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Coupling up of spins and lattice The development of spintronics and magnetic data storage relies on understanding and controlling the dynamics of magnetic excitations within a material. Of crucial importance for practical applications is how fast the magnetization can be switched. Mashkovich et al . report the use of ultrafast terahertz radiation to create magnon excitations in the antiferromagnet cobalt difluoride that can then be coupled with phonon excitations (see the Perspective by Juraschek and Narang). Using light to control coupling between the spins and the lattice provides a route to manipulate magnetization in antiferromagnetic materials on ultrafast time scales. —ISO

A nearly single cycle intense terahertz (THz) pulse with peak electric and magnetic fields of 0.5 MV=cm and 0.16 T, respectively, excites both modes of spin resonances in the weak antiferromagnet FeBO 3 . The high frequency quasiantiferromagnetic mode is excited resonantly and its amplitude scales linearly with the strength of the THz magnetic field, whereas the low frequency quasiferromagnetic mode is excited via a nonlinear mechanism that scales quadratically with the strength of the THz electric field and can be regarded as a THz inverse Cotton-Mouton effect. THz optomagnetism is shown to be more energy efficient than similar effects reported previously for the near-infrared spectral range.

We demonstrate, both theoretically and experimentally, that a sandwich-type structure consisting of a thin LiNbO3 slab and Si prism outcoupler can be an efficient convertor of unamplified laser pulses into broadband terahertz radiation. Pumping a 1 cm long sandwich structure with a 35 μm thick LiNbO3 slab by 8 nJ, 100 fs optical pulses from Ti:sapphire oscillator we achieved the conversion efficiency of 0.8×10−4, i.e., two orders of magnitude higher than in the conventional generation scheme with ZnTe crystal. Using laser oscillator as a pump has an advantage of high repetition rate and, therefore, potentially high signal-to-noise ratio (∼50 dB in our experiment).

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