In situ Kerr and harmonic measurement in determining current-induced effective fields in MgO/CoFeB/Ta

Abstract

A combination of the harmonic measurement and in situ Kerr imaging was used to experimentally determine the spin–orbit (SO) effective fields in a MgO/CoFeB/Ta structure. Here, we evaluate the SO effective fields through an analytical energy approach by transforming the anomalous Hall effect and planar Hall effect (PHE) voltage into a field dependency while imaging the magnetisation behaviour by differential Kerr microscopy. The analytical fitting to the measurement data indicates the significant coexistence of both a transverse field, , and longitudinal field, , in the longitudinal (HL = –12 Oe, HT = 8 Oe per 106 A cm−2) and transverse (HL = –12 Oe, HT = –17 Oe per 106 A cm−2) measurement schemes, respectively, due to the PHE. Additionally, dendritic-like domains, indicating the influence of the interfacial Dzyaloshinskii–Moriya interaction (DMI) at the CoFeB/Ta interface, were observed by in situ Kerr imaging. Micromagnetic simulations confirm the dendritic domain formation and edge tilting of the magnetisation, as being due to the DMI.

Enhanced Spin-Orbit Torques in Rare-Earth Pt/[Co/Ni]2/Co/Tb Systems

“…At larger t Tb , the shunting of current in Pt greatly decreases; thus, this increases the contributing SHE from the Co/Tb interface. Therefore, [2,25,26], the reference sample gives rise to θ eff SH,Ta ≈ −0.11, which is within a reasonable range of the spin Hall angle reported for Ta [2,27]. Similarly, the spin Hall angle of Tb, θ eff SH,Tb can subsequently be derived from the ξ eff DL such that its value ranges from −0.18 ≤ θ eff SH,Tb ≤ −0.48 for 5 ≤ t Tb ≤ 9 nm.…”

“…The relative efficiency of the DL torque is a commonly used figure of merit for spin Hall material that relates proportionally to the effective spin Hall angle, ξ eff DL ∝ θ eff SH . The ongoing studies of 5d-transition heavy-metal (HM)-ferromagnetic (FM) interfaces has revealed strong intrinsic [23,24] spin Hall effects in Pt (θ eff SH,Pt = +0.09) [2,25,26], β-Ta (θ eff SH,Ta = −0.12) [2,27], and β-W (θ eff SH,W = −0.30) [14]. We continue to pursue the search for alternate spin Hall materials from a class of elements that have been comparatively unexplored, the f -electron rare-earth (R) metals.…”

Dependence of spin-orbit torque effective fields on magnetization uniformity in Ta/Co/Pt structure

“…The measurements were carried out in the wires with stacks of Ta( t nm)/Co(2 nm)/Pt(5 nm), where t = 4, 6, 8 and 10 20 . The fabrication and patterning processes of the wires are described elsewhere 17,20–22 . The SOT fields are quantified as a function of the longitudinal fields in the sample of Ta(4 nm)/Co(2 nm)/Pt(5 nm) 20 .…”

“…The dependence of the two effective fields on the orientation of the magnetization has been studied, especially in materials with perpendicular magnetic anisotropy (PMA) 11–17 . Reported SOT measurements on Ta/CoFeB/MgO structures have shown that the damping-like term H D changed the direction when the magnetization is reversed 12 .…”

Enhanced spin-orbit torque (SOT) and spin accumulation quantification in perpendicularly magnetised systems

“…SOT serves as an efficient alternative for reversal of the magnetisation in the FM layer 36,37,39,117,119,130 and driving of DWs 8,74,121,122,172,173 . The origin of the SOT is attributed to both the spin Hall effect 36,47,61,148,174 (SHE) in the NM layer and the interfacial Rashba effect 48,49,58 . Recently, the f-electron rare-earth (R) metals have drawn increasing attention because of their substantial SHE contribution due to their partially filled f-orbitals 146,149 .…”