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

Abstract

The interaction between light and magnetism is considered a promising route to the development of energy-efficient data storage technologies. To date, however, ultrafast optical magnetization control has been limited to a binary process, whereby light in either of two polarization states generates (writes) or adopts (reads) a magnetic bit carrying either a positive or negative magnetization. Here, we report how the fundamental limitation of just two states can be overcome, allowing an arbitrary optical polarization state to be written magnetically. The effect is demonstrated using a three-sublattice antiferromagnet-hexagonal YMnO 3 . Its three magnetic oscillation eigenmodes are selectively excited by the three polarization eigenstates of the light. The magnetic oscillation state is then transferred back into the polarization state of an optical probe pulse, thus completing an arbitrary optomagnonic write-read cycle.Two types of interaction between light and magnetism are currently of interest. In the first, the transfer of photon energy to electrons by absorption initiates an interplay of electrons, spins and lattice ions that leads to magnetization changes on timescales down to the femtosecond range 1-3 and may even involve phase transitions 4,5 . Of particular interest for data storage is all-optical magnetization reversal, as observed in a two-sublattice magnetic metal, where thermally activated ultrafast spin waves have been found to play an important role 6 . Optical excitation can also generate coherent spin waves 3,7,8 , which may enter the realm of magnonics 9 .In the second type of interaction, optically stimulated magnetization changes occur, with negligible energy transfer by absorption. Coherent magnetization control via Raman scattering 10-19 , 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 . Coherent processes of this type have a number of potential applications, including information processing, for example, by transferring the optical polarization state into the magnetization of a material.A fully polarized light beam possesses three polarization degrees of freedom: two mutually orthogonal directions of oscillation and the phase between these two components. This is parameterized by three Stokes parameters (S 1,2,3 ) on the Poincaré sphere (Fig. 1a) 20 . Assuming normalization by the light intensity, these are defined as S 1 = cos 2θ, S 2 = sin 2θ cosψ and S 3 = sin 2θ sin ψ, where θ and ψ are the angles parameterizing the complex amplitudes of the light (E x = E 0 cos θ, E y = E 0 sin θe iψ ). Binary light-matter information transfer so far uses only two of this infinite number of photonic states. Light with, for example, S 3 = ±1 generates a positive or negative magnetization bit. This fundamental limitation is overcome by employing all three de...

Antiferromagnetic spintronics

“…[68][69][70][71][72] For example, picosecond-scale reorientation of the antiferromagnetic spin-axis was reported in an optical pump-and-probe study of a rare-earth orthoferrite. 68 The origin of the generated staggered field was different than in current induced spin torques discussed above.…”

Nonlinear spin control by terahertz-driven anisotropy fields

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Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations 5,11 .

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Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide

“…Achieving this goal is expected to reveal fascinating fundamental many-body physics and to enable disruptive technology for information processing at optical clock rates . A variety of promising magneto-optical control schemes has been developed in recent years, including the inverse Faraday effect and Raman-type nonlinear optical processes [2,4,5,[7][8][9][10][11][12][13][14] as well as optical modification of the exchange interaction [15][16][17]. Although these techniques have revolutionized our understanding of ultrafast spin dynamics, the lion share of the photon energy of the visible or near-infrared pump light is idle with respect to the lightspin interaction, and the dissipation of the large excess energy represents a major challenge.…”