Realization of a Room-Temperature Spin Dynamo: The Spin Rectification Effect

We demonstrate a room-temperature spin dynamo where the precession of electron spins in ferromagnets converts energy from microwaves to a bipolar current of electricity. The $\mathrm{\text{current}}/\mathrm{\text{power}}$ ratio is at least 3 orders of magnitude larger than that found previously for spin-driven currents in semiconductors. The observed bipolar nature and intriguing symmetry are fully explained by the spin rectification effect via which the nonlinear combination of spin and charge dynamics creates dc currents.

Figure 1

(a) Faraday’s dynamo with a revolving copper disk converts energy from rotation to a current of electricity. (b) Spin dynamo with a FM strip converts energy from spin precession to a bipolar current of electricity. (c) Diagram of the spin dynamo structure with Py strips placed in slots between the ground (G) and signal (S) lines of a coplanar waveguide. (d) Top view micrograph of a device.

Figure 2

Bipolar dc currents measured as a function of the magnetic field $H$ applied with angles (a) $\alpha =-1°$, $\beta =0$, (b) $\alpha =1°$, $\beta =0$, (c) $\alpha =0$, $\beta =-1°$, and (d) $\alpha =0$, $\beta =1°$. The microwave frequency is fixed at 5.4 GHz. The insets summarize the angular dependence of the maximum current measured at $H<0$.

Figure 3

(a) The measured frequency variation (marks) of the resonant features in the $I(\alpha ,H)$ trace in comparison with the calculated dispersions (solid curves) for SSW. (b) AMR trace $R(H)$ measured (thick curves) and calculated (thin curves) at $\alpha =0.5°$, $\beta =0$ and $\alpha =0$, $\beta =-1°$. (c) Current trace $I(\beta ,H)$ measured at $\alpha =0$, $\beta =-1°$ and 5.4 GHz (thin curve) in comparison with the field derivative of the AMR trace $\partial R(H)/\partial H$ (thick curve).

Figure 4

The bipolar dc currents generated by both the FMR (upward triangles) and the $p=2$ SSW (downward triangles) depend linearly on the microwave power. Open triangles are maximum currents measured at 5.4 GHz on a spin dynamo with the Py thickness $d=137\mathrm{nm}$ set at $\alpha =-1°$, $\beta =0$. Solid triangles show both the closed circuit currents (left scale) and the open circuit voltages (right scale) measured at 6 GHz on a second spin dynamo with $d=120\mathrm{nm}$ set at $\alpha =-2°$, $\beta =0$.