Measurement of the Hall effect at nanoscale with three probes.

The Hall effect and its varieties such as quantum, anomalous, and spin Hall effects provide indispensable tools for the characterization of electronic and magnetic properties of materials, metrology, and spintronics. The conventional four-probe Hall configuration is generally not amenable to measurements at nanoscale due to current shunting by the Hall electrodes. We demonstrate that Hall measurements on the nanoscale can be facilitated by the three-probe Hall configuration that avoids the shunting problem. We illustrate the efficiency of the proposed approach with anomalous Hall effect-based measurements of individual activation events during domain wall motion in magnetic films with perpendicular anisotropy.

Hydrodynamic instability in a magnetically driven suspension of paramagnetic red blood cells.

We investigate the magnetically driven motion in suspensions of paramagnetic particles. Our object is diluted deoxygenated whole blood with paramagnetic red blood cells (RBCs). We use direct observations in a closed vertical Hele-Shaw channel, and a well-defined magnetic force field applied horizontally in the channel plane. At very low cell concentrations, we register single-particle motion mode, track individual cells and determine their hydrodynamic and magnetic characteristics. Above 0.2 volume percent concentration, we observe local swirls and a global transient quasi-periodic vortex structure, intensifying with increasing cell concentration, but surprisingly this does not influence the time and purity of the magnetic extraction of RBCs. Our observations shed light on the behavioral complexity of magnetically driven submagnetic suspensions, an important issue for the emerging microfluidic technology of direct magnetic cell separation and intriguing for the mechanics of particulate soft matter.

Spin-current nano-oscillator based on nonlocal spin injection.

Nonlocal spin injection has been recognized as an efficient mechanism for creation of pure spin currents not tied to the electrical charge transfer. Here we demonstrate experimentally that it can induce coherent magnetization dynamics, which can be utilized for the implementation of novel microwave nano-sources for spintronic and magnonic applications. We show that such sources exhibit a small oscillation linewidth and are tunable over a wide frequency range by the static magnetic field. Spatially resolved measurements of the dynamical magnetization indicate a relatively large oscillation area, resulting in a high stability of the oscillation with respect to thermal fluctuations. We propose a simple quasilinear dynamical model that reproduces well the oscillation characteristics.

Synchronization of spin Hall nano-oscillators to external microwave signals.

Recently, a novel type of spin-torque nano-oscillators driven by pure spin current generated via the spin Hall effect was demonstrated. Here we report the study of the effects of external microwave signals on these oscillators. Our results show that they can be efficiently synchronized by applying a microwave signal at approximately twice the frequency of the auto-oscillation, which opens additional possibilities for the development of novel spintronic devices. We find that the synchronization exhibits a threshold determined by magnetic fluctuations pumped above their thermal level by the spin current, and is significantly influenced by the nonlinear self-localized nature of the auto-oscillatory mode.

Magnetophoretic trajectory tracking magnetometry: a new technique for assessing magnetic properties of submagnetic microparticles and cells.

We develop a new approach for assessing magnetic properties of submagnetic microparticles and cells, magnetophoretic trajectory tracking magnetometry (MTTM), that employs recording of long 2D trajectories of particle motion in a slot fluid channel caused by the action of crossed gravitational and magnetic forces. The studies are focused on the development of theoretical backgrounds of the method and evaluation of its uncertainty caused by the mutual hydrodynamic entrainment of moving particles. Computerized equipment implementing MTTM technique is described and its performance is illustrated. According to our studies, the new technique can serve a reliable experimental method with analytical qualities.

[Taking account of macromolecule conformation dynamics in the analysis of luminescent probe signals].

A mathematical model of electron excitation energy transport between molecular probes sorbed on the polymeric chain in solution was proposed. The kinetics of the process was described in terms of the conception of stochastic changes in macromolecule conformation. The results of computer simulation and the analytical expressions obtained in the framework of the perturbation theory for the cases of low transfer rate and/or fast conformation motion of the macrochain are presented. A channel of nonlinear deactivation as a result of binary annihilation of closely-spaced excited centers was considered. Expressions for the effective rate of mutual quenching and delayed annihilation fluorescence of the probe were obtained. Time dependencies of typical luminescent signals and parameteric curves of relative fluorescence quantum yield are presented.