Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio

The Effect of Surfactants on Equilibrium Wetting

Contact angles B0 of aqueous solutions contacting with hydrophilic and hydrophobic surfaces were studied as affected by various surfactants (alcohols, fatty acids, soaps) under conditions close to thermodynamic equilibrium (in the atmosphere saturated with the solution vapour). The conditions of transitions from limited wetting (Bo > 0) to complete wetting, i.e. spontaneous spreading were also studied. The effect of surfactants adsorption at the solid gas interface was estimated from the isotherms of wetting tension W = cr1g Cos B0 (cr1g is the surface tension of the solution) on the basis of equation describing W as a function of concentration. It is shown that adsorption of surfactants at the solid-gas interface markedly affects wetting of hydrophilic materials. For hydrophobic materials the effect is primarily due to adsorption of surfactants at the solid- solution and solution-gas interfaces. It was found that equilibrium wetting is affected by the type of adsorption at the solid surface (physical or chemical adsorption). The influence of hydrocarbon chain length in homological series of alcohols and fatty acids on equilibrium contact angles and on transition to spontaneous spreading was studied as well

ON THE RESTORATION OF THE KINEMATIC ACCURACY OF LARGE-SIZE ROTARY-DRIVE DEVICE LONG TIME ABANDONED

Restoration of the rotary-drive device after a long non-use is an important strategic task, and the search for a way to restore it is an urgent task of the study. Previously it was found that the long-term non-use of the rotary-drive device led to a deterioration in the kinematic accuracy of its gearboxes. This article discusses possible options for restoring the kinematic accuracy of gearboxes of the rotary-drive device by increasing the metal or introducing into the control system an electromechanical device for selecting the backlash. It is shown that the restoration of the geometry of gears, as well as the bearing seats is possible, however, it requires the use of specialized equipment and significant costs. Ensuring the required kinematic accuracy due to the introduction of an electromechanical choice of backlash is achieved by considering the two schemes of the backlash-picker. The performed simulation of the operation of the drive system with an electromechanical choice of backlash in the Simulink system showed that the use of a scheme with cross-links allows for the required kinematic accuracy without significant costs. As a result, it can be argued that the introduction of an electromechanical backlash device can restore the kinematic accuracy of the rotary-drive device to acceptable values.</jats:p