7th Metallic Nanostructure Group Seminar
January 26, 2006, 9:00 am
7th floor seminar room, Sengen
Structural change in supercooled liquid region of metallic glass
T. Ohkubo
Tanner et al. reported a double Tg like feature in DSC profile of Zr36Ti24Be40 metallic glass. Kumar et al. suggested that this inflection point in supercooled liquid region is due to overlapping with small exothermic peak which is related with evolution of SRO. In order to understand this inflection point precisely, we analyzed the structural change in supercooled liquid region of metallic glass by molecular dynamics simulation. From the calculated DSC profile and changes of Voronoi polyhedra, we found that the inflection point is due to volume decreasing which is caused by formation of TSRO toward to the crystalline phase, and also the crystallization is suppressed by increasing of additional 2nd and 3rd elements since the variety of configuration is increased.

Coercivity of permanent magnets
K. Hono
Nd2Fe14B based sintered magnets are most widely used permanent magnetic material, but its coercivity is only 20% of the anisotropy field. To increase coercivity, Dy is replaced for Nd to increase the anisotropy at the grain boundary. However, since the spin orientation of Dy is opposite to that of Nd, Dy replacement results in reduction of remanence. In this talk, I will give a textbook type overview on the coercivity of permanent magnets and show typical examples for nucleation and pinning type coercivity. Then, I will show recent examples of extremely high coercivity reported from magnetically isolated FePt nanoparticles, whose coercivity is larger than 90% of the anisotropy field. This suggests that if we are able to produce ideal microstructure, it is possible to enhance the coercivity at least 50% of the anisotropy. The coercivity expected from this is larger than 35 kOe for Nd2Fe14B. I will propose several experimental studies to enhance coercivity of Nd2Fe14B based sintered magnets.