Ultrafast Faraday effect and the dynamics of the antiferromagnet-paramagnet phase transition in FeBO$_3$

The optical pump-probe technique using ultrashort laser pulses with a photon energy of 1.55 eV was used to study the dynamics of the antiferromagnet-paramagnet phase transition in FeBO$_3$. The Faraday magneto-optical effect was measured with a time resolution of 100 fs, and signal transients were observed as functions of sample temperature. The rate of photoinduced phase transition was shown to be limited by the phonon-magnon relaxation rate with a characteristic time of 700 ps. The subpicosecond dynamics of Faraday rotation is not associated with the destruction of magnetic order but is caused by electron photoexcitation and recombination.