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 for N>4% (pp). Stress appears to have a major influence on the magnetic properties. Film stress correlated quite closely with H c. Hysteresis loops appear to indicate a stripe domain structure in which the magnetization has in-plane components which are aligned parallel, but perpendicular components which alternate up and down. Stripe domains were observed directly by magnetic force microscopy. The microstructure also changed significantly with added N. 1% (pp) N caused the strong (1 1 0) 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 nm or less) in an amorphous matrix. Transmission electron microscopy observations appear to indicate that the grain refinement and phase separation take 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.