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Spectral tunability of laser-induced spin dynamics in the ferromagnetic semiconductor CdCr2Se4

A. Pogrebna, S. Barsaume, R. R. Subkhangulov, A. V. Telegin, Yu. P. Sukhorukov, A. V. Chzhan, Th. Rasing, and A. V. Kimel
Phys. Rev. B 98, 214427 – Published 14 December 2018

Abstract

Here we report that femtosecond laser pulses are able to trigger oscillations of the magneto-optical Faraday rotation in the ferromagnetic semiconductor CdCr2Se4 in the presence of an applied magnetic field. The frequency of these oscillations is a linear function of the magnetic field and corresponds to the ferromagnetic resonance (FMR). Tuning the photon energy of the pump pulses we reveal two different mechanisms, which induce FMR precession in this material. In the case of pumping from the valence band deep into the conduction band (photon energy 3.1 eV), the phase of the spin oscillations is not sensitive to the polarization of the pump, but can be reversed over 180 deg by changing the polarity of the applied magnetic field. We assign these oscillations to the coherent spin precession triggered by ultrafast laser-induced heating. This mechanism requires a strong optical absorption in the material and becomes inactive if the pump photon energy is below the band gap. Tuning the photon energy in a wide range from 0.88 to 2.1 eV reveals the second mechanism of optical excitation of coherent spin oscillations with a maximum around 1.2 eV, i.e., very close to the energy of the band gap in the semiconductor. Contrary to the laser-induced heating, this excitation mechanism is pump polarization dependent, being the most efficient if the pump is circularly polarized. The phase of the spin oscillations is independent of the polarity of the applied magnetic field, but changes by 180 deg under reversing the helicity of light. We suggest that the effect can be interpreted in terms of spin transfer torque experienced by the network of the ordered Cr3+ spins as a result of excitation of electrons from the top of the p-type valence band to the bottom of the s-type conduction band. In particular, a strong spin-orbit interaction experienced by the carriers in the valence band is responsible for the coupling of the spins of the photogenerated carriers and the polarization of light. Due to strong pd- and sd-exchange interactions the spins of the photocarriers appear to be coupled to the network of ordered spins of the Cr3+ ions.

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  • Received 13 June 2018
  • Revised 12 September 2018

DOI:https://doi.org/10.1103/PhysRevB.98.214427

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied PhysicsAtomic, Molecular & Optical

Authors & Affiliations

A. Pogrebna1,*,†, S. Barsaume1,†, R. R. Subkhangulov1, A. V. Telegin2, Yu. P. Sukhorukov2, A. V. Chzhan3, Th. Rasing1, and A. V. Kimel1,4,*

  • 1Radboud University, Institute for Molecules and Materials, 6525 ED Nijmegen, The Netherlands
  • 2Miheev Institute of Metal Physics Ural Branch of Russian Academy of Sciences, 620990 Yekaterinburg, Russia
  • 3Siberian Federal University, 660041 Krasnoyarsk, Russia
  • 4Russian Technological University (MIREA), Moscow 119454, Russia

  • *a.pogrebna@science.ru.nl, a.kimel@science.ru.nl
  • A. Pogrebna and S. Barsaume contributed equally to this work.

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Issue

Vol. 98, Iss. 21 — 1 December 2018

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