Abstract
Iridium is a very promising material for spintronic applications due to its interesting magnetic properties such as large RKKY exchange coupling as well as its large spin-orbit coupling value. Ir is for instance used as a spacer layer for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, only a few studies of the spintronic parameters of this material have been reported. In this paper, we present inverse spin Hall effect - spin pumping ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the values of the effective spin Hall angle, the spin diffusion length within iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to have reliable results, we performed the same experiments on CoFeB/Pt bilayers, which behavior is well known due to numerous reported studies. Our experimental results show that the spin diffusion length within iridium is 1.3 nm for resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow \downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle of iridium has the same sign than the one of platinum and is evaluated at 26% of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt and 2% for Ir. These relevant parameters shall be useful to consider Ir in new concepts and devices combining spin-orbit torque and spin-transfer torque.
Highlights
Iridium is a very promising material for spintronic applications
We can use the remark from Ref. [26], stating that in the case of Pt, given the results reported in the literature, the product of the effective spin Hall angle and the spin diffusion length, θSH × ls f, is a quantity that is nearly independent of the technique or the setup used, and its effective value is estimated to be close to 0.19 nm
We have described an approach that enables the measurement of the spin Hall angle of a material with respect to another one
Summary
Iridium is a very promising material for spintronic applications. Its properties include large spin-orbit coupling [1], large Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange coupling [2], and strong interface contribution to perpendicular magnetic anisotropy (PMA) [3,4,5,6] and to interfacial Dzyaloshinskii-Moriya interaction [7]. From the peaks at resonance, several materials properties can be deduced From this ISHE spin pumping voltage, the resonance magnetic field Hres as a function of the frequency f of the rf excitation applied to the sample gave us information about the ferromagnetic layer excited. The relationship between these parameters is described by the Kittel law [36], as presented in Fig. 2(b): f. From the measurement of the spin pumping voltage as a function of the applied field [Fig. 2(a)] one can determine the linewidth H of the voltage peaks to estimate the magnetic damping α of the materials.
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