47th Magnetic Materials Center Seminar
June 8, 2007, 10:30
7th floor seminar room, Sengen
My report on the progress of FeSiB thin films and other related alloys
Z. Gercsi
The highest TMR effect up to date was measured in CoFeB thin films with coherent tunneling mechanism. As it is known, the TMR effect depends not only on the inner spin polarization of the magnetic layer but also on various other parameters such as: exchange bias (111 orientation of IrMn), roughness of the junction, structure of the magnetic layer (amorphous or partly nanocrystallized), etc. The optimization of these properties requires extensive seeks for suitable seed layers, sputtering conditions, and pre/post annealing treatments. In my talk, I will report my current efforts to develop exchange bias in FeSiB based thin films for coherent tunneling, together with preliminary TMR results.
Furthermore, results of theoretical calculations on selected full- and also half-Heusler alloys will be discussed as well.

Microstructure study on NdFeB magnet with small grain size
W. Li
To obtain magnets with high values of coercivity it is necessary to have a small average grain size of the main phase Nd2Fe14B. By decreasing the size of the powders for sintering process one can decrease the grain size of the Nd2Fe14B phase and increase the coercivity of the magnet. while there is a critical grain size below which the coercivity can not be increased by decreasing the grain size. in this presentation i will report our study in the microstruture of sintered NdFeB magnets with very fine grain size. Focuses have been put on the oxides due to decreased grain size.

NdFeB Permanent Magnets (Approaches to High coercivity !!!)
K. Suresh
High coercivity is a primary requisite for hard magnetic material applications (permanent magnet). In laboratory as well as industrially realized coercivity of these materials are falling far less than, 20 to 40 %, the theoretically predicted value. This discrepancy is due to various microstructural factors such as crystal defects, degree of misalignment of grains, secondary phases (usually soft magnetic), precipitates and inter grain interactions (exchange coupling) in sintered magnets. Advent of new processing techniques and characterization tools are opened doors to tailor the desirable microstructure to obtain enhanced properties.
High coercive Nd2Fe14B magnetic materials can be realized by its nano-structured grains which are isolated by uniformly distributed nonmagnetic grain boundary phase. This type of tailored microstructure has been obtained in thin films and spark plasma sintering of magnetic field compacted HDDR, melt-spun flakes and mechanically milled powders. In this presentation, I would show preliminary results of Nd2Fe14B magnets prepared using thin film technique and spark plasma sintered HDDR bulk materials.