38th Magnetic Materials Center Seminar
February 22, 2007, 9:00
7th floor seminar room, Sengen
Ideas to manipulate magnetic properties of selected alloys based on ab-initio calculations
Z. Gercsi
Last time I presented ab-initio quantum mechanical calculations to discuss the role of structural disorder on the density of states and on the magnetic properties of some selected Co-based full-Heusler alloys. These simulations with superlattice structures are useful to predict alloys and compounds with high magnetization and superior resistance of half-metal electronic structure against structural changes.
Nevertheless ab-initio calculation is also a very powerful tool to predict (or interpret) changes in the saturation magnetization (Ms) or magneto-crystalline anisotropy (Ku) due to change in the type of crystal lattice and lattice constant or due to the presence of some structural distortion. In modern material science, there are various existing techniques (such as sputtering techniques for thin films or ball milling for bulks, etc.) by which we are able to manipulate the equilibrium atomic structure of a magnetic substance.
For instance in FeCo alloys, an improvement of Ms (over 2.5T!) together with a high Ku induced by the change in the lattice parameter were recently proved both theoretically and experimentally [1]. In my talk, I will propose some new ideas correspondingly these calculations as well as some new ideas to prepare MTJs for high TMR.

[1] G. Anderson et. al. PRL 96, 0372205 (2006)

Microstructure study on HDDR and sintered NdFeB magnets
W. Li
HDDR process is a very effective method to get NdFeB magnet with fine grains. The HDDR process can be separated into several steps. And in each step there are some parameters can be adjusted. Therefore in HDDR process there are many variables that can influence the process and thus the performance of the HDDR magnets. In this presentation I will report our study in the microstructure of HDDR samples treated under different disproportionatin g process.
I will also report our study on the microstructure of sintered NdFeB magnets with and without Cu addition. Previously, we have studied the distribution of Cu in the NdFeB magnet by TEM and 3DAP, and recently we have been focused on the distribution of Nd-rich phase in sintered NdFeB magnets with and without Cu addition.