Multiferroic and Nanomechanical Properties of Bi1−xGdxFeO3 Polycrystalline Films (x = 0.00–0.15)

In this work, we adopted pulsed laser deposition (PLD) with a Nd:YAG laser to develop Bi1−xGdxFeO3 (BGFO) films on glass substrates. The phase composition, microstructure, ferroelectric, magnetic, and nanomechanical properties of BGFO films are studied. BGFO films with x = 0.00–0.15 were confirmed to mainly consist of the perovskite phase. The structure is transformed from rhombohedral for x = 0.00 to pseudo-cubic for x = 0.05–0.10, and an additional phase, orthorhombic, is coexisted for x = 0.15. With increasing Gd content, the microstructure and surface morphology analysis shows a gradual decrease in crystallite size and surface roughness. The hardness of 5.9–8.3 GPa, measured by nanoindentor, is mainly dominated by crystallized structure and grain size. Good ferroelectric properties are found for BGFO films with x =0.00–0.15, where the largest remanent polarization (2Pr) of 133.5 µC/cm2 is achieved for x = 0.10, related to low leakage and high BGFO(110) texture. The improved magnetic properties with the significant enhancement of saturation magnetization from 4.9 emu/cm3 for x = 0 to 23.9 emu/cm3 for x = 0.15 by Gd substitution is found and related to large magnetic moment of Gd3+ and suppressed spiral spin structure of G-type antiferromagnetism. Furthermore, we also discuss the mechanisms of leakage behavior as well as nanomechanical characterizations as a function of the Gd content.

Effect of Initial Conditions and Numerical Investigation of Instability Developed during Synthesis of TiC via Vortex Combustion at Moderate Temperatures. Model of Vortex Combustion

Despite the fact that the classical theory of combustion (CTC) operates with the simplest, elementary objects and concepts, such as: flat or slightly curved combustion fronts, elementary combustion models and potential flows. there are some problems that the CTC is only facing with a sufficiently strong curvature of the front. For example, Markstein's solution in the problem of hydrodynamic instability of a plane combustion front. In the work presented by the authors, the problem of stabilizing the titanium carbide synthesis front at moderate temperatures, which cannot be plane due to the thermo physical features of the system under consideration (Le<<1, Ze=6.03 at Тad=3300К), is similarly solved. A model of vortex combustion with a spirally curved front is proposed, the numerical analysis of which showed the stability of similar front of the TiC synthesis in the field of vortex hydrodynamic currents. The resulting solution can serve as a complete alternative to the mode of spiral spin combustion (or rather, to its branch with a low orbital speed and a low combustion temperature) of such systems, not only considered conditionally unstable in CTC, but also actually manifesting this instability during numerical calculations of the area of the existence of a spinal spot with a small radius and great curvature.

Effect of octahedron tilt on structure and magnetic properties of bismuth ferrite

Multiferroic trivalent ions doped BiFeO3 ceramics were synthesized using the rapid liquid state method. The trivalent ions (Sm3+, Gd3+, Y3+) doping causes structural distortion without changing the rhombohedral structure. Raman analysis shows that the effect of doping on E modes is greater than A1 modes, and FeO6 octahedron is regulated by ions doping. M-H hysteresis loops show A-site trivalent ions doped samples exhibit improved magnetism compared with pure BiFeO3 since the suppressed spiral spin structure. Doped samples exhibited natural resonance around 16~17 GHz due to the changes in dielectric loss caused by the tilt of the FeO6 octahedron.

A Introduction to the Classical Spiral Electrodynamics: The” Spiral-Spin”

This paper demonstrates the existence of analytical solutions of the Lorentz equation for charged particles in “uniform pilot time-varying magnetic fields". These analytical solutions represent a temporal generalization of the Larmor's orbits and are expressed through a Schwarz-Christoffel spiral mapping or in spiral coordinates. The concepts of "spiral-spin” moment and "polar-spiral" angular momentum are then presented, the existence of a subclass of solutions for which these two angular moments are conserved is demonstrated. It is also shown that under the action of the "pilot fields," there exist particular trajectories for which the charged particles have a "spiral-spin" momentum constant proportional to +1/2 (solution named "spiral-spin-up ") and -1/2 (solution named "spiral-spin-down "), respectively. The results are in full agreement with the ideas of L.DeBroglie and A. Einstein on the possible existence of pilot fields able to describe the physical reality deterministically. Finally, the solution of the Lorentz equation is discussed with the WKB (Wentzel-Kramers-Brillouin) method for a superposition of two uniform magnetic fields with the same direction, the first constant and the second time-varying.