The effect of nitrogen on the microstructure, stress, and magnetic properties of RF-sputtered FeSiAl(N) thin films

In a series of RF-sputtered soft FeSiAl(N) films, the partial pressure (pp) of N in the plasma was observed to have a profound effect on the magnetic properties, stress, and microstructure. 1% (pp) N caused the coercivity (H- c) to more than double. H-c peaked for 3% (pp) N, then decreased steeply fo r N > 4% (pp). Stress appears to have a major influence on the magnetic pro perties. Film stress correlated quite closely with H-c. Hysteresis loops ap pear to indicate a stripe domain structure in which the magnetization has i n-plane components which are aligned parallel, but perpendicular components which alternate up and down. Stripe domains were observed directly by magn etic force microscopy. The microstructure also changed significantly with a dded N. 1% (pp) N caused the strong (110) texture to become very weak. For > 4% (pp) N, there was a transition from textured columnar 100 nm diameter BCC grains to a mixture of randomly-oriented, equiaxed BCC nanograins (10 n m or less) in an amorphous matrix. Transmission electron microscopy observa tions appear to indicate that the grain refinement and phase separation tak e place by a decomposition process. Saturation magnetization also decreased with added N for > 4% (pp) N, indicating that one of the two phases has a lower M-s value. (C) 2001 Elsevier Science B.V. All rights reserved.