Microstructure of columnar crystallites in Ni80Fe20/Cu magnetic multilayers

We have used electron microscopy to investigate the microstructure of Ni80F e20/Cu magnetic multilayers which were synthesized by dc magnetron sputteri ng. Columnar structure was found in the specimen with and without giant mag netoresistance (GMR). All the columnar crystallites (CCs) originate from th e Fe buffer layer on silicon wafer or glass substrate and penetrate though all the multilayers up to the surface of the film. The lateral size of the CCs ranges from 10 to 30 nm. Cross-sectional high-resolution electron micro scopy study shows that the CCs are single-crystal-like with fcc structure r esulting from the epitaxial growth of NiFe and Cu sublayers. Electron diffr action contrast imaging and electron energy filtered elemental mapping conf irmed that multilayer nature is maintained throughout the entire NiFe/Cu fi lm. Grain boundaries between CCs can be the most likely place where NiFe or Cu bridging will occur. Columnar structure was also found in a Ta/NiFe/Cu/ NiFe/FeMn/Ta spin valve film. The possible influence of the columnar crysta lline structure on the GMR related problems is discussed. The microstructur e results revealed in this article provide useful information for the GMR p roperty investigation of NiFe/Cu based metallic multilayers. (C) 2000 Ameri can Institute of Physics. [S0021-8979(00)07406-5].