All-Electrical Spin-to-Charge Conversion in Sputtered Bi_xSe_1-x

Abstract

One of the major obstacles to realizing spintronic devices such as MESO logic devices is the small signal magnitude used for magnetization readout, making it important to find materials with high spin-to-charge conversion efficiency. Although intermixing at the junction of two materials is a widely occurring phenomenon, its influence on material characterization and the estimation of spin-to-charge conversion efficiencies are easily neglected or underestimated. Here, we demonstrate all-electrical spinto-charge conversion in Bi x Se 1-x nanodevices and show how the conversion efficiency can be overestimated by tens of times depending on the adjacent metal used as a contact. We attribute this to the intermixing-induced compositional change and the properties of a polycrystal that lead to drastic changes in resistivity and spin Hall angle. Strategies to improve the spin-to-charge conversion signal in similar structures for functional devices are discussed.

Spin‐Orbit Readout Using Thin Films of Topological Insulator Sb2Te3 Deposited by Industrial Magnetron Sputtering

“…The obtained transverse resistance is slightly larger than the one found in a comparable geometry of spin‐orbit readout device [ 16 ] using Bi x Se 1‐ x . A study using heavy metal‐based heterostructures reported a one order of magnitude larger transverse resistance.…”

“…[ 55 ] It is possible to separate these different contributions using a combination of systematic geometric dependencies and finite element simulations. [ 16 ] Here, these spurious effects can be ruled out using the temperature dependence of Δ R xy (Figure 2e). As shown in Figure 1d, the Hall effect is almost temperature independent.…”

“…Moreover, the anomalous Hall effect of CoFe does not vanish at 30 K. [56] Therefore, the ordinary and anomalous Hall effects cannot be at the origin of the observed transverse signal, which therefore comes from a spin-charge interconversion effect in Sb 2 Te 3 . The absence of transverse signal when no TiO x barrier is present proves that a physical separation between the ferromagnetic injection electrode and the Sb 2 Te 3 is necessary to avoid intermixing at the interface, [16] as well as spin-backflow and shunting in the ferromagnet. [12] The obtained transverse resistance is slightly larger than the one found in a comparable geometry of spin-orbit readout device [16] using Bi x Se 1-x .…”

“…Topological insulators are promising materials for the realization of spin-orbit readout devices with high output voltage. These high-resistivity materials [16] are indeed known to exhibit high spin-charge interconversion efficiencies due to the Edelstein-Effect in their topological surface states, [17][18][19] and have already demonstrated their interest for spintronics applications in the context of the spin-orbit torque. [20] The use of these materials for spin-logic circuits is however limited by their fabrication at small-scale by MBE [17,18,21] or by mechanical exfoliation.…”

“…[22,23] In addition, patterning these materials into nanoscale devices is complicated by their sensitivity to conventional nanofabrication processes, [24] so most spin-charge interconversion measurements in topological insulators have been made on microscale devices. Finally, the electrical spin injection into these materials is notoriously difficult due to intermixing effects at the interface with metals [16,25,26] and their low spin conductance caused by their semiconducting nature. [27] Sb 2 Te 3 is one of the first topological insulators discovered, [28] and is known to harbor a high spin-charge interconversion efficiency.…”