Soft Magnetic Properties and Microstructure of NiFe/FeCo/NiFe Thin Films with Large Saturation Magnetization.

The soft magnetic properties of NiFe/FeCo/NiFe sandwich films with high saturation magnetization are discussed in relation to the microstructure. Ta/NiFe/FeCo/NiFe/Ta films prepared using the UHV sputtering process show bcc-(110) preferred grain orientation with the <110> direction sharply perpendicular to the film plane in the FeCo layer. It was revealed that thin NiFe film with a thickness of only 3 nm works effectively as a seed layer of FeCo film to control the microstructure, resulting in a significant reduction of the coercivity. The best thickness of the FeCo layer in order to realize both soft magnetic properties and high saturation magnetization was found to be ∼100 nm. Film deposition in Ar + N2 plasma reduced the grain size, but did not lead to further improvement of the soft magnetic properties. The large lattice strain induced by N2 addition is likely to degrade the soft magnetic properties.