Artificial enhancement of the spin Hall angle of Ge using the interdiffusion of atoms in Co2FeAl0.5Si0.5/n-Ge heterostructures

Abstract

Realizing efficient spin-charge conversion is an important issue in spintronics, especially for the development of low-power-consumption magnetization switching. A spin-charge conversion is generally induced in a nonmagnetic (NM) layer by the inverse spin Hall effect. The spin-charge conversion efficiency, so-called the spin Hall angle θSHE, is limited by the spin-orbit interaction of the NM layer. Thus, artificially enhancing the θSHE to greater than its intrinsic value is difficult. Here, using spin pumping measurements on all-epitaxial single-crystalline heterostructures composed of ferromagnetic (FM) Co2FeAl0.5Si0.5 (CFAS) and an NM n-type Ge, we demonstrate that the θSHE can be strongly enhanced by annealing the sample and the resulting interdiffusion of the atoms within only ~3.7 nm around the CFAS/n-Ge interface. The magnitude of the electromotive force was significantly different between the as-grown and annealed samples as shown in Fig. 1. From these results, θSHE is estimated to be 0.0058–0.0079 for the as-grown sample and 0.015–0.019 for the annealed one at 70–300 K (Fig. 2), which is much larger than the intrinsic value of the θSHE reported for Ge (0.00096–0.002) [1-3] and is comparable to θSHE values reported for Pt. This enhancement is attributed to strong scattering of the spin current in the intermixed layer formed at the interface by annealing. Our results indicate that the θSHE is strongly influenced by the atomic structure of the FM/NM interface, which suggests a new and efficient method to control spin-charge conversion by precise control of the FM/NM interface [4]. This work was partly supported by Grants-in-Aid for Scientific Research (No.18H03860, 19H05616), CREST of JST (No. JPMJCR1777), and the Spintronics Research Network of Japan (Spin-RNJ).