Structure and soft magnetic properties of FeAl/FeN multilayered films with high B_S and μ

The structural and soft magnetic properties of FeAl/FeN multilayer films with high spontaneous induction B_S and permeability μ are investigated. The thickness of the FeAl layer is fixed at about 675 Å, while that of the FeN layers is varied from 135 to 675 Å. For the larger thicknesses of FeN layer the X-ray diffraction patterns contain peaks from γ'-Fe₄N and α-Fe. The peaks become narrower when the FeN layers become thicker. Atomic force microscopy reveals that the grain size is smaller for films with thinner layers of FeN. B_S is high (16 kG) and almost independent of the thickness of the FeN layer. The coercivity H_c decreases and μ increases when the FeN layer becomes thinner. When the thickness of the FeN layer is 135 Å, the coercivity is low (about 1 Oe), μ is high (2000 at 13 MHz), and μ changes little from 1 to 13 MHz. These results can be understood qualitatively on the basis of an increase of μ caused by enhanced coherent rotation in small particles.