Magnetic and structural investigations on substituted Pr2Co17-xTx systems (T= Fe, Mn, Cr, Cu and Al)

Magnetic and structural characteristics of Pr₂Co₁₇-based ternaries, in which Co is partly replaced by other transition elements, namely Fe, Mn, Cr, Cu and Al, have been investigated. The objective of the work was to explore the possibility of enhancing the anisotropy of Pr₂Co₁₇ to the point that it would be useful for permanent magnet fabrication. X-ray diffraction indicates that all the systems studied occur in the rhombohedral Th₂Zn₁₇ structure. The cell constants increase as Fe, Mn, etc., are introduced in the system, which indicates that substitution occurs in the Co sublattice. The Curie temperatures, T_c, decrease monotonically with increasing x in the order Fe < Cu < Mn < Al < Cr. The saturation magnetization, M_s, increases with increasing x for the Fe system with x 8. For x #62; 8 in the Pr₂Co_17-xFe_x system and in all other ternary systems st died, M_s decreases with x, the magnitude of the effect being in the order Cr #62; Al #62; Mn #62; Cu. The rate of decrease is larger than that expected as a simple dilution except for the systems containing Cu. Significant modification of the anisotropy characteristics of Pr₂Co₁₇ is observed upon substitution. The planar anisotropy of Pr₂Co₁₇ becomes uniaxial with Fe (x 4) and Mn (x 2) substitutions. With Cr and Al substitutions, the plane-seeking tendency of Pr₂Co₁₇ is significantly weakened.     

Magnetostrictive strain and thermal expansion in NdCo5 in the spin orientation temperature region

Magnetostrictive strain and thermal expansion measurements in an oriented assembly of NdCo₅ particles along the c-axis were carried out between 77 and 330 K. The measurement strains in the c-derection and transverse to the c-direction exhibited anomalous behavior at 285 and 245 K, which are assoiciated with the spin reorientation process in this temperature range. The estimated magnetostrictive energy $\text{1}\text{2}\text{E(λ}{}_{\mathrm{c}}\text{- λ⊥}{}_{\mathrm{c}}\text{)}{}^2$ is comparable to the anisotropy energy at 285 K. There is also a pronouced anomaly in ther thermal expansion in the spin reorientation temperature region.     

Friction,adhesion and wear durability of an ultra-thin perfluoropolyether-coated 3-glycidoxypropyltrimethoxy silane self-assembled monolayer on a Si surface

The tribological properties, such as coefficient of friction, adhesion and wear durability of an ultra-thin (<10?nm) dual-layer film on a silicon surface were investigated. The dual-layer film was prepared by dip-coating perfluoropolyether (PFPE), a liquid polymer lubricant, as the top layer onto a 3-glycidoxypropyltrimethoxy silane self-assembled monolayer (epoxy SAM)-coated Si substrate. PFPE contains hydroxyl groups at both ends of its backbone chain, while the SAM surface contains epoxy groups, which terminate at the surface. A combination of tests involving contact angle measurements, ellipsometry, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) was used to study the physical and chemical properties of the film. The coefficient of friction and wear durability of the film were investigated using a ball-on-disk tribometer (4?mm diameter Si₃N₄ ball as the counterface at a nominal contact pressure of ～330?MPa). AFM was used to investigate the adhesion forces between a sharp Si₃N₄ tip and the film. This dual-layer film had a very low coefficient of friction, adhesion and wear when compared to epoxy SAM-coated Si only or bare Si surface. The reasons for the improved tribological performance are explained in terms of the lubrication characteristics of PFPE molecules, low surface energy of PFPE, covalent bonding between PFPE and epoxy SAM coupled with reduced mobile PFPE. The low adhesion forces coupled with high wear durability show that the film has applications as a wear resistant and anti-stiction film for microcomponents made from Si.     

Design and synthesis of spirobiisoxazoline dibenzoquinone derivatives via [3 + 2] double 1,3-dipolar cycloaddition reaction

“A series of novel spirobiisoxazoline dibenzoquinone derivatives were synthesized starting from 2,5-dimethoxybenzaldehyde in a six-step synthetic sequence”. The key step [3?+?2] double 1,3-dipolar cycloaddition of oxime chloride with allenoate was performed under mild reaction conditions using sodium carbonate at ambient temperature. This is the first innovative synthesis of Spirobiisoxazoline Dibenzoquinone system where quinone ring is alkylated to isoxazoline moiety.