57th Magnetic Materials Center Seminar
October 1, 2007, 15:30-
8th floor seminar room, Sengen
A review of my past research activities
W. H. Wang
Half-metallic ferromagnets (HFMs) have been proposed as ideal candidates for spintronic devices because they have been predicted to exhibit 100% spin polarization at the Fermi energy. From the applications point of view, a high Curie temperature for a HFM should be a key factor. For this reason, Heusler alloys have recently attracted great interest. Here, in the first part of my presentation, I shall introduce my past research activities at MPI-Germany regarding the growth, magnetism and spin polarization of single crystalline Co2MnSi Heusler alloy thin films deposited by MBE on GaAs(001) substrates [W. H. Wang et al., Phys. Rev. B. 71, 144416 (2005)].
Diluted magnetic semiconductors (DMSs), in which magnetic atoms are randomly substituted for the semiconductor atoms, are expected to be another promising candidate for spintronic devices. However, the well known DMSs, to date, display desirable magnetic properties only at temperatures well below room temperature, thereby limiting their usefulness. In the second part of my presentation, I report my recent attempts to explore the Mn-doped high temperature SiC-based DMSs when I was working at AIST-Japan. A detailed study of the growth, structural and magnetic properties of Mn-doped SiC films will be described [W. H. Wang et al., Phys. Rev. B. 75, 165323 (2007)].

Co2CrxFe1-xSi thin films: Microstructure, magnetic properties and spin polarization
S. V. Karthik
We have investigated the effect of Cr substitution for Fe on the microstructure, magnetic properties and spin polarization, P, of Co2CrxFe1-xSi bulk alloys. The spin polarization increase from P=0.57 to P=0.64 by a small substitution of Cr for Fe of x=0.02, thereafter P values are constant for high Cr concentrations up to x=0.4. . The increase in spin polarization can be attributed to both the improved L21 ordering found experimentally as well as the half metallicity predicted by ab-initio calculations in the composition range of 0≤x≤0.5. We propose the composition range of 0.02 As a next step, we optimized the sputtering conditions to obtain a single phase ordered L21 structure of the alloy in thin films on SiO2 and MgO substrate and obtained the spin polarization of these thin films to be P = 0.69 and P = 0.66 respectively using PCAR method. Also, the magnetic properties of the magnetic tunnel junctions using this alloy as the ferromagnetic electrode shall be presented.


W. Li
The coercivities of sintered NdFeB magnets are strongly connected with the microstructure. It has been proved that post sintering heat treatment is one of the most effective method to increase the coercivity of the sintered NdFeB magnet. Cu is very helpful to increase the coercivity. A lot of investigations have been performed on the effect of Cu addition, but usually they have been carried out on the model specimen with high level of Cu.In commercialized alloys, the Cu content is usually very low. here we studied the alloys with very low level of Cu. In my presentation I will report our study on the microstructure of sintered NdFeB magnets with and without optimal anealing by employing SEM and TEM. The investigation has been focused on grain boundaries, interfaces and intergranular phases.