2202 IEEE TRANSACTIONS ON MAGNETICS, VOL. 46, NO. 6, JUNE 2010 Inverse Spin-Hall Effect Induced by Spin Pumping in Different Thickness Pt Films Hiroyasu Nakayama , Kazuya Ando , Kazuya Harii , Yosuke Kajiwara , Tatsuro Yoshino , Ken-ichi Uchida , and Eiji Saitoh Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan Department of Applied Physics and Physico-Informatics, Keio University, Yokohama 223-8522, Japan PRESTO, Japan Science and Technology Agency, Sanbancho, Tokyo 102-0075, Japan The inverse spin-Hall effect, conversion of spin currents into electromotive force, has been investigated in Pt thin films with changing the thickness of the Pt films. We measured the electric voltage due to the inverse spin-Hall effect induced by the spin pumping in bilayer systems with different Pt thickness films ( 10, 30, 50, and 75 nm) at room temperature. The experimental results show that the signal induced by the inverse spin-Hall effect is inversely proportional to the Pt thickness , which is well reproduced by a simple equivalent circuit model. Index Terms—Ferromagnetic resonance, inverse spin-Hall effect, spin currents, spin pumping. I. INTRODUCTION S PINTRONICS is a rapidly growing field, which aims to extend the scope of conventional electronics using the spin degree of freedom in solid-state systems [1]–[3]. In this field, the generation and detection of a spin current, a flow of electron spins in a solid, are the essential technology that realizes efficient spin-based magnetic memories and computing devices. In this stream, intense theoretical and experimental interests have been focused on the direct and inverse spin-Hall effects (SHE/ISHE) [4]–[21]. The direct and inverse spin-Hall effects are responsible for the reciprocal conversion between a spin current and a charge current via the spin-orbit interaction. The inverse spin-Hall effect, which converts a spin current into a charge current, has been observed using the spin-pumping [14]–[20] and the non-local method [8]–[11] in films. The spin pumping refers to the generation of spin currents from magnetization dynamics; a precessing magnetization in a ferromagnetic metal induces a spin current in a paramagnetic metal attached to the ferromagnetic metal. The spin pumping method requires only a simple ferromagnetic/paramagnetic bilayer system, making it a key technique for generating and detecting spin currents in a wide range of sample system. To design a high sensitive device using these effects, systematic understanding the affect of sample form is effectual. In this article, we report the observation of the ISHE induced by spin pumping in different thickness Pt films attached to a film. II. EXPERIMENTAL PROCEDURE Fig. 1 shows a schematic illustration of the sample system used in the present study. The samples are films comprising a 10-nm-thick ferromagnetic layer and a Manuscript received October 31, 2009; revised January 13, 2010; accepted January 14, 2010. Current version published May 19, 2010. Corresponding au- thor: H. Nakayama (e-mail: nakayama@imr.tohoku.jp). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2010.2042150 Fig. 1. (a) A schematic illustration of the bilayer system used in the present study. denotes the external magnetic field. , , and denote the thick- ness, the length, and the width of Pt layer, respectively. (b) A schematic illustra- tion of the spin pumping and the inverse spin-Hall effect in the present system. , , , , and denote the microwave magnetic field, the precessing magnetization in the ferromagnetic layer, the spin current generated by the spin pumping, the spin polarization of the spin current, and the electric field induced by the inverse spin-Hall effect, respectively. The white dotted arrow in the para- magnetic layer describes electron motion bent by the spin-orbit interaction in the paramagnetic layer, a motion responsible for inverse spin-Hall effect. paramagnetic Pt layer with the thickness of , 30, 50, and 75 nm. The paramagnetic Pt layer was sputtered on a thermally oxidized Si substrate and then the ferromagnetic layer was evaporated in a high vacuum on the Pt layer. The Pt layer is of the 0.6 mm 3.2 mm rectangle shape and the layer is of the 0.6 mm 1.6 mm rectangle shape. Two elec- trodes are attached to both ends of the Pt layer. For the measure- ment, the sample system is placed near the center of a microwave cavity at which the magnetic-field component of the 0018-9464/$26.00 © 2010 IEEE