It is well known that Nd Fe B magnet shows high performance as permanent magnets. It has been applied for various products such as sensors, actuators, and the motors for hybrid and electric vehicles, because of its high magnetocrystalline anisotropy and high saturation magnetization. From environmental issues, further high performance permanent magnet is needed. However, the coercivity of Nd Fe B magnets has reached only about 20 of the theoretical values. In order to understand the magnetization process of Nd Fe B alloys, the control of the grain size and the grain boundary is of importance. In this work, Nd Fe B/Nd Cu thin films and circular dot arrays with 2 mm in diameter have been prepared by using ultra high vacuum sputtering system, electron beam lithography and Ar ion etching system and their magnetic properties have been investigated. Remarkable difference of the magnetization process between the Nd Fe B thin films with and without Nd Cu additional layer was observed.
This second review on novel metal-free cationic polymerizations is directed to living cationic polymerization that proceeds via reversible activation of carbon-sulfur bonds of thioethers via degenerative chain-transfer (DT) mechanism. In a similar way to cationic RAFT polymerization in the first review, a small amount of triflic acid generates the cationic propagating species, which interchanges with the thioether-dormant species via the sulfonium intermediate stabilized by the sulfur atom, to induce living cationic polymerization via the DT mechanism. This system can similarly control the molecular weight up to 1 10 5 with narrow molecular weight distributions (Mw/Mn < 1.2) and controlled chain-end groups in cationic polymerization of vinyl ethers and p-alkoxystyrene. The thioether-dormant species is highly stable and tolerant in comparison to the dormant species thus far reported in living cationic polymerization. This makes the obtained polymers applicable for subsequent post-polymerization reactions without any significant damages on the C-S bonds.
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