Perpendicular magnetization reversal in Pt/[Co/Ni]3/Al multilayers via the spin Hall effect of Pt

Abstract

We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]3/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 0.3 TA/m 2 . In these experiments we demonstrate a full control of each stage: i)the Ørsted field controls the domain nucleation and ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and Néel like due to the interfacial Dzyaloshinskii-Moriya interaction.Controlling the magnetization reversal using the spin transfer torque (STT) is a key ingredient for the implementation of several technologies, including for example MRAM, benefiting from the scalability of the effect [1]. However, in materials stacks using conventional STT, the magnetization reversal requires a high current density of the order of 10 10 A/m 2 , which should ideally be as small as possible in order to avoid detrimental aftereffects when flowing across tunnel junctions based-MRAM [2]. An alternative route for magnetization control is by means of the so-called spin-orbit torque (SOT), which uses materials with a strong spin-orbit coupling (SOC) such as Pt, to generate spin currents along the perpendicular directions to the charge current via its spin Hall effect (SHE). It is then possible to take advantage of this spin current with the only difference that now both charge and spin currents are orthogonal to each other in a typical multilayer system. Charge current is flowing along the interface while spin current is diffusing perpendicularly to the interface of the constitutive layers.In this vein, several experiments have been designed to demonstrate the possibility of reversing the magnetization in single ferromagnetic layer or to propagate domain walls (DWs) using materials with strong SHE [3][4][5][6][7][8].Unfortunately the exact origin of the process as well as its microscopic understanding were still far from being fully understood at the present stage [9][10][11][12][13]. Since the pioneering work from Miron et al., [3] several reports have shown some possible routes or scenarios to explain either magnetization reversal [4,[14][15][16][17][18][19][20][21] or DW propagation [5][6][7][8][22][23][24][25][26][27][28]. The latest involve DW propagation taking into account the Dzyaloshinski-Moriya interaction (DMI) at non magnetic/magnetic interfaces in magnetic multidomain configurations [7-9, 15-19, 21-26]. One common point of these studies is the use of magnetic materials with perpendicular magnetic anisotropy (PMA) as well as the application of a small in-plane magnetic field along the current direction to electrically reverse the magnetization [3,4,[14][15][16][17][18][19][20][21]. I...

Anomalous spin-orbit torque switching in synthetic antiferromagnets

“…Recently, it has been experimentally observed that an in-plane field can result in asymmetric domain expansion in HM/FM structures [12,[23][24][25][43][44][45]. Here we propose a switching model to explain the AMS directly arising from the asymmetric domain expansion.…”

“…Therefore σ and the switching directions in Pt/ferromagnet (Pt/FM) and Ta/FM structures are opposite [2][3][4]8,10,[12][13][14][15][16][17]. So far all reported SOT switchings are the SOT switchings of a single ferromagnet [2][3][4]12,14,18,[23][24][25]27], in which reversing either current or in-plane field is necessary to switch magnetization [2][3][4]12,14,18,[23][24][25]27] and the switching rule shown in Figs. 1(a) and 1(b) is well obeyed.…”

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

“…Recent reports have confirmed that such a surface state is intact in Bi 2 Se 3 covered with Fe (Honolka et al, 2012;Scholz et al, 2012) or Co (Ye et al, 2012) with in-plane magnetic anisotropy. Spin-charge coupling effects have been reported by spin pumping (Deorani et al, 2014;Jamali et al, 2015;Kondou et al, 2015;Rojas-Sánchez et al, 2016;Shiomi et al, 2014) and magnetoresistance measurements (Ando, 2014;Li et al, 2014;Yasuda et al, 2016).…”

Enhanced Spin-Orbit Torque via Modulation of Spin Current Absorption

“…Conventional spin transfer torque (STT) utilizes the spin polarized current to transfer angular momentum from one FM to another FM [5,6], and it has been applied to various spintronic devices such as a magnetic random access memory (MRAM) [7][8][9] and race-track domain wall memory [10]. Recently emerging spin-orbit torque (SOT) opens a new prospect in the magnetization manipulation of the HM=FM bilayers [1,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. In a SOT device, the electrons flowing in a HM layer with strong spin-orbit coupling are spin polarized and the subsequent spin current transfers its angular momentum to the adjacent FM.…”