Strong Damping‐Like Spin‐Orbit Torque and Tunable Dzyaloshinskii–Moriya Interaction Generated by Low‐Resistivity Pd_1−xPt_x Alloys

Abstract

Despite their great promise for providing a pathway for very efficient and fast manipulation of magnetization, spin-orbit torque (SOT) operations are currently energy inefficient due to a low damping-like SOT efficiency per unit current bias, and/or the very high resistivity of the spin Hall materials. This work reports an advantageous spin Hall material, Pd 1−x Pt x , which combines a low resistivity with a giant spin Hall effect as evidenced with three independent SOT ferromagnetic detectors. The optimal Pd 0.25 Pt 0.75 alloy has a giant internal spin Hall ratio of >0.60 (damping-like SOT efficiency of ≈0.26 for all three ferromagnets) and a low resistivity of ≈57.5 µΩ cm at a 4 nm thickness. Moreover, it is found that the Dzyaloshinskii-Moriya interaction (DMI), the key ingredient for the manipulation of chiral spin arrangements (e.g., magnetic skyrmions and chiral domain walls), is considerably strong at the Pd 1−x Pt x /Fe 0.6 Co 0.2 B 0.2 interface when compared to that at Ta/Fe 0.6 Co 0.2 B 0.2 or W/Fe 0.6 Co 0.2 B 0.2 interfaces and can be tuned by a factor of 5 through control of the interfacial spin-orbital coupling via the heavy metal composition. This work establishes a very effective spin current generator that combines a notably high energy efficiency with a very strong and tunable DMI for advanced chiral spintronics and spin torque applications.

Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au0.25Pt0.75

“…The nonvolatile SOT-MRAMs can have long data retention, zero standby power, and fast and reliable write. 35). [1] Recent harmonic response measurements on Au 1−x Pt x /Co bilayers [18,19] have indicated that the Au 0.25 Pt 0.75 alloy can be a particularly compelling spin Hall metal for energy-efficient SOT applications due to the combination of a relatively low resistivity (ρ xx ≈ 80 µΩ cm) with a strong antidamping SOT efficiency (ξ DL j ≈ 0.3-0.…”

“…For example, for the pulse width of 200 ps (1 ns), the required switching current for the Au 0.25 Pt 0.75 device is 6I ∞ (2I ∞ ), markedly smaller than 90I ∞ (20I ∞ ) predicted by the macrospin simulation (see Figure 2b). There is also strong interfacial Dzyaloshinskii-Moriya interaction (DMI) [35] and magnetic roughness (variations of thickness and interfacial magnetic anisotropy field) [22] at the Pt (alloy)/ FM interfaces, which should enhance the magnetic nonuniformity. Here, we attribute the observed ultrafast switching mainly to the enhanced nonuniform micromagnetic dynamics within the free layer of our devices.…”

Enhancing Spin-Orbit Torque by Strong Interfacial Scattering From Ultrathin Insertion Layers

“…DL for Pt/ferromagnet (FM) systems is ~0.08 where ρxx = 20 μΩ cm [16]. Recently, impurity scattering has been demonstrated to increase DL via enhancing ρxx [17][18][19][20]. However, in all the previous work the increase of DL was limited (e.g., to DL = 0.12-0.3 for 4 nm Pt alloys) due to a fast decrease in σSH with doping level [19] or/and only a weak enhancement of ρxx [17,18].…”

“…Recently, impurity scattering has been demonstrated to increase DL via enhancing ρxx [17][18][19][20]. However, in all the previous work the increase of DL was limited (e.g., to DL = 0.12-0.3 for 4 nm Pt alloys) due to a fast decrease in σSH with doping level [19] or/and only a weak enhancement of ρxx [17,18]. Exploring new enhancement strategies that can better optimize the trade-offs between ρxx and TintσSH is of both fundamental interest and technological urgency (e.g., for low-power magnetic memories, logic, and oscillators).…”

Effective Spin-Mixing Conductance of Heavy-Metal–Ferromagnet Interfaces

“…Here θSH is the spin Hall ratio of the HM. For SOT experiments [20][21][22][23], the drift-diffusion analysis [4,17] predicts an interfacial spin transparency [19] Tint = 2 eff ↑↓ /GHM ≤ 1 (2) when the HM thickness d >> λs and the interfacial spin-orbit coupling (ISOC) is negligible. Therefore, the measured dampinglike SOT efficiency per unit applied electric field is DL ≈ 2 eff ↑↓ θSH/ρxxGHM.…”