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Extrinsic Spin Hall Effect Induced by Iridium Impurities in Copper

Otani Group

The generation of pure spin currents, flows of only spin angular momentum without charge current, should play an important role in the next generation spintronic devices. The spin Hall effect (SHE) is one of the promising ways to create pure spin currents in nonmagnetic materials without using ferromagnets. Large SHEs have been recently found in noble metals such as Pt and Au and this has triggered an important effort of research on the SHE in metallic materials. The mechanism of such large SHEs, however, has not been figured out yet; whether it is intrinsic or extrinsic, if it is extrinsic whether it stems from the skew scattering mechanism or the side jump one. In this work, we focus on the extrinsic SHE; by adding Ir impurities into a pure Cu wire, we have studied the impurity concentration dependence of the SHE in CuIr alloys. The final goal of the present study is to identify if the major contribution to the SHE is the skew scattering by the Ir impurities and what is the magnitude of the spin Hall (SH) angle which represents the maximum yield of the transformation of charge into spin current density.

Fig.1. (a) Scanning electron microscopy image of a spin Hall device consisting of two Py wires and a CuIr middle wire bridged by a Cu wire. (b) Schematic of the mechanism of ISHE due to the spin absorption effect.

Fig.2. Spin Hall resistivity (ρSHE) as a function of the resistivity induced by Ir impurities (ρimp) for several different concentrations. The inset shows ρimp vs Ir concentration in Cu.

In the present study, we have adopted the spin absorption method using a lateral spin valve structure which consists of two Py wires and a CuIr middle wire bridged by a Cu wire, as shown in Fig. 1 (a). This method is quite powerful for SHE measurements in materials with short spin diffusion length. We perform inverse SHE (ISHE) measurements where pure spin currents generated from Py1 are absorbed into the CuIr middle wire and the deflection in the same direction of the opposite spin-up and spin-down electrons can be detected (see Fig. 1(b)). In order to obtain the SH angle of CuIr, we have to also evaluate its spin diffusion length as well as the spin absorption rate into the CuIr wire. This can be done by measuring the spin valve effect between the two Py wires with and without the CuIr wire (not shown here).

Figure 2 shows the obtained ρSHE as a function of the resistivity induced by the Ir impurities (ρimp). No SHE has been observed when there is no Ir impurity. With increasing the Ir impurity, however, ρSHE increases linearly with ρimp. This linear dependence clearly shows that the skew scattering is the dominant mechanism of the SHE in CuIr. From the slope of the ρSHE vs ρimp curve, it turns out that the SH angle in this system is 2.1% [1], which is consistent with the previous anomalous Hall effect measurement in CuMnIr. This SH angle is definitely larger than that obtained with pure metals [2] and indicates that scattering by impurities is a very promising way to obtain large SH angles.


References
  • Y. Niimi, M. Morota, D. H. Wei, C. Deranlot, M. Basletic, A. Hamzic, A. Fert, and Y. Otani, Phys. Rev. Lett. 106, 126601 (2011).
  • M. Morota, Y. Niimi, K. Ohnishi, D. H. Wei, T. Tanaka, H. Kontani, T. Kimura, and Y. Otani, Phys. Rev. B 83, in press (2011).
Authors
  • bUniversity of Zagreb
  • aUnite Mixte de Physique CNRS/Thales
  • Y. Niimi, M. Morota, D. H. Wei, C. Deranlota, M. Basleticb, A. Hamzicb, A. Ferta, and Y. Otani