Terahertz magnetization dynamics induced by femtosecond resonant pumping of ${\mathrm{Dy}}^{3+}$ subsystem in the multisublattice antiferromagnet ${\mathrm{DyFeO}}_{3}$

Terahertz magnetization dynamics induced by femtosecond resonant pumping of ${Dy}^{3 +}$ subsystem in the multisublattice antiferromagnet ${DyFeO}_{3}$

R. V. Mikhaylovskiy, T. J. Huisman, A. I. Popov, A. K. Zvezdin, Th. Rasing, R. V. Pisarev, and A. V. Kimel

Phys. Rev. B 92, 094437 – Published 24 September 2015

Abstract

Resonant optical pumping of $f - f$ electronic transitions in the ${Dy}^{3 +}$ subsystem with femtosecond laser pulses in the multisublattice antiferromagnet ${DyFeO}_{3}$ produces a strongly pronounced effect on the induced magnetization dynamics. Analyzing the polarization and spectral properties of the emitted THz radiation, we infer that the resonant pumping magnetizes the partially ordered ${Dy}^{3 +}$ ions on a femtosecond time scale with the induced longitudinal change of the magnetization reaching almost $1 %$ . We also show that for laser photon energies close to the $f - f$ resonance of ${Dy}^{3 +}$ ions, a minimum in the efficiency of spin-wave excitation in the ${Fe}^{3 +}$ subsystem via the inverse Faraday effect is observed. This observation reveals that the resonant photo-induced magnetization in the ${Dy}^{3 +}$ subsystem and the off-resonant excitation of spin waves in the ${Fe}^{3 +}$ subsystem are intrinsically competing processes.

Received 26 January 2015
Revised 3 July 2015

DOI:https://doi.org/10.1103/PhysRevB.92.094437

Authors & Affiliations

R. V. Mikhaylovskiy¹, T. J. Huisman¹, A. I. Popov², A. K. Zvezdin^3,4,5, Th. Rasing¹, R. V. Pisarev⁶, and A. V. Kimel^1,4

¹Radboud University, Institute for Molecules and Materials, 6525 AJ Nijmegen, The Netherlands
²National Research University of Electronic Technology, 124498 Zelenograd, Russia
³Prokhorov General Physics Institute, Russian Academy of Sciences, 119991 Moscow, Russia
⁴Moscow State Technical University of Radio Engineering, Electronics, and Automation, 119454 Moscow, Russia
⁵Moscow Institute of Physics and Technology (MFTI), 141700 Moscow Region, Russia
⁶Ioffe Physical Technical Institute, 194021 St. Petersburg, Russia

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Vol. 92, Iss. 9 — 1 September 2015

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Figure 1
(a) Magnetic structure of ${DyFeO}_{3}$ in relation to the geometry of the experiment. Large and small balls represent the ${Fe}^{3 +}$ and ${Dy}^{3 +}$ ions, respectively. The ${Fe}^{3 +}$ spins are aligned along the $a$ axis, while due to the Dzyaloshinskii-Moriya interaction the spins are canted and the crystal acquires a net magnetic moment $M_{S}$ along the $c$ axis. The spins of ${Dy}^{3 +}$ are partially aligned in the direction of $M_{S}^{F e}$ due to the $d - f$ exchange interaction. (b) Particular details of the electronic structure of ${Dy}^{3 +}$ ions. (c) Temporal evolution of the electric field of the THz radiation triggered by 40 fs circularly polarized pulses of opposite helicities. $σ^{(+)}$ (filled circles) and $σ^{(-)}$ (open circles) correspond to the right- and left-handed circularly polarized pump, respectively. The temperature of the sample is $T = 50$ K. The central photon energy of the pump is $ℏ ω = 1.55$ eV. (d) Fourier-transform spectrum of the time dependence shown in (c) (filled circles). The central photon energy of the pump is $ℏ ω = 1.55$ eV. The red solid line is the calculated spectrum. (e) Fourier-transform spectrum of the THz radiation for the pump with the central photon energy $ℏ ω = 0.97$ eV. The red solid line is the calculated spectrum.
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Figure 2
(a) Temperature dependence of the peak amplitude of the THz signal triggered by the pumps with the central photon energy $ℏ ω = 1.55$ eV (filled circles) and $ℏ ω = 0.97$ eV (open circles), respectively. (b) The peak amplitude of the THz radiation as a function of the central photon energy of the pump. The solid line is the fit by a Gaussian function.
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Figure 3
The THz emission in different experimental geometries. (a) THz emission as a function of the direction of the magnetization along the $c$ axis. (b) Sensitivity of the THz emission to rotation of the sample around the $a$ axis. (c) Sensitivity of the THz emission to rotation of the sample around the $b$ axis. All measurements were conducted for the same helicity of the pump light with the wavelength 1300 nm (photon energy 0.95 eV) at room temperature. The magnetization was flipped with the reversal of the bias field polarity for the fixed orientation. While the sample was rotated, the bias magnetic field was applied along the same direction to ensure the orientation of the magnetization is fixed.
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Figure 4
(a) Temporal evolution of the electric field of the THz radiation triggered by 40 fs circularly polarized pulses of opposite helicities. $σ^{(+)}$ (filled circles) and $σ^{(-)}$ (open circles) correspond to the right- and left-handed circularly polarized pump, respectively. To focus on narrowband emission at the frequency of the antiferromagnetic resonance, the measurements have been done in a time window from 5 to 25 ps. The temperature of the sample was $T = 300$ K. (b) Fourier-transform spectrum of the time dependence shown in Fig. 3. (c) The amplitude of the helicity-dependent part at the frequency of antiferromagnetic resonance as a function of the central photon energy of the pump. The helicity-dependent part was deduced performing the measurements for two opposite helicities of the circularly polarized pump and taking the difference between them. The solid line is the Gaussian function with the central frequency and the dispersion taken from the fit in Fig. 2.
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Figure 5
Temporal profile of the population of the excited state $N (t)$ induced by the Gaussian 40 fs laser pulses at the central wavelength 1275 nm (photon energy 0.97 eV).
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Figure 6
The optical pulse propagates inside the sample with thickness $d$ and induces the transient magnetization $m$ . The magnetization follows the laser pulse and propagates with its group velocity. The intensity of the laser pulse and hence the amplitude of the transient magnetization exponentially decay along the propagation direction.
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Physical Review B

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Terahertz magnetization dynamics induced by femtosecond resonant pumping of ${Dy}^{3 +}$ subsystem in the multisublattice antiferromagnet ${DyFeO}_{3}$

R. V. Mikhaylovskiy, T. J. Huisman, A. I. Popov, A. K. Zvezdin, Th. Rasing, R. V. Pisarev, and A. V. Kimel

Phys. Rev. B 92, 094437 – Published 24 September 2015

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Physical Review B

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Terahertz magnetization dynamics induced by femtosecond resonant pumping of Dy3+ subsystem in the multisublattice antiferromagnet DyFeO3

R. V. Mikhaylovskiy, T. J. Huisman, A. I. Popov, A. K. Zvezdin, Th. Rasing, R. V. Pisarev, and A. V. Kimel

Phys. Rev. B 92, 094437 – Published 24 September 2015

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Terahertz magnetization dynamics induced by femtosecond resonant pumping of ${Dy}^{3 +}$ subsystem in the multisublattice antiferromagnet ${DyFeO}_{3}$