Spectral dependence of the photoconductance in CdCr2Se4: Band and donor level splitting due to ferromagnetic ordering

Stoyanov, S. G.; Iliev, M. N.; Stoyanova, S.

doi:10.1016/0038-1098(76)90985-6

Cited by 19 publications

(2 citation statements)

References 9 publications

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“…8(a)]. Regarding such a spectral dependence with a maximum corresponding to the maximum in the absorption spectrum [35], we suggest that the mechanism of excitation of spin precession can be explained by optical spin transfer torque, similarly to Ref. [19].…”

Section: B Pump Photon Energies Below the Band Gapsupporting

confidence: 53%

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

et al. 2018

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Here we report that femtosecond laser pulses are able to trigger oscillations of the magneto-optical Faraday rotation in the ferromagnetic semiconductor CdCr 2 Se 4 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 Cr 3+ 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 pdand sd-exchange interactions the spins of the photocarriers appear to be coupled to the network of ordered spins of the Cr 3+ ions.

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Section: B Pump Photon Energies Below the Band Gapsupporting

confidence: 53%

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

et al. 2018

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“…Therefore we cannot expect an accurate description of the observed phenomena. A preliminary discussion on the problem can be found in [9]. The TR structure above 2.1 eV obviously arises from direct band-to-band transitions.…”

Section: Discussionmentioning

confidence: 99%

Thermoreflectance of CdCr₂S₄ near the Curie Point

Iliev

Pink

1979

Physica Status Solidi (b)

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The thermoreflectance (TR) spectrum of the ferromagnetic semiconductor CdCr,S, (T, = 86 K)is measured between 24 and 330 K at photon energies ranging from 1.5 t o 3.2 eV. A magneticorder-induced band splitting associated with the earlier observed anomalous C-band (Ec = = 1.87 eV a t 4.2 K) is found below the Curie-Weiss temperature as well as a n additional "red shifting" structure a t higher photon energies. The results support the assumption of a strong coupling between the electron and spin subsystems in ferromagnetic spinels. The mechanism of the spin-dependent electronic processes seems to be more complex than predicted by the simplest models.~CCJIeAOBaH CIIeKTp TepRlOOTpameHHfl (TO)

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Photoinduced infra‐red optical absorption in CdCr₂Se₄ magnetic semconductor

Hlı́dek

Zvára

Prosser

1977

Physica Status Solidi (b)

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Magnetic semiconductors exhibit many interesting effects due to mutual interrelations of electric, optical, and magnetic properties. A few photoinduced effects in the magnetic semiconductor CdCr Se have been reported so far: photoconductivity /1 to 3 / , change of the high frequency magnetic permeability under illumination /4 to 6 / , change of magnetic hysteresis loops /7/, effect of light on the ferromagnetic resonance and on magnetostatic modes, and finally change of the spectral dependence of photoconductivity under additional illumination /8/. These effects a r e induced by photons with energies in the region of the absorption edge, more precisely in the region of the absorption band which emerges from the absorption edge with increasing magnetic ordering of the sample /9/. This "red shiftingv7 absorption band reveals pronounced polarization properties / l o / . This short note deals with the optical absorption structures within the spectral range 0 . 1 to 1 . 1 eV induced by an additional illumination with photon energies in the region of the mentioned "red shifting" band. 4Single crystals of CdCr Se were grown from the melt of anhydrous CdC12 and 2 4 they were found to be compensated p-type samples. The specimens for measurements were prepared in the form of plates with thicknesses 0 . 1 to 0 . 5 mm by grinding and mechanical polishing.The optical absorption measurements were .performed with a Carl Zeiss SPM 2 monochromator with LiF and NaCl prisms in the respective spectral regions. The excitation spectra were measured by another SPM 2 monochromator with a glass prism. The circular polarization of beams in the region of photon energies 0 . 4 t o 1 . 4 eV was obtained by a polarizer coupled with a calibrated Babinet-Soleil compensator. The beam used for absorption measurements ("probing beam") was commonly chopped at the frequency 290 Hz in the spectral range 0 . 4 to 1 . 2 eV (PbS photodetector). Only measurements of the dependence of the excitation spectra on the

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Spectral dependence of the photoconductance in CdCr2Se4: Band and donor level splitting due to ferromagnetic ordering

Cited by 19 publications

References 9 publications

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

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

Thermoreflectance of CdCr₂S₄ near the Curie Point

Photoinduced infra‐red optical absorption in CdCr₂Se₄ magnetic semconductor

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Spectral dependence of the photoconductance in CdCr2Se4: Band and donor level splitting due to ferromagnetic ordering

Cited by 19 publications

References 9 publications

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

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

Thermoreflectance of CdCr2S4 near the Curie Point

Photoinduced infra‐red optical absorption in CdCr2Se4 magnetic semconductor

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Product

Resources

About

Thermoreflectance of CdCr₂S₄ near the Curie Point

Photoinduced infra‐red optical absorption in CdCr₂Se₄ magnetic semconductor