Magnetic and structural properties of CoNiPt(SiO2) alloy films for high-density longitudinal recording

Abstract

Magnetic and structural properties of sputtered CoNiPt(SiO2) alloy films have been studied for high-density longitudinal recording media. In-plane coercivity remarkably increases from 1400 to 2500 Oe with an increase of SiO2 content up to 4 at. % and coercive squareness S* slightly decreases from 0.90 to 0.87, while the perpendicular magnetic anisotropy is not changed significantly. Media noise is markedly reduced by the addition of SiO2. Si in the film is shown to be in the form of SiO2 by x-ray photoelectron spectroscopy. In x-ray diffraction, hcp-CoNiPt lattice is observed and the lattice constants of this hcp structure are expanded by the SiO2 addition. Relative integrated intensities of the diffraction peaks from (100) and (002) planes to (101) plane are not dependent on the SiO2 content, which indicates that the average orientation of the c axis of the hcp lattice is not influenced by the SiO2 addition. This agrees with the result that the perpendicular anisotropy is not significantly changed. From the transmission electron microscopy and high-resolution scanning electron microscopy analyses, grain size decreases with the SiO2 addition. Moreover, the outline and shape of crystal grains become sharper with the SiO2 addition of 2 at. % than those in pure CoNiPt. With the 4 at. % SiO2, clear separation among each crystal grain is observed. These changes of the grain structure by the SiO2 addition are attributed to the chemical segregation of the SiO2 at the grain boundary. It is concluded that the development of this grain separation is a major reason for remarkable increase in the coercivity and reduction of the media noise by the SiO2 addition.