Ultrafast heating-induced magnetization switching in ferrimagnets.

We study theoretically the light-induced magnetization switching in a binary ferrimagnet of the type [Formula: see text], randomly occupied by two different species of magnetic ions. The localized spins are coupled with spins of itinerant electrons via s-d exchange interaction. Model parameters are chosen so that to achieve similarity between magnetic characteristics of the model and those of ferrimagnetic rare-earth-transition metal GdFeCo alloys. The switching is triggered by heating of the itinerant electrons by a laser pulse. The spin dynamics is governed by the cooling of itinerant electrons, exchange scattering, induced by the s-d exchange interaction and spin-lattice relaxation of the itinerant spins with a characteristic time [Formula: see text]. The dynamics of the localized and itinerant spins is described by coupled rate equations. The main conclusion of this study is that the switching occurs only in a certain temperature range depending on [Formula: see text]. For long [Formula: see text] the switching occurs only below the magnetisation compensation temperature T K. For physically reasonable values of [Formula: see text] this temperature range extends from 0 K to [Formula: see text], where [Formula: see text] is slightly higher than the compensation temperature T K. With further decrease of [Formula: see text] this temperature range shifts to temperatures higher than T K.

Coherence-mediated laser control of exciton and trion spins in CdTe/CdMgTe quantum wells studied by the magneto-optical Kerr effect.

Two temporally non-overlapping linearly cross-polarized 140 fs laser pulses are shown to control the spin polarization in a three-level system. Simultaneous excitation of the two excited states triggers quantum beatings originating from the interference of the wavefunctions corresponding to different spin sublevels of the states. Although the beatings are not seen in the spin densities of the excited states they are clearly observed in the magneto-optical Kerr effect. An analytical expression for the description of the beatings is obtained. Experimental results are in good agreement with theoretical predictions and demonstrate the control of beatings with attosecond resolution.

Impulsive generation of coherent magnons by linearly polarized light in the easy-plane antiferromagnet FeBO3.

Polarization-dependent excitation of coherent spin precession by 150 fs linearly polarized laser pulses is observed in the easy-plane antiferromagnet FeBO3. We show that the mechanism of excitation is impulsive stimulated Raman scattering. This process is shown to be determined not only by the magneto-optical constants of the material, but also by the properties of the spin precession itself. Though carrying no angular momentum, the linearly polarized laser pulses act on the spins as effective fields that can be considered as an ultrafast inverse Cotton-Mouton effect.

Ultrafast optical pumping of spin and orbital polarizations in the antiferromagnetic Mott insulators R(2)CuO(4).

We demonstrate that optical pumping by circularly polarized light at the charge-transfer transition can induce spin and orbital polarizations in the strongly correlated Mott insulators R(2)CuO(4) (R=Pr, Nd, Sm) providing a means of ultrafast nonlinear manipulation of spin states on time scales of less than 150 fs. We propose a model which includes both orbital- and spin-related processes possessing different spectral and temporal properties. This allows us to model the optical response of antiferromagnetic Mott insulators to circularly polarized light and estimate the spin relaxation time as tau(s) approximately 30-50 fs.

[Electrophoretic properties of a population of Escherichia coli cells studied by microelectrophoresis]. / Issledovanie élektroforeticheskikh svoistv populiatsii kletok Escherichia coli metodom mikroélektroforeza.

The technique of microelectrophoresis was used to measure the rate of E. coli cell motility under the action of a constant electric field, and the electrokinetic potential (xi-potential) was calculated from the experimental data. As was shown by analysing the results for a sample from 100 cells, the property varied within a wide range which exceeded several times the error of a single measurement. This variation was associated with the different electrosurface properties of microbial cell groups and is characteristic of a cell population. The empirical distribution of the parameter was shown to be consistent with the normal law. The results of determining the electrokinetic potential may statistically be processed with a computer, and the profile of an experimental curve will characterize the physico-chemical state of cells.

[Studies on the coil-globule transition by the Monte-Carlo method]. / Izuchenie perekhoda klubok - globula metodom Monte-Karlo.

The results of a dynamical Monte-Carlo study on the coil-globule and globule-coil transitions are presented. Self-avoiding chains of lengths N = 32 and 64 are investigated. The kinetic model included two- and three-bonds flips. The relaxation of the chain was induced by the abrupt change of the interaction between the monomers. The time evolution of the radius of gyration and the number of intramolecular contacts was obtained. It is established that the transition to the compact state occurs due to the contacts between the monomers close to each other along the chain. The results obtained are compared with the predictions of analytical theories.