Sputtering gases and pressure effects on the microstructure, magnetic properties and recording performance of TbFeCo films

The MsHc value is considered to be a key factor in high-density recording, and controlling the microstructure on the magnetic underlayer was found to be an effective way of increasing the MsHc of the amorphous TbFeCo magneto-optical (MO) medium. In this paper, we investigate the TbFeCo film's magnetic properties and the effects on the microcolumnar structure, which depends on the sputtering conditions of using various sputtering gases including Ar, Kr, and Xe, and the recording characteristics of TbFeCo memory layers. With heavy sputtering gases such as Kr or Xe, the columnar structure can be prepared in a TbFeCo film at a pressure lower than 1.0 Pa. The columnar structure of a recording layer can be effectively formed thanks to the effects of the magnetic underlayer, which has a fine surface even in the sputtering process in which Xe gas is used. The above applies to the sputtering process in which Ar gas is used. Also, when Xe gas is used in the sputtering process, coercivity Hc is increased through the formation of a well-segregated microcolumnar structure built on domain wall pinning sites, and we obtain a large MsHc and a high squareness ratio of the Kerr-hysteresis loop. Our results indicate that processing a TbFeCo film with heavy sputtering gases is suitable for tiny mark stability because the temperature gradient of Hc is increased. The objective of the low-pressure sputtering process using Xe gas to produce the columnar structure is to achieve ultra-high-density recording with tiny mark stability in the TbFeCo medium. This has been confirmed with magnetic force microscope (MFM) images of stable tiny marks recorded on TbFeCo film.