Тип публикации: статья из журнала
Год издания: 2018
Идентификатор DOI: 10.1103/PhysRevB.98.214427
Ключевые слова: Differential scanning calorimetry, Germanium oxides, Indium, Solid state reactions, Specific heat, Thermodynamic properties, Enthalpy increments, Entropy changes, Germanate, High temperature, Molar heat capacities, Polycrystalline, Reduced Gibbs energies
Аннотация: 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 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 pd- and sd-exchange interactions the spins of the photocarriers appear to be coupled to the network of ordered spins of the Cr-3(+) ions.
Журнал: PHYSICAL REVIEW B
Выпуск журнала: Vol. 98, Is. 21
Номера страниц: 214427
ISSN журнала: 24699950
Место издания: COLLEGE PK
Издатель: AMER PHYSICAL SOC
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