Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers

Abstract

Pure spin current, a flow of spin angular momentum without flow of any accompanying net charge, is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM) with strong spin–orbit coupling, such as Pt or Ta. The other utilizes the collective motion of magnetic moments or spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we demonstrate in NM/MI/NM trilayers that these two types of spin currents are interconvertible across the interfaces, predicated as the magnon-mediated current drag phenomenon. The transmitted signal scales linearly with the driving current without a threshold and follows the power-law Tn with n ranging from 1.5 to 2.5. Our results indicate that the NM/MI/NM trilayer structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics.

Conversion of electronic to magnonic spin current at a heavy-metal magnetic-insulator interface

“…This method requires a large charge current density in Pt to overcome the magnetization damping and the effect is highly nonlinear. An alternative proposal was suggested theoretically by S. Zhang et al [15] and subsequently ap- * guogh@mail.csu.edu.cn proved experimentally for devices with different geometries [16][17][18][19][20]: Instead of exciting spin waves through the spin transfer torque, thermal magnons are created or annihilated based on the electron-magnon interaction directly at the normal metal-magnetic insulator interface. The non-equilibrium thermal magnons diffuse away or towards the interface, generating thus a magnonic spin current.…”

“…Hence, ways to trigger magnonic spin current electrically are highly advantageous. One way to achieve that is via the inter-conversion between the electronic and magnonic spin currents at interfaces [2,[15][16][17][18][19][20]. Till now, basically two methods accomplish the charge to magnon conversion.…”

“…[15][16][17][18]28]. For θ = 0, the electron spins are antiparallel to the thermal magnon's spins oriented opposite to the local magnetization, and magnons are annihilated due to the transfer of angular momentum.…”

“…An explanation of this asymmetry was formulated in terms of the spin Seebeck effect: The joule heating in the Pt layer generates a temperature gradient at the Pt / YIG interface and a positive magnon accumulation leads to the flow of magnons away from the interface [16,18].…”

Platinum/yttrium iron garnet inverted structures for spin current transport

“…[9][10][11] To form bilayers, a thin polycrystalline metal layer is typically deposited on top of YIG by sputtering, which results in reasonably good interfaces for spin current transport. 7,8,12 For some studies such as the magnon-mediated current drag, 13,14 sandwiches of metal/YIG/metal are required, in which YIG needs to be both magnetic and electrically insulating. However, high-quality bilayers of the reverse order, i.e.…”