CoPt及(CoPt)1-y(SiNx)y薄膜的製作與磁性質研究

Abstract

Co50Pt50 films were deposited at room temperature by dc magnetron sputtering, and were combined with MgO underlayer, Ag underlayer, and SiNx capped layer to form Co50Pt50/MgO, Co50Pt50/Ag, SiNx/Co50Pt50/Ag, and (Co50Pt50)1-x(SiNx)x/Ag multilayer films on glass substrates. The effects of MgO underlayer, Ag underlayer, SiNx capped layer, and process parameters on the microstructure, magnetic properties, and magnetic easy axis of the film were investigated. For the fabrication of MgO underlayer with MgO(200) preferred orientation, the process parameters are 20 sccm Ar flow rate, 5 mTorr Ar pressure, 150 w rf power, and 360 nm film thickness. For the CoPt (20 nm)/ MgO (360 nm) films, the the effect of MgO(200) underlayer on the epitaxial growth of CoPt layer is not obvious due to the rough interface between CoPt and MgO and the diffusion of Co and Pt atoms into MgO underlayer during heat treatment. It can not make the magnetic easy axis of CoPt perpendicular to the film plane. For the CoPt/Ag films, the introduction of Ag underlayer could lower the ordering temperature of CoPt film. The ordering temperature decreases from 650°C of single-layered CoPt to 500~550°C and Ag underlayer has the effect of promoting out-of-plane magnetic properties of CoPt films. After annealing at 650°C for 30 minutes, the CoPt (20nm)/ Ag (25 nm) film shows best out-of-plane magnetic properties and its Hc⊥ value = 13000 Oe, Hc∥ value = 12300 Oe, Ms value = 420 emu/cm3, S⊥ = 0.9, and S∥ value= 0.38. A 32 nm SiNx capped layer was deposited on the top of CoPt/Ag film then annealed at 650°C for 30 minutes. The I001 /I111 ratio of CoPt (20 nm)/ Ag (25 nm) film decreases from 13.05 without SiNx capped layer to 1.54 with SiNx capped layer. Its Hc⊥ value = 11600 Oe, Hc∥ value = 9900 Oe, Ms value = 520 emu/cm3, S⊥ = 0.88, and S∥ value= 0.41. It was found that SiNx capped layer would inhibit CoPt(001) orientation growth and promote CoPt(111) preferred orientation. After annealing at high temperature, SiNx capped layer could reduce the oxidation of CoPt film, and the Ms value of the film was enhanced from 420 emu/cm3 to 520 emu/cm3. After annealing at 650°C and 700°C for 30 minutes, it is found that SiNx will limit the out-of-plane magnetic anisotropy of (Co50Pt50)1-y(SiNx)y (20 nm)/Ag (25 nm) granular films. SiNx would inhibit CoPt(001) preferred orientation. From the observation of TEM, when SiNx = 4.3 vol%, partial granular structure is observed, but the particle size and distribution are not uniform. When SiNx = 50 vol%, the uniformity of particle size and distribution is better, however, the magnetic easy axis is random and not perpendicular to the film plane.