Microstructure of soft magnetic FeCo–O(–Zr) films with high saturation magnetization

Abstract The effect of microstructure on the soft magnetic properties of (Fe 0.65 Co 0.35 ) 100− x − y Zr x O y (0⩽ x ⩽4, 0⩽ y ⩽14) films has been studied using X-ray diffraction analysis, conventional and high-resolution transmission electron microscopy, and small angle X-ray scattering techniques. The results have shown that good soft magnetic properties are associated with nanoscale grains of the α-Fe(Co) phase. The introduction of oxygen and zirconium to an Fe 0.65 Co 0.35 film caused refinement of the microstructure. When the concentration of oxygen and zirconium was low (⩽9 at%), oxide particles (CoFe 2 O 4 ) were embedded in α-Fe(Co) grains. A higher concentration of oxygen and zirconium changed the crystalline oxide to an amorphous oxide, resulting in the formation of smaller grains of the α-Fe(Co) phase. Annealing the Zr-free (Fe 0.65 Co 0.35 ) 99 O 1 film caused a drastic decrease in the coercivity, the reasons for which have been discussed based on the microstructural observations.