Dynamics of photoinduced change of magnetoanisotropy parameter in orthoferrites probed with terahertz excited coherent spin precession

The effects of femtosecond laser excitation on the anisotropy parameter in orthoferrites ErFeO₃ and DyFeO₃ were probed through Faraday rotation induced by coherent spin precession, which was triggered by a terahertz pulse. Through the delayed frequency shift of the precession, gradual change in the anisotropic energy of the iron spins is evidenced. This is attributed to the slow energy transfer from the Fe³⁺0.28em0ex3d electron system to the rare-earth $4f$ electron system, which in turn alters the anisotropy parameter of the Fe³⁺ spins. The result presented here reveals the time dependent spin alignment mechanism in cant-type antiferromagnetic orthoferrites and enables deeper understanding of spin orientation dynamics triggered by electronic excitation.