Excitation of coupled spin\u2013orbit dynamics in cobalt oxide by femtosecond laser pulses

Takuya Satoh,Akitoshi Koreeda,B A Ivanov,Ryugo Iida,Yasuhiro Fujii,Kazuo Kuroda,Tsutomu Shimura,Takuya Higuchi,V I Butrim,Hiroaki Ueda

doi:10.1038/s41467-017-00616-2

Abstract

Ultrafast control of magnets using femtosecond light pulses attracts interest regarding applications and fundamental physics of magnetism. Antiferromagnets are promising materials with magnon frequencies extending into the terahertz range. Visible or near-infrared light interacts mainly with the electronic orbital angular momentum. In many magnets, however, in particular with iron-group ions, the orbital momentum is almost quenched by the crystal field. Thus, the interaction of magnons with light is hampered, because it is only mediated by weak unquenching of the orbital momentum by spin–orbit interactions. Here we report all-optical excitation of magnons with frequencies up to 9 THz in antiferromagnetic CoO with an unquenched orbital momentum. In CoO, magnon modes are coupled oscillations of spin and orbital momenta with comparable amplitudes. We demonstrate excitations of magnon modes by directly coupling light with electronic orbital angular momentum, providing possibilities to develop magneto-optical devices operating at several terahertz with high output-to-input ratio.

Highlights

Ultrafast control of magnets using femtosecond light pulses attracts interest regarding applications and fundamental physics of magnetism
We demonstrate excitations of magnon modes by directly coupling light with electronic orbital angular momentum, providing possibilities to develop magneto-optical devices operating at several terahertz with high output-to-input ratio
In CoO, the coupled spin–orbit dynamics provides a complex combination of magnon modes with different symmetries and frequencies

Summary

Introduction

Ultrafast control of magnets using femtosecond light pulses attracts interest regarding applications and fundamental physics of magnetism. In contrast to a recent realization of a non-trivial spin evolution for opaque metallic ferrimagnets[8, 9], non-thermal excitation does not lead to intense heating of the sample This feature attracts particular attention for possible applications of antiferromagnets in magnetic recording and magneto-optical devices, e.g., terahertz radiation sources[10, 11] and optomagnonic read–write transfer[12]. We report highly efficient non-thermal coherent excitation of magnon modes in CoO using femtosecond laser pulses at frequencies up to 9 THz. Symmetry analysis and a theoretical model calculation confirm the excitation of these modes, which consist of coupled dynamics that have comparable amplitudes of the oscillations of spin and orbital angular momenta

Methods

Results

Conclusion