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Experimental observation of the optical spin transfer torque

Nature Physics volume 8, pages 411–415 (2012)Cite this article

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Abstract

The spin transfer torque is a phenomenon in which angular momentum of a spin polarized electrical current entering a ferromagnet is transferred to the magnetization. The effect has opened a new research field of electrically driven magnetization dynamics in magnetic nanostructures and plays an important role in the development of a new generation of memory devices and tunable oscillators. Optical excitations of magnetic systems by laser pulses have been a separate research field the aim of which is to explore magnetization dynamics at short timescales and enable ultrafast spintronic devices. We report the experimental observation of the optical spin transfer torque, predicted theoretically several years ago, building the bridge between these two fields of spintronics research. In a pump-and-probe optical experiment we measure coherent spin precession in a (Ga, Mn)As ferromagnetic semiconductor excited by circularly polarized laser pulses. During the pump pulse, the spin angular momentum of photo-carriers generated by the absorbed light is transferred to the collective magnetization of the ferromagnet. We analyse quantitatively the observed magnetization dynamics triggered by the optical spin transfer torque using independently determined micromagnetic parameters and magneto-optical coefficients of the studied (Ga, Mn)As.

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Figure 1: Schematic illustration of the optical spin transfer torque.
Figure 2: Experimental observation of the optical spin transfer torque.
Figure 3: Absence of inverse magneto-optical effect and polarization-independent excitations.
Figure 4: Helicity-dependent and polarization-independent signals at different piezovoltages.

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Acknowledgements

We acknowledge fruitful discussions with A. V. Kimel, J. Sinova, J. Wunderlich, J. Fernández-Rossier and A. H. MacDonald, and support from the European Union European Research Council (ERC) Advanced Grant No. 268066 and FP7-215368 SemiSpinNet, from the Ministry of Education of the Czech Republic Grants No. LC510 and MSM0021620834, from the Grant Agency of the Czech Republic Grant No. 202/09/H041 and P204/12/0853, from the Charles University in Prague Grant No. SVV-2012-265306 and 443011, and from the Academy of Sciences of the Czech Republic No. AV0Z10100521 and Preamium Academiae.

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Authors and Affiliations

  1. Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech Republic

    P. Němec, E. Rozkotová, N. Tesařová, F. Trojánek & P. Malý

  2. Hitachi Cambridge Laboratory, Cambridge CB3 0HE, UK

    E. De Ranieri

  3. Institute of Physics ASCR, v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic

    K. Olejník, J. Zemen, V. Novák, M. Cukr & T. Jungwirth

  4. School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK

    J. Zemen & T. Jungwirth

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  1. P. Němec
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Contributions

Sample preparation: V.N., M.C., E.R. and E.D.R.; experiments and data analysis: E.R., N.T., P.N., P.M., K.O and T.J.; data modelling: P.N. and F.T.; theory: J.Z. and T.J.; writing: T.J. and P.N.; project planning: P.N. and T.J.

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Correspondence to P. Němec.

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The authors declare no competing financial interests.

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Němec, P., Rozkotová, E., Tesařová, N. et al. Experimental observation of the optical spin transfer torque. Nature Phys 8, 411–415 (2012). https://doi.org/10.1038/nphys2279

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