Multilayered films of Co/Pd were investigated as a candidate materials for a high density recording media. Co/Pd multilayered films have higher perpendicular anisotropy energy than the conventional CoCr alloy perpendicular media. They have the advantages of large output signals and negligible magnetization relaxations. However, high exchange coupling between grains in Co/Pd multilayered films results in large transition noises which is undesirable in high density magnetic recording. Recently, many researchers made efforts to decrease grain size and exchange coupling of Co/Pd multilayered films by adding 3rd elements to Co or Pd sublayers or producing physically separated grains in deposition process.
In this study, to reduce exchange coupling in Co/Pd multilayered films, we studied on effects of sputtering parameters on magnetic properties in Co/Pd multilayered films. The Co/Pd multilayered films were deposited by a D.C. magnetron sputtering method with the following layer structure ; Ti(50Å)/Pd(tÅ)/[Co(aÅ)/Pd(bÅ)]× 25
In the first part, we studied on effects of Ar sputtering pressure on the properties in Co/Pd multilayered films. In this part we studied Ti(50Å)/Pd(200Å)/[Co(5Å)/Pd(9Å)]× 25 multilayered films deposited at 5mTorr and 25mTorr pressure. Co/Pd multilayered films deposited at Ar 25mTorr sputtering pressure have more sheared hysteresis loops than those at Ar 5mTorr. The saturation magnetization(Ms) of Co/Pd multilayered films deposited at Ar 25mTorr was 210 emu/cc. Ms at Ar 25mTorr is less than 50% of Ms of the films deposited at Ar 5mTorr. The reason of the decrease is considered to be associated with enhanced mixing of Co and Pd at higher sputtering pressure, mainly.
Co/Pd multilayered films deposited at Ar 25mTorr have weaker grain exchange coupling than those at Ar 5mTorr. In the cross section TEM images, Co/Pd multilayered films deposited at the higher Ar sputtering pressure showed clear physical separation at the column boundaries. These physically separated grains results in weak grain exchange coupling. The micro structural observations is in consistent with domain observation. The multilayered films deposited at 5mTorr showed stripe domains but those deposited at 25mTorr showed dotted domains with reduced domain size of 135nm.
Read/Write characteristics of the two type films tested by a linear motion stand showed high output voltage at lower frequency and lower output voltage at higher frequency for the 5mTorr deposited film. The trend was similar for the 25mTorr film but the reduction of output at higher frequency was much slower. This indicates the films deposited at 25mTorr would be favorable for higher density application although noise properties were not measured.
In the second part, effects of Co sublayer thickness on magnetic properties of Co/Pd multilayered films have been studied. Ms (of Co volume) of Co/Pd multilayered films at Ar 5mTorr was larger than that of bulk Co. In the case of Ar 25mTorr, Ms was % of bulk Co and decreased as increasing Co sublayer thickness. Co/Pd multilayered films with very thin Co sublayer thickness (3-4Å) have a alpha value smaller than 1 and high coercivity larger than 6000 Oe.
In the third part, effects of Pd buffer layer thickness on the properties of Co/Pd multilayered films have been investigated. Coercivity and exchange coupling of Co/Pd multilayered films varied with varying Pd buffer layer thickness. As decreasing Pd buffer layer thickness, the exchange slope of the multilayered films decreased. It is due to the decrease of physical separations between columnar grains. In the AFM image, Pd 200Å buffer layer has a more rough surface than Pd 50Å. The roughness of Pd buffer layer seem to be clearly associated with physically separated columnar grains at higher pressure sputtering condition.
