Abstract
Spin pumping enables the generation of d.c. and gigahertz-band (GHz-band) voltages from an applied microwave via magnetization dynamics when combined with inverse spin Hall effects. However, generating such voltages in the in-between frequency region, or the megahertz (MHz) band, has been difficult since ferromagnetic resonance usually occurs in the GHz band. Here we show that in spite of GHz-band microwaves applied, MHz-band voltages can be generated by spin pumping with use of nonlinear magnetization dynamics in Y3Fe5O12. The mechanism is ascribed to the MHz-band oscillation of the amplitude of the magnetization precession, which is projected onto a rectified voltage component via spin pumping. The present finding could be useful for frequency down-conversion thanks to the simple and durable structure, continuous-wave operation, and the tunability of an output frequency with low magnetic fields.
Highlights
Spin current is a flow of spin angular momentum of electrons in solids without accompanying charge current[1], which has attracted much attention in spintronics[2, 3]
When steady magnetization precession dynamics is excited in a ferromagnetic material (FM), a d.c. spin current is injected from the FM into the NM through the interface, a phenomenon called spin pumping (Fig. 1a)
Magnetization in a FM, such as a magnetic insulator Y3Fe5O12 (YIG), is known to exhibit typical nonlinear dynamics; when a strong microwave is applied to a FM, a steady magnetization precession motion becomes unstable[22], and auto-oscillation (AO) of the precession amplitude shows up as a nonlinear turbulent bifurcation effect when the microwave power is greater than the AO threshold power[23,24,25,26,27,28,29,30,31]
Summary
Spin current is a flow of spin angular momentum of electrons in solids without accompanying charge current[1], which has attracted much attention in spintronics[2, 3]. When steady magnetization precession dynamics is excited in a FM, a d.c. spin current is injected from the FM into the NM through the interface, a phenomenon called spin pumping (Fig. 1a). By using a NM with strong spin-orbit interaction, such as platinum (Pt), the spin current injected in the NM is converted into voltage via the inverse spin Hall effect[12, 13] (ISHE) caused by the spin-orbit interaction[14,15,16,17,18,19,20,21]. We show that the AO of the precession amplitude can be converted into a voltage oscillation of a much lower frequency, Ω, inside a material exhibiting spin pumping (Fig. 1b). By introducing spin pumping and ISHE into magnetization AO, we demonstrated huge frequency conversion from a microwave with the magnetization-precession frequency into an electric voltage oscillation with the frequency Ω
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