Crystal structure and magnetic properties of Pb substituted Ba-ferrite sputtered films for perpendicular magnetic recording media (abstract)

Abstract

Ba-ferrite (BaM) sputtered films are suitable for a high density perpendicular recording medium.1 There were some problems to be solved in preparing BaM films. One of the most important problems is that a high substrate temperature Ts was necessary. Ts for preparing BaM films with c-axis dispersion angle Δθ50 as small as 2°–3° is about 620 °C and a high Ts limits the selection of substrate material. In this paper, Pb substituted BaM[(Ba⋅Pb)M] films were prepared by dc magnetron sputtering and their crystal structure and magnetic properties were studied. The substrate is a thermally oxidized silicon wafer. The target is a sintered ferrite disk (8 cm diameter) with stoichiometric composition of BaM and Pb content was controlled by the numbers of Pb chips on this disk. Argon and oxygen gas were introduced into a chamber and discharge gas pressure was set at 2 mTorr. Partial oxygen gas pressure was 0.01 mTorr and an applied power was 50 W. The thickness of (Ba⋅Pb)M films was about 1500 Å. The films prepared at Ts below 300 °C were amorphous and those prepared at Ts ranging from 300 to 400 °C consisted of spinel-like phase. Saturation magnetization Ms of these films was almost zero. The films prepared at Ts above 400 °C consisted of both hexagonal and spinel-like ferrites.2 Intensity of diffraction lines from hexagonal ferrite became strong as Ts was elevated and those for hexagonal ferrite were only from c-plane such as (004), (006), (008), (0010), (0012), and (0014). Usually, the lines from the (004), (0010), and (0012) planes cannot be observed in bulk BaM. This implies that the c axis is well oriented perpendicularly to the film plane. (Ba/Pb)M films prepared at Ts about 520 °C possess Δθ50 of about 1°, Hc⊥ of 1.0 kOe, and Ms of about 250 emu/cc.