The effect of amorphous FeTi seedlayer on the magnetic properties of CoCrX(X=Pt, Ta)/Cr magnetic thin film was investigated by controlling the sputtering conditions, especially through the variation of applied bias. The application of FeTi seedlayer increased the coercivity of CoCrX/Cr magnetic thin film by more than 1000 Oe under the negative bias condition. This high coercivity increase primarily resulted from the texture change of the Cr underlayer and subsequently of the CoCrX magnetic layer. By applying bias to the FeTi seedlayer, the coercivity of CoCrX/Cr magnetic thin film decreased due to the texture change of Cr and CoCrX layer. But the bias application to the Cr underlayer CoCrX magnetic layer resulted in the increase of the coercivity of CoCrX/Cr/FeTi magnetic thin films. In case of Cr underlayer, the applied bias induced a lattice expansion and a grain growth. Substrate bias was very important factor in controlling the composition and thickness of magnetic layer, optimizing the magnetic properties. Applied bias in CoCrPtTa alloy target decreased the composition of Co by increasing the composition of Pt due to resputtering effect. But the composition of Cr and Ta little changed. Generally optimum bias was -150V in CoCrX/Cr magnetic thin film systems, but it increased to -300V on introducing FeTi seedlayer. As a result, more Pt could be incoporated into the magnetic layer, which resulted in an enhancement of the magnetocrystalline anisotropy constant. In addition to, applied bias in CoCrPtTa magnetic layer significantly decreased the deposition rate of the film. The decrease of magnetic layer thickness is important because low Mrt is desirable for high density recording. As the thickness of Cr underlayer increased, coercivity increased due to an enhancement of Co(10.0) texture and a maximum coercivity was found at the film thickness of 50nm.
A CrTi underlayer in place of Cr underlayer was found to further increase the in-plane coercivity of CoCrPtTa/Cr/FeTi magnetic thin film systems: the maximum coercivity obtained was about 3300Oe for CoCrPtTa/Cr94Ti6/FeTi magnetic thin film systems. The lattice matching of CrTi underlayer with Co films was better than that of Cr underlayer, improving the epitaxial growth of Co(10.0) planes. CrTi underlayer further more induced a significant reduction of grain size of magnetic layer.
