Magnetization switching through giant spin–orbit torque in a magnetically doped topological insulator heterostructure (original) (raw)

Here we demonstrate experimentally the magnetization switching through giant SOT induced by an in-plane current in a chromium-doped TI bilayer heterostructure. The critical current density required for switching is below 8.9 × 10 4 A cm −2 at 1.9 K. Moreover, the SOT is calibrated by measuring the e ective spin-orbit field using second-harmonic methods. The e ective field to current ratio and the spin-Hall angle tangent are almost three orders of magnitude larger than those reported for HMFHs. The giant SOT and e cient current-induced magnetization switching exhibited by the bilayer heterostructure may lead to innovative spintronics applications such as ultralow power dissipation memory and logic devices. R ecently, heavy metals (for example, Pt, Ta) with strong SOC have been used to generate spin currents by passing an in-plane charge current to control the magnetization dynamics in an adjacent ferromagnet layer (for example, Co, CoFeB; refs 1-12). Such spin currents, arising from either the spin-Hall effect 1-3,13,14 within the heavy metals or the Rashba effect at the interfaces 7-10,14-20 , can apply efficient spin torques to the ferromagnet, and result in current-induced magnetization manipulation 2,6,7,9-12 and even switching 1,3,8 . Although the underlying mechanisms of the SOTs are still debated 1,4,14 , the ability to manipulate magnetic moments with lateral current has shown promising applications in miniaturized magnetic memory and logic devices, and more appropriate material/structure to generate these SOTs still deserves further investigation. Besides heavy metals, TIs (refs 21-23), in which the SOC is large enough to invert the band structure 24 , are expected to be the most promising candidates to exploit the SOTs when coupled to magnetic moments . In addition, the recently demonstrated magnetism in magnetically doped TIs (for example, Cr-doped TIs; refs 28-34) makes it accessible to study the SOTs in the TI/magnetic-TI bilayer heterostructures . Here, we demonstrate the magnetization switching by in-plane current injection into epitaxial TI/Crdoped TI bilayer films. Using the second-harmonic analysis 4,5 of the anomalous Hall effect (AHE) resistance, we calibrate the effective spin-orbit field arising from the SOT. Most importantly, we find that the effective field to current ratio, as well as the spin-Hall angle tangent, is nearly three orders of magnitude larger than those reported in HMFHs so far. This giant SOT, together with the current-induced switching behaviour, suggests that magnetically doped TI heterostructures could potentially be the materials/structures to generate SOTs with efficiency beyond today's HMFHs.