Improved magnetic anisotropy of Co-based multilayer film with nitrogen dopant

Abstract

Modulating the magnetic anisotropy of ferromagnetic thin films is crucial for constructing high-density and energy efficient magnetic memory devices. Ta/W(N)/Co/Pt multilayers were deposited on silicon substrates by magnetron sputtering at room temperature. The influences of N dopant on the magnetic anisotropy of the multilayers were investigated by preparing the sample with N incorporation. The results indicate that when sputtering W target with only argon gas (Ar), Ta/W/Co/Pt sample shows in-plane magnetic anisotropy (IMA). When sputtering W target at a different amount of N2 and Ar atmosphere, it can induce perpendicular magnetic anisotropy (PMA) for proper N-doped Ta/W(N)/Co/Pt sample. When the gas flow ratio of Ar:N2 is 16:6, the effective magnetic anisotropy constant reach its maximum value of 1.68 × 105 J·m−3, which enhanced by about 400% than our past works (annealing treatment is necessary to induce PMA in Pt/Co/MgO system). X-ray diffraction (XRD) and X-ray reflection (XRR) results demonstrate that N dopants can effectively promote the formation of β-W phase and reduce the roughness of W(N)/Co interface, which are beneficial for PMA. X-ray electron spectroscopy (XPS) analysis reveals that N doping redistributes Co charges, nitrogen ions participate in electron allocation of Co and attract some electrons of Co to form orbital hybridization between Co 3d and N 2p. This may be another important reason for the PMA formation.