Magnetic anisotropy and stability of Fe3Ga compounds

The magnetic anisotropy energy and the stability of crystal modifications of D03 and L21 of Fe3Ga compounds are studied with the density functional theory methods. The magnetic anisotropy energy of the D03 structure is more than twice the same value for the L21 structure. The features in the electronic structure lead to the difference in the magnitude of spin-orbit interaction, explaining the found effect. The L21 structure is more thermodynamically stable in the entire range of the considered pressures. Under pressure, the considered crystal modifications of Fe3Ga lose their stability due to the appearance of imaginary frequencies in their phonon spectra.

Структурные особенности и магнитные свойства пленок Co-W

The structure and magnetic properties of thin polycrystalline Co100-xWx (0<x>30) films deposited by magnetron sputtering on glass substrates, including those containing buffer layers Ta, W and Ru, have been investigated. It was found that pure Co films are non-single-phase and contain hpc and fcc crystal modifications. Doping leads to an increase in the concentration of the fcc phase and enhance the texture (111), and subsequently to the amorphization of the films. Buffer layers had a certain influence on the depth and concentration localization of these transformations. A characteristic feature of the magnetism of Co-W films is a significant perpendicular component in the macroscopic magnetic anisotropy, which leads to a "trance critical" magnetic state. It was shown that its source was a textured fcc phase, the crystal anisotropy of which was enhanced by the doping of cobalt with tungsten.

Formation of two crystal modifications of Fe7C3−x at 5.5 GPa

The Fe–C system, which is widely used to grow commercial high-pressure–high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of `split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe–C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12−x . Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12−x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal–carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

Poly (1-butene-ran-ethylene) Monomodal Copolymers from Metallocene Catalysts: Structural and Morphological Differences with Increasing Ethylene Content

Samples of random poly(butene-ran-ethylene) copolymers produced with metallocene catalysts were studied in order to elucidate the different behaviors of this particular class of materials as a function of increasing ethylene (C2) content. The samples cooled down from the melt are semi-crystalline or amorphous and crystallize in different crystal modifications, depending on the amount of C2. Thermal analysis, X-ray diffraction, and microscopic techniques were used to follow the changes of the materials with aging time and to understand the structural and morphological behavior with the aim of highlighting possible peculiar properties, which may be of great interest in the application of such materials in the field of Hot Melt adhesives.

Atomistic modelling of entropy driven phase transitions between different crystal modifications in polymers: the case of poly(3-alkylthiophenes)

Atomistic MD simulation allows following continuously the experimentally observed transition between form I and form II poly(3-hexylthiophene) and poly(3-butylthiophene), evidencing unexpected reorganization.