Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces

TL;DR

This paper introduces a new method to induce significant magneto-optical effects in gold by injecting hot spin-polarized electrons across Fe/Au interfaces, enabling ultrafast control without external magnetic fields.

Contribution

It presents a novel ultrafast spin injection technique that modulates gold's magneto-optical properties, supported by experimental and ab initio theoretical analysis.

Findings

Majority electrons propagate at ~1 nm/fs in Au

Decay length of injected electrons is ~100 nm

The method enables femtosecond control of magneto-optical effects

Abstract

We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the decay length on the order of 100 nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.