Structure and magnetic properties of columnar Fe-N thin films deposited by direct current magnetron sputtering
(1. College of Physics, Beihua University, Jilin 132021, China;
2. Department of Materials Science, Key Laboratory of Automobile Materials of Ministry of Education,
Jilin University, Changchun 130012, China;
3. Yancheng Institute of Technology, Yancheng 224003, China)
2. Department of Materials Science, Key Laboratory of Automobile Materials of Ministry of Education,
Jilin University, Changchun 130012, China;
3. Yancheng Institute of Technology, Yancheng 224003, China)
Abstract: Columnar Fe-N thin films with thickness ranging from 30 to 150 nm were deposited by direct current magnetron sputtering using an Ar/N2 gas mixture (V(N2)/V(N2+Ar)=5%) on corning glass substrates. The structure, surface morphology and magnetic properties were investigated using X-ray diffractometry(XRD), scanning electron microscopy, atomic force microscopy, transmission electron microscopy(TEM) and superconducting quantum interference magnetometry. XRD investigation shows that Fe-N films exhibit amorphous-like structures; however, TEM measurements indicate the synthesis of mixture phases of α-Fe+ζ-Fe2N+ε-Fe3N in these films. The magnetic anisotropy and coercivity of Fe-N thin films exhibit strong dependence on the film growth behavior and surface morphology. With increasing the height of Fe-N films with column structures, the coercivity increases from 7.96 kA/m to 22.28 kA/m in the direction parallel to the film surface. In perpendicular direction the coercivity only increases slightly from 39.79 kA/m to 43.77 kA/m. However, the values of anisotropy field increase from 0.79×106 to 1.44×106 A/m, which is mainly attributed to the shape anisotropy of elongated columns due to the fact that the difference of magneto-crystalline anisotropy among these Fe-N films is small. The saturation magnetizations of Fe-N films vary with increasing film thickness from 23.5 to 85.1 A∙m2/kg.
Key words: Fe-N thin film; coercivity; magnetic anisotropy; saturation magnetization