Terahertz spin ratchet effect in magnetic metamaterials

TL;DR

This paper demonstrates terahertz radiation-induced spin ratchet currents in magnetic metamaterials, revealing polarization-independent and dependent effects driven by near-field diffraction and electron scattering at antidot boundaries.

Contribution

It introduces a microscopic theory explaining spin ratchet and trigonal photocurrents in magnetic metamaterials, highlighting the role of antidot geometry and magnetization.

Findings

Polarization-independent spin ratchet current observed

Trigonal spin photocurrent depends on electron scattering at antidots

Microscopic theory links currents to near-field diffraction and magnetization effects

Abstract

We report on spin ratchet currents driven by terahertz radiation electric fields in a Co/Pt magnetic metamaterial formed by triangle-shaped holes forming an antidots lattice and subjected to an external magnetic field applied perpendicularly to the metal film plane. We show that for a radiation wavelength substantially larger than the period of the antidots array the radiation causes a polarization-independent spin-polarized ratchet current. The current is generated by the periodic asymmetric radiation intensity distribution caused by the near-field diffraction at the edges of the antidots, which induces spatially inhomogeneous periodic electron gas heating, and a phase-shifted periodic asymmetric electrostatic force. The developed microscopic theory shows that the magnetization of the Co/Pt film results in a spin ratchet current caused by both the anomalous Hall and the anomalous Nernst effects. Additionally, we observed a polarization-dependent trigonal spin photocurrent, which is caused by the scattering of electrons at the antidot boundaries resulting in a spin-polarized current due to the magnetization. Microscopic theory of these effects reveals that the trigonal photocurrent is generated at the boundaries of the triangle antidots, whereas the spin ratchet is generated due to the spatially periodic temperature gradient over the whole film. This difference causes substantially different hysteresis widths of these two currents.