Theoretical investigation of the inverse Faraday effect via a stimulated Raman scattering process

Abstract

We study theoretically the origin and mechanism of the ultrafast inverse Faraday effect, which is a magnetooptical effect, attracting much interest nowadays. Laser-induced subpicosecond spin dynamics in hydrogenlike systems and isolated many-electron atoms are investigated in order to get insight into this process. We show that the stimulated Raman scattering process leads to a change of the magnetic state of a system. We obtain the time evolution of the induced magnetization, its dependencies on laser properties, and the connection with the spin-orbit coupling of a system. DOI: 10.1103/PhysRevB.85.094419 PACS number(s): 75.78. Jp, 78.20.Ls, 75.60.Jk, 42.65.Dr INTRODUCTIONUltrafast optical control of the magnetic state of a medium has recently become a subject of intense research in modern magnetism.1,2 The manipulation of a magnetic order by subpicosecond laser pulses is challenging for the development of novel concepts for high-speed magnetic recording, information processing, and data storage. And at the same time, it reveals fundamental questions on magnetization dynamics and makes it possible to understand the fascinating physics of processes, which happen on subpicosecond time scales.A set of experiments has revealed a direct subpicosecond optical control on magnetization via the inverse Faraday effect, i.e., the process of the generation of a magnetic field by nonlinear polarized light. [3][4][5] In these experiments circularly polarized high-intensity laser pulses several tens of femtoseconds long are used to excite a magnetic system of a sample. [6][7][8][9][10][11][12][13][14] It was shown that such laser pulses act as an effective magnetic field in oxidic materials, which are weak ferromagnets 6-10 and even compensated antiferromagnets 12 and paramagnets. 13 However, the mechanisms of laser-induced magnetization dynamics are still poorly understood in spite of much experimental [6][7][8][9][10][11][12][13][14][15][16][17][18] and theoretical [19][20][21][22][23][24][25][26][27] effort. One of the open questions is the evolution of the magnetic momentum of a medium excited by a laser pulse. 18,21,24 It cannot be answered without the knowledge of the laserinduced transitions, which lead to the change of the magnetic state of a system in the inverse Faraday effect experiments. In order to get a detailed insight into such transitions, we study the stimulated Raman scattering process, which has been suggested to be responsible for this effect. 4,9,20 In this process a laser pulse stimulates an optical transition from the ground state to a virtual excited state, which is split due to some interaction, for example, the spin-orbit coupling. Then the transition back to the ground state is stimulated. But due to the transition to the virtual state, the magnetic state of the electron brought back to the ground state is changed. We simulate this process in our systems at the femtosecond time scale and describe the mechanism of how optical transitions, excited by circularly polarized light, can lead to a change of...

Manipulation of ferromagnets via the spin-selective optical Stark effect

“…28 In the following, we will disregard the band dispersion, a common approximation in theories of Raman scattering 29 that is allowed for low doping levels and/or large detuning. The electric field component of monochromatic light with frequency ω 0 and wave vector q ẑ is E(t) 30 For a laser pulse width of 40-100 fs with a frequency that is not too close to the resonance, the above criterion is satisfied byh/E g ≈ 0.5 fs for our material.…”

Writing and reading of an arbitrary optical polarization state in an antiferromagnet

“…Coherent magnetization control via Raman scattering [10][11][12][13][14][15][16][17][18][19] , in particular, is attracting attention. Typical examples are the inverse Faraday effect (inverse FE) 10 and the inverse Cotton-Mouton effect (inverse CME) 12 , in which circularly and linearly polarized light pulses, respectively, induce an effective magnetic field in a magnetically ordered medium 3 .…”

Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque

“…However, most AOS samples are amorphous [8,9] and are hard to simulate without significant approximations. To this end, a unified understanding is still missing, but several promising mechanisms have been proposed, which include the inverse Faraday effect [7,10], spin-flip stimulated Raman scattering [11,12], magnetic circular dichroism [13], magnetic sublattice competition [14], pure thermal effect [15,16] and ultrafast exchange scattering [17]. Recently, Lambert et al [18] reported AOS in an ultrathin ferromagnetic [Co(0.4 nm)/Pt(0.7 nm)] 3 multilayer.…”