Highly Efficient Spin–Orbit Torque and Switching of Layered Ferromagnet Fe₃GeTe₂

Abstract

Among van der Waals (vdW) layered ferromagnets, Fe 3 GeTe 2 (FGT) is an excellent candidate material to form FGT/heavy metal heterostructures for studying the effect of spin-orbit torques (SOT). Its metallicity, strong perpendicular magnetic anisotropy built in the single atomic layers, relatively high Curie temperature (T c ~ 225 K) and electrostatic gate tunability offer a tantalizing possibility of achieving the ultimate high SOT limit in monolayer all-vdW nanodevices. In this study, we fabricate heterostructures of FGT/Pt with 5 nm of Pt sputtered onto the atomically flat surface of ~ 15 -23 nm exfoliated FGT flakes. The spin current generated in Pt exerts a damping-like SOT on FGT magnetization. At ~2.5x10 11 A/m 2 current density, SOT causes the FGT magnetization to switch, which is detected by the anomalous Hall effect of FGT. To quantify the SOT effect, we measure the second harmonic Hall responses as the applied magnetic field rotates the FGT magnetization in the plane. Our analysis shows that the SOT efficiency is comparable with that of the best heterostructures containing three-dimensional (3D) ferromagnetic metals and much larger than that of heterostructures containing 3D ferrimagnetic insulators. Such large efficiency is attributed to the atomically flat FGT/Pt interface, which demonstrates the great potential of exploiting vdW heterostructures for highly efficient spintronic nanodevices.

Efficient Spin‐Orbit Torque Switching of the Semiconducting Van Der Waals Ferromagnet Cr2Ge2Te6

“…Figure e puts our experimental findings on SOT switching into the context of previously reported data on other hetero stacks. It is apparent that metallic HM/FM heterostructures such as Ta/CoFeB or Pt/FGT require in general high critical current densities of around 10 7 A cm –2 for field‐assisted SOT switching as a result of current shunting through the magnet and large M s values of the magnets used. On the other hand, integration of insulating FMs such as TMIG or usage of TI as GSHE material that exhibits large spin Hall angles can reduce the required critical current densities to ≈10 6 A cm –2 .…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…Comparing with prior switching devices, a better switching efficiency of 2.2 has been found in this case . According to Figure E, the critical current density required to switch the FGT magnetization strongly depends on the magnitude of an in‐plane applied magnetic field …”

“…E, Effective switching current as a function of in‐plane negative and positive bias field. The color scale shows the ratio of switching resistance to the absolute value of the anomalous Hall resistance…”

“…For instance, the group of Xu et al has studied a CrI 3 /WSe 2 heterostructure, via which a large interfacial exchange energy, equivalent to the effect of a 13 T magnetic field, has been revealed by circularly polarized photoluminescence measurements above and below the Curie temperature of CrI 3 at zero magnetic field, due to lifting of the valley degeneracy of WSe 2 via magnetic proximity with CrI 3 . Besides combining with 2D materials, paramagnetic Pt/FGT heterostructures have also been reported . It has been demonstrated that the spin current generated in the Pt layer could switch the magnetization of the FGT layer by exerting a damping‐like spin‐orbital torque.…”

“…114 Besides combining with 2D materials, paramagnetic Pt/FGT heterostructures have also been reported. 110,115 It has been demonstrated that the spin current generated in the Pt layer could switch the magnetization of the FGT layer by exerting a damping-like spin-orbital torque. Comparing with prior switching devices, a better switching efficiency of 2.2 has been found in this case.…”