Spin Oscillations in Antiferromagnetic NiO Triggered by Circularly Polarized Light (1003.0820v1)

Abstract: Coherent spin oscillations were non-thermally induced by circularly polarized pulses in fully compensated antiferromagnetic NiO. This effect is attributed to an entirely new mechanism of the action, on the spins, of the effective magnetic field generated by an inverse Faraday effect. The novelty of this mechanism is that spin oscillations are driven by the time derivative of the effective magnetic field acting even on "pure" antiferromagnets with zero net magnetic moment in the ground state. The measured frequencies (1.07 THz and 140 GHz) of the spin oscillations correspond to the out-of-plane and in-plane modes of antiferromagnetic magnons.

Spin Oscillations in Antiferromagnetic NiO Triggered by Circularly Polarized Light

This paper presents an investigation into coherent spin oscillations induced in antiferromagnetic NiO via circularly polarized light. The primary focus is on the novel mechanism facilitated by the inverse Faraday effect (IFE), which enables non-thermal excitation of spin dynamics in pure antiferromagnetic systems with zero net magnetic moment. The frequencies of the induced spin oscillations, at 1.07 THz and 140 GHz, correspond to the out-of-plane and in-plane modes of antiferromagnetic magnons, respectively.

Key Findings and Methodology

The researchers employed pump-probe experiments to observe spin oscillations in NiO, a fully compensated antiferromagnet. These experiments revealed two distinct regimes:

1. Ultrafast Magneto-Optical Effects: In the sub-picosecond regime (around 1 ps delay), the paper observed significant polarization rotation, indicative of femtomagnetic effects where photon angular momentum directly influences the spin dynamics.
2. Spin Oscillation Dynamics: At longer time delays (exceeding 10 ps), damped oscillations were attributed to the spin-wave modes of antiferromagnetic magnons driven by the time derivative of the effective magnetic field (IFE). Amplitudes were calculated based on the form of the pulse field components.

Theoretical Implications

Theoretical models, particularly the $\sigma$-model, form the foundation for understanding the spin dynamics in AFMs. This model highlights the interaction between sublattice magnetizations under the influence of an effective magnetic field generated by circularly polarized light. Notably, the oscillations observed in the paper are dictated by the time derivative of this field, highlighting a torque effect on the antiferromagnetic vector rather than static magnetization contributions.

Practical Implications

This research opens avenues for rapid control of spin dynamics in antiferromagnetic materials, offering pathways for the development of spintronic devices that leverage ultrafast optical switching. NiO, with its established antiferromagnetic properties and feasibility for room-temperature operations, holds promise as a candidate for devices requiring rapid magnetism control in the THz frequency range.

Speculations on Future Developments

Future research could investigate similar non-thermal mechanisms in other antiferromagnetic materials, potentially broadening the scope of applications in spintronics. A detailed exploration of spin-orbital interactions within the context of photon-induced magneto-optical effects may further enhance the control and utilization of femtomagnetic phenomena in technological applications. Moreover, integrating these findings with existing spintronic architectures could pave the way for energy-efficient and high-speed data processing solutions.

The insights provided by this paper highlight significant advancements in antiferromagnetic spin control, promising further developments in the theoretical understanding and practical application of ultrafast magnetic phenomena.