Nonthermal optical control of magnetism and ultrafast laser-induced spin dynamics in solids

Ultrafast laser control of magnetism is one of the most exciting and challenging issues in physics and technology. Such a technique may provide the solution to the need for an ever increasing speed of data storage and manipulation. This review summarizes the recent progress in the study of ultrafast nonthermal effects of light on magnetic materials. Beginning with an introduction, the paper focuses on three main routes for laser control of magnetism. First, it is shown that due to the inverse, opto-magnetic Faraday effect, circularly polarized light may magnetize a medium. Microscopically, this effect is explained in terms of stimulated Raman scattering, where a spin-flip process requires neither annihilation of a photon, nor loss of its angular momentum. The feasibility of the inverse Faraday effect in magnetically ordered materials is demonstrated on the examples of orthoferrites and garnets. In particular, the effect of a 100 fs optical pulse on spins in DyFeO3 is found to be equivalent to an equally short magnetic field pulse up to 1 T. Second, linearly polarized 100 fs laser pulses are shown to create a long-lived modification of the magnetocrystalline anisotropy in magnetic garnets via optically induced electron transfer between nonequivalent ion sites. Third, we show that a combination of two pump pulses and nonthermal effects can lead to coherent control of magnetization dynamics and ultrafast magnetization switching. The review concludes with a summary and an outlook to the feasibility of laser control of magnetism in a broad class of materials.