Picosecond spin pumping in antiferromagnet-heavy metal heterostructures

Bio

Joseph Barker obtained his PhD at the University of York. He then took a position as an assistant professor in the Theoretical Physics Group of the Institute for Materials Research, Tohoku University in Japan. He moved to Leeds in 2018 as a Royal Society University Research Fellow. His research is into magnetic materials and their applications, specialising in the modelling of magnetic materials using an in-house atomistic spin dynamics package in large scale computer simulations. With his expertise, he aims to perform quantitative calculations of thermodynamic and dynamical behaviour, including non-equilibrium behaviour and phase transitions.

Abstract

Interfaces in heavy metal (HM) - antiferromagnetic insulator (AFI) heterostructures have recently become highly investigated and debated systems in the effort to create spintronic devices that 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-domain 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 Néel 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. Through this comparative study of selected materials, we are able to shine light on the microscopy of spin transfer at picosecond timescales between antiferromagnets and heavy metals and identify a key figure of merit for its efficiency: the magnon gap. Our results are important for progressing in the fundamental understanding of the highly discussed physics of the HM/AFI interfaces, which is the necessary cornerstone for the designing of femtosecond antiferromagnetic spintronics devices with optimized characteristics.

Reference

Kholid FN, Hamara D, Hamdan AF, Nava Antonio G, Bowen R, Petit D, Cowburn R, Pisarev RV, Bossini D, Barker J, Ciccarelli C. "The importance of the interface for picosecond spin pumping in antiferromagnet-heavy metal heterostructures." Nature Communications 14.1 (2023): 538.