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.Light pulses can control magnetism in a material, and the effective creation of magnetic oscillations leads to spintronic devices with higher efficiency. Here, the authors increase the efficiency of magnon excitation by using a material in which orbital angular momenta are not quenched.
ABSTRACT
Coherent spin oscillations were nonthermally induced by circularly polarized pulses in the fully compensated antiferromagnet NiO. This effect is attributed to the action of the effective magnetic field generated by an inverse Faraday effect on the spins. The novelty of this mechanism is that spin oscillations are driven by the time derivative of the effective magnetic field which acts even on "pure" antiferromagnets with zero net magnetic moment in the ground state. The measured frequencies (1.07 THz and 140 GHz) correspond to the out-of-plane and in-plane modes of antiferromagnetic spin oscillations.
