A 2005 study by Kimel et al. in Nature demonstrates that circularly polarized femtosecond laser pulses can non-thermally excite and coherently control spin dynamics in magnets via the inverse Faraday effect. This effect allows for instantaneous control of magnetization, limited by the pulse width (≈200 fs). Unlike traditional methods that rely on thermal excitation, this approach enables ultrafast, non-thermal manipulation of magnetization, offering new possibilities for applications in magnetic devices. The inverse Faraday effect generates a static magnetization in response to high-intensity laser radiation, with the magnetization direction aligned along the wave vector of the light. This effect is equivalent to the action of an external magnetic field, with right- and left-handed circularly polarized light inducing magnetizations of opposite sign. The magneto-optical susceptibility χ, which governs both the Faraday and inverse Faraday effects, is not restricted by symmetry and is present in all materials, regardless of their structure. The study used dysprosium orthoferrite (DyFeO₃), a rare-earth orthoferrite with a strong spin-orbit interaction, which exhibits a large Faraday rotation. The material was probed using the magneto-optical Faraday effect, revealing two processes: instantaneous changes in the Faraday rotation due to photoexcitation of Fe ions and relaxation back to the high spin ground state, and oscillations of the Fe spins around their equilibrium direction with a period of approximately 5 ps. The helicity of the pump light controlled the sign of the photo-induced magnetization, indicating a direct coupling between spins and photons. The frequency of the spin oscillations increased with temperature, up to 450 GHz at 175 K, while the amplitude decreased. The oscillations were attributed to magnon scattering on phonons and spins of dysprosium ions. The amplitude of the photo-induced oscillations was found to be M = M_S/16, where M_S is the saturation magnetization. The study also showed that the effect of a 200 fs laser pulse on the magnetic system is equivalent to a magnetic field pulse of about 5 T. The results demonstrate that circularly polarized femtosecond laser pulses can non-thermally excite and coherently control spin oscillations in DyFeO₃, offering new insights into ultrafast magnetic excitation and potential applications in magnetic devices. The findings also suggest that the direct effect of light on spontaneous magnetization in other materials and at higher temperatures is feasible.A 2005 study by Kimel et al. in Nature demonstrates that circularly polarized femtosecond laser pulses can non-thermally excite and coherently control spin dynamics in magnets via the inverse Faraday effect. This effect allows for instantaneous control of magnetization, limited by the pulse width (≈200 fs). Unlike traditional methods that rely on thermal excitation, this approach enables ultrafast, non-thermal manipulation of magnetization, offering new possibilities for applications in magnetic devices. The inverse Faraday effect generates a static magnetization in response to high-intensity laser radiation, with the magnetization direction aligned along the wave vector of the light. This effect is equivalent to the action of an external magnetic field, with right- and left-handed circularly polarized light inducing magnetizations of opposite sign. The magneto-optical susceptibility χ, which governs both the Faraday and inverse Faraday effects, is not restricted by symmetry and is present in all materials, regardless of their structure. The study used dysprosium orthoferrite (DyFeO₃), a rare-earth orthoferrite with a strong spin-orbit interaction, which exhibits a large Faraday rotation. The material was probed using the magneto-optical Faraday effect, revealing two processes: instantaneous changes in the Faraday rotation due to photoexcitation of Fe ions and relaxation back to the high spin ground state, and oscillations of the Fe spins around their equilibrium direction with a period of approximately 5 ps. The helicity of the pump light controlled the sign of the photo-induced magnetization, indicating a direct coupling between spins and photons. The frequency of the spin oscillations increased with temperature, up to 450 GHz at 175 K, while the amplitude decreased. The oscillations were attributed to magnon scattering on phonons and spins of dysprosium ions. The amplitude of the photo-induced oscillations was found to be M = M_S/16, where M_S is the saturation magnetization. The study also showed that the effect of a 200 fs laser pulse on the magnetic system is equivalent to a magnetic field pulse of about 5 T. The results demonstrate that circularly polarized femtosecond laser pulses can non-thermally excite and coherently control spin oscillations in DyFeO₃, offering new insights into ultrafast magnetic excitation and potential applications in magnetic devices. The findings also suggest that the direct effect of light on spontaneous magnetization in other materials and at higher temperatures is feasible.