Influence of interstitial nitrogen on the structural and magnetic properties of FeCoV/TiNx multilayers

FeCoV/TiNx and FeCoV/Ti multilayers having t(FeCoV)=30-700 Angstrom prepared by dc magnetron sputtering are investigated by x-ray diffraction, stress, and magnetization measurements. The x-ray diffraction data of the FeCoV/TiNx system show the presence of interstitial N atoms in the FeCoV layers due to reactive sputtering of Ti with nitrogen. The interstitial N causes an expansion of the FeCoV lattice in FeCoV/TiNx for small t(FeCoV). However, for the samples with large t(FeCoV), no lattice expansion is observed. In addition to the lattice expansion caused by the intake of N atoms, a change in the crystalline texture of FeCoV layers is also observed as indicated by the enhancement of the FeCoV(200) peaks. The magnetic hysteresis measurements on the samples show that the easy direction of magnetization lies in the plane of the layers. They further show that there are easy and hard axes of magnetization within the plane of the FeCoV layers. The stress anisotropy present in the plane of the samples induces a magnetic anisotropy through magnetostrictive effects leading to the formation of the in- plane easy axis. The hysteresis and stress measurements carried out on these samples clearly show the influence of N on the in-plane magnetic anisotropy. The magnetoelastic energy in the case of the FeCoV/TiNx system, calculated from the stress data and from the magnetization measurements as a function of t(FeCoV) is found to agree over a large range of thickness, whereas the curves deviate significantly for small layer thickness. This deviation may be due to the role of the FeCoVNx phase. Hysteresis measurements also show that the remanence is about 95% for all the samples of the FeCoV/TiNx system. In contrast, the coercivity increases linearly with increasing t(FeCoV) in this system. The coercivity of the FeCoV/Ti system is larger and increases more rapidly with t(FeCoV), as compared with the FeCoV/TiNx system. This behavior is attributed to a smaller grain size in the FeCoV/TiNx system due to the reactive sputtering of the Ti layers. However, there is no significant influence of N on the saturation magnetization of both systems. (C) 200