67th Magnetic Materials Center Seminar
February 14, 2008, 9:00-
8th floor middle seminar room, Sengen
Optimization of multilayer thin films for MTJs using MgO buffer layer.
S. V. Karthik
Co2CrxFe1-xSi (CCFS) Heusler alloys with 0 < x < 0.1 has been proposed as promising material for TMR applications owing to their high spin polarization (P=0.65) measured by PCAR technique. We prepared the multilayer MTJs deposited on amorphous SiO2 (a-SiO2) and MgO 001 single crystalline substrates. The interfaces of a-SiO2 / CCFS, MgO / CCFS and CCFS free layer / MgO barrier was found to be quite rough due to the improper growth conditions. This has fuelled the need to add a buffer layer and other optimization conditions to improve the surface / interface quality. In this presentation, we fabricated MTJs using MgO buffer layer and studied their surface morphology and nano-microstructure.

Magnetic tunnel junctions with full-Heusler Co2FeAl0.5Si0.5 electrodes
H. Sukegawa
We are focusing on a Co2FeAl0.5Si0.5 (CFAS) alloy as a promising candidate for a half-metal. Magnetic tunnel junctions with the structures of full-epitaxial CFAS/MgO/CFAS on MgO buffer layers were prepared on MgO (001) substrates using a dc magnetron sputtering. We optimized in-situ annealing temperature and time after deposition of CFAS layers in order to achieve higher L21 ordering and higher tunnel magnetoresistance (TMR) ratio. Additionally, we introduced a wedge-shaped MgO barrier using a linear shutter. This provides MTJs with various barrier thicknesses in a single deposition process. In the presentation, I will show and discuss TMR properties at both room and low temperature.