical Analysis of Deterministic Switching of a Perpendicularly Magnetized Spin-Orbit Torque Memory Cell

“…H eff includes the exchange field, uniaxial perpendicular anisotropy field, demagnetization field, currentinduced field, and random thermal field at 300 K. In (1) only the damping-like torque (DLT) is considered. It has been shown that a large field-like torque (FLT) can be generated depending on the heavy metal thickness and contribute to symmetry breaking for deterministic SOT switching, affecting the switching characteristics and dynamics [13], [14], [15]. However, the magnitude and direction of the FLT/DLT ratio is still not entirely clear [16].…”