The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures

TL;DR

This study investigates how the interface quality affects ultrafast spin transfer in antiferromagnet-heavy metal heterostructures, demonstrating optically induced picosecond spin currents and their temperature-dependent behavior.

Contribution

It provides new insights into the role of interface properties in ultrafast spin transfer, supported by experimental THz spectroscopy and a theoretical exchange model.

Findings

Spin transfer occurs at the AFI/Pt interface within picoseconds.

Temperature influences spin transfer efficiency via magnon gap opening.

Model confirms spin exchange as the mechanism for observed phenomena.

Abstract

Interfaces between heavy metals (HMs) and antiferromagnetic insulators (AFIs) have recently become highly investigated and debated systems in the effort to create spintronic devices able to function at terahertz frequencies. Such heterostructures have great technological potential because AFIs can generate sub-picosecond spin currents which the HMs can convert into charge signals. In this work we demonstrate an optically induced picosecond spin transfer at the interface between AFIs and Pt using time-resolved THz emission spectroscopy. We select two antiferromagnets in the same family of fluoride cubic perovskites, KCoF3 and KNiF3, whose magnon frequencies at the centre of the Brillouin zone differ by an order of magnitude. By studying their behaviour with temperature we correlate changes in the spin transfer efficiency across the interface to the opening of a gap in the magnon density of states below the N\'eel temperature. Our observations are reproduced in a model based on the spin exchange between the localized electrons in the antiferromagnet and the free electrons in Pt. These results constitute an important step in the rigorous investigation and understanding of the physics of AFIs/HMs interfaces on the ultrafast timescale.