ABSTRACT
We demonstrate that the ultrafast fast dynamics of the d-f exchange interaction, between conduction band electrons and lattice spins in EuTe, can be accessed using an all-optical technique. Our results reveal, in full detail, the time evolution of the d-f exchange interaction induced by a femtosecond laser pulse. Specifically, by monitoring the time resolved dynamics of the reflectivity changes and Kerr rotation of a weak light pulse reflected from the surface of the sample, it is shown that an intense femtosecond light pulse with photon energies higher than that of the bandgap, triggers spin waves in EuTe. The laser-induced spin waves modulate the d-f exchange interaction, and cause the bandgap to oscillate with an amplitude reaching 1â meV, at frequencies up to tens of GHz. The ability to control and monitor the dynamics of the exchange energy with our all-optical technique opens up new opportunities for the manipulation of magnetism at ultrafast time-scales.
Subject(s)
Electrons , Europium/chemistry , Magnetics/instrumentation , Photons , Tellurium/chemistry , Lasers, Solid-State , Optical Devices , Quantum Theory , Time FactorsABSTRACT
Stacked EuTe magnetic quantum dots (QDs) separated by SnTe spacers of increasing thickness were grown and studied using x-ray diffraction (XRD) and electron microscopy. Grazing incidence XRD indicated that the EuTe QDs are under compressive in-plane strain. Both XRD analysis and microscopy images demonstrated that the EuTe QDs are vertically aligned, as a result of the strain field produced by buried QDs. The width of the lateral error distribution in the QDs' vertical alignment from layer to layer decreases for thinner SnTe spacers, corresponding to more stressed SnTe matrices. The system can be, therefore, tuned to explore magnetic interactions between QDs. The results are discussed in the light of previous elastic strain models in anisotropic matrices from the literature.
ABSTRACT
Spectroscopy of the centrosymmetric magnetic semiconductors EuTe and EuSe reveals spin-induced optical second harmonic generation (SHG) in the band gap vicinity at 2.1-2.4 eV. The magnetic field and temperature dependence demonstrates that the SHG arises from the bulk of the materials due to a novel type of nonlinear optical susceptibility caused by the magnetic dipole contribution combined with spontaneous or induced magnetization. This spin-induced susceptibility opens access to a wide class of centrosymmetric systems by harmonics generation spectroscopy.
ABSTRACT
The absorption magnetic circular dichroism in EuTe was investigated as a function of the magnetic field at T = 2 K. In order to describe the optical spectra theoretically, we developed a model that takes into account the magnetic order of the lattice as a function of the magnetic field. The model allows us to calculate the absorption spectrum as a continuous function of the magnetic field intensity. The theory accounts for the strongly dichroic absorption seen at high fields, and for its continuous evolution towards the B = 0 spectrum, which is described by a much weaker and much broader absorption line. The drastic changes observed in the experimental spectra as a function of magnetic field are fully explained by the dependence of the Eu(2+) spin arrangement on the external magnetic field.
