Microstructure of columnar crystallites in Ni80Fe20/Cu magnetic multilayers

Abstract

We have used electron microscopy to investigate the microstructure of Ni80Fe20/Cu magnetic multilayers which were synthesized by dc magnetron sputtering. Columnar structure was found in the specimen with and without giant magnetoresistance (GMR). All the columnar crystallites (CCs) originate from the 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 microscopy study shows that the CCs are single-crystal-like with fcc structure resulting from the epitaxial growth of NiFe and Cu sublayers. Electron diffraction contrast imaging and electron energy filtered elemental mapping confirmed that multilayer nature is maintained throughout the entire NiFe/Cu film. 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 crystalline structure on the GMR related problems is discussed. The microstructure results revealed in this article provide useful information for the GMR property investigation of NiFe/Cu based metallic multilayers.