Terahertz emission spectroscopy of laser-induced spin dynamics in ${\mathrm{TmFeO}}_{3}$ and ${\mathrm{ErFeO}}_{3}$ orthoferrites

Terahertz emission spectroscopy of laser-induced spin dynamics in ${TmFeO}_{3}$ and ${ErFeO}_{3}$ orthoferrites

R. V. Mikhaylovskiy, E. Hendry, V. V. Kruglyak, R. V. Pisarev, Th. Rasing, and A. V. Kimel

Phys. Rev. B 90, 184405 – Published 5 November 2014

Abstract

Using the examples of laser-induced spin-reorientation phase transitions in ${TmFeO}_{3}$ and ${ErFeO}_{3}$ orthoferrites, we demonstrate that terahertz emission spectroscopy can obtain novel information about ultrafast laser-induced spin dynamics, which is not accessible by more common all-optical methods. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, terahertz emission spectroscopy enables detection of a resonance optically excited at an unexpected frequency of ∼0.3–0.35 THz. By recording how the amplitude and phase of the excited oscillations depend on temperature and applied magnetic field, we show that the unexpected mode has all the features of a spin resonance of the ${Fe}^{3 +}$ ions. We suggest that it can be assigned to transitions between the multiplet sublevels of the $^{6} A_{1}$ ground state of the ${Fe}^{+ 3}$ ions occupying rare-earth positions.

Received 22 July 2014
Revised 23 September 2014

DOI:https://doi.org/10.1103/PhysRevB.90.184405

Authors & Affiliations

R. V. Mikhaylovskiy^1,*, E. Hendry², V. V. Kruglyak², R. V. Pisarev³, Th. Rasing¹, and A. V. Kimel¹

¹Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, the Netherlands
²School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, United Kingdom
³Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia

^*R.Mikhaylovskiy@science.ru.nl

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Vol. 90, Iss. 18 — 1 November 2014

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Figure 1
(a) The typical wave forms optically generated in the $z$ -cut ${TmFeO}_{3}$ . (b) The Fourier spectrum of the THz wave form generated in ${TmFeO}_{3}$ at 60 K. One can clearly observe three spectral peaks which we attribute to the quasi-ferromagnetic mode at 0.1 THz, the quasi-antiferromagnetic mode at 0.8 THz, and an unexpected resonance at 0.35 THz. (c) The amplitudes of the three spectral components of the THz emission spectra: the quasi-ferromagnetic mode (red circles), the unexpected mode (blue triangles), and quasi-antiferromagnetic mode (black squares) are shown as functions of temperature. Lines are guides for the eye.
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Figure 2
The spectral amplitudes of the quasi-antiferromagnetic (q-AFM) and quasi-ferromagnetic (q-FM) modes measured for two different values of the pump power W (85 and 40 mW) in the $z$ -cut ${TmFeO}_{3}$ sample are shown as functions of temperature. The lines are guides for the eye.
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Figure 3
(a) The Fourier spectrum of the THz wave form generated in the $x$ -cut ${ErFeO}_{3}$ at 55 K. Three spectral lines are distinguishable: the quasi-ferromagnetic mode at 0.15 THz, the unexpected peak at 0.3 THz, and the quasi-antiferromagnetic mode at 0.75 THz. (b) The amplitudes of the three spectral components of the THz emission spectra—the quasi-ferromagnetic mode (red circles), the unexpected mode (blue triangles), and the quasi-antiferromagnetic mode (black squares) are shown as functions of temperature. Lines are guides for the eye.
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Figure 4
(a) The THz wave forms generated in the $x$ -cut ${ErFeO}_{3}$ for opposite orientation of the magnetization along the $z$ axis. (b) The THz wave forms generated in the $x$ -cut ${ErFeO}_{3}$ for opposite helicities of the circularly polarized pump.
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Figure 5
(a) The motion of the iron sublattice magnetization and the magnetization of the impurities (exaggerated for clarity) due to the laser-induced spin reorientation in the $x$ -cut sample. The initial changes of the normal magnetization and the magnetization of the impurities are opposite. (b) The electric field generated in the $x$ -cut ${ErFeO}_{3}$ sample at 55 K is shown along with its components arising from the quasi-ferromagnetic mode (q-FM) and the impurity modes. These contributions have opposite initial phases at a certain time delay just after the laser excitation as shown by a dashed vertical line.
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Figure 6
Loss functions of the $z$ -cut ${TmFeO}_{3}$ at different temperatures measured for the incident THz electric field parallel to the $x$ axis (symbols) are shown together with the theoretical function.
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Physical Review B

covering condensed matter and materials physics

Terahertz emission spectroscopy of laser-induced spin dynamics in ${TmFeO}_{3}$ and ${ErFeO}_{3}$ orthoferrites

R. V. Mikhaylovskiy, E. Hendry, V. V. Kruglyak, R. V. Pisarev, Th. Rasing, and A. V. Kimel

Phys. Rev. B 90, 184405 – Published 5 November 2014

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Physical Review B

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Terahertz emission spectroscopy of laser-induced spin dynamics in TmFeO3 and ErFeO3 orthoferrites

R. V. Mikhaylovskiy, E. Hendry, V. V. Kruglyak, R. V. Pisarev, Th. Rasing, and A. V. Kimel

Phys. Rev. B 90, 184405 – Published 5 November 2014

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Terahertz emission spectroscopy of laser-induced spin dynamics in ${TmFeO}_{3}$ and ${ErFeO}_{3}$ orthoferrites