33rd Magnetic Materials Center Seminar
December 11, 2006, 10:30
7th floor seminar room, Sengen
Effect of Cr addition on the spin polarization of Co2CrxFe1-xSi alloys
S. V. Karthik
We have investigated the effect of Cr substitution for Fe on the spin polarization, P, of Co2CrxFe1-xSi alloys using the point contact Andreev reflection method. A steep increase from P=0.57 to P=0.64 occurs 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 ≤ x ≤ 0.25 is most promising for ferromagnetic electrodes of magnetic tunneling junctions to achieve high tunneling magnetoresistance. As a first step, we are optimizing the sputtering conditions to obtain a single phase ordered L21 structure of the alloy in thin films for preparing the MTJs and GMR elements.

Demonstration of high spin polarization by Co2MnSn with quaternary alloying
A. Rajanikanth
Co2MnSn has a spin polarization of 0.6 which is relatively high amongst most of the ternary full-Heusler alloys, with the quaternary alloying the band structure can be changed resulting in a change in the spin polarization. We have allready demonstrated the increase in spin polarization by substituting Al for Sn, in this presentation the effect of Fe doping for Mn will be dicussed.

CIPGMR of spin valves using Co2FeAl0.5Si0.5 Heusler alloy as ferromagnetic layers
T. Furubayashi
Giant magnetoresistance (GMR) of three-layered thin films with the FM/NM/FM (FM: ferromagnetic metal, NM: non-magnetic metal) structure has been extensively investigated for both current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries. It is highly promising to use Heusler alloys, which have high spin polarization ratios for the FM layers for obtaining high MR ratio. Among a variety of Heusler alloys, Co2FeAl0.5Si0.5 (CFAS), which has the highest polarization ratio deduced from TMR, is expected to give also high GMR ratio.
In this seminar, I describe the magnetic properties and the CIPGMR of multilayered films using CFAS as a FM layer on one side with the structure, CFAS/Cu/CoFe. The results for the structure with CFAS on the both sides, CFAS/Cr/CFAS, are also presented.