Spin Blocking Effect at Ni/Pt Heterojunction

Spin current, the flow of spin angular momentum, can carry and transport energy and/or information without generating Joule heating, which makes spin-based devices expected to be one of the potential aspects for the next generation information processing devices. It is important to investigate the generation, transport, and detection of spins for the development of spin-based devices, in which the spin transport and its related phenomena attract ongoing interests due to the complex interactions between spins and condensed matter systems. Here, spin transport phenomenon is studied at a heterojunction consisting of ferromagnetic metal nickel and nonmagnetic heavy metal platinum, where transport spins are found to be totally blocked. Two series of spin-pumping devices were made in this work which were the yttrium iron garnet (YIG)/Ni/Pt trilayer devices and the contrastive YIG/Ni bilayer devices. YIG was employed as the substrate and the spin-pump layer, on which nickel and platinum films were deposited by dc magnetron sputtering system. Spin currents were generated from YIG and injected into nickel layers by spin pumping technology. Voltage signals corresponding to the inverse spin Hall effect were detected and analyzed comparably for both YIG/Ni/Pt trilayer and YIG/Ni bilayer devices. It is found that the platinum layers in YIG/Ni/Pt trilayer devices only play as charge current shunting but do not contribute to the spin-charge conversion. This implies that the spin current can not transport through the Ni/Pt interface even when the nickel layer is as thin as 1 nm, which means in other words that the spin current is blocked at the Ni/Pt interface. Our result proposes a heterojunction that can block transport spins totally has never been discussed before, which may expand the views and trigger new functions for the development of spin-based devices.