CoCrTa/Cr longitudinal recording media is one of the most widly used composition at the present time. As the recording density increases annually, the higher coercivity is desirable. There are two routes to increase the coercivity at a given sputtering condition ; one is to change the composition of the magnetic layer and the other is modification of Cr underlayer by adding a second element such as V, Ti and others. The present study is aimed to increase the coercivity of $CoCr_{10}Ta_4$ films by adding V and Ta into Cr underlayer and to analyze the cause of the coercivity increase.
By the addition of V and Ta, the maximum coercivity in $CoCr_{10}Ta_4$ films was 2350 Oe in the both cases which correspond about 10% coercivity improvements. V addition showed slow increase of the coercivity and showed the maximum coercivity around 8 at% V. However, Ta addition showed rapid increase of the coercivity and showed the maximum coercivity around 1.5 at%. Saturation magnetization of CoCrTa film showed rather rapid decrease with the addition of the both elements into Cr underlayer. Auger depth profile analysis showed no evidence of intermixing between the magnetic layer and the underlayer. The cause of the saturation magnetization decrease is not known.
The reasons for the coercivity increase were analyzed in terms of orientation change of Co alloy due to the change of orientation of Cr underlayer due to the additives and of grain size change. When V was added Cr(002) peak intensity increased and Cr(110) peak seems slightly decreased. At the optimum Ta addition, Cr(002) peak was also the strongest. In spite of strong Cr(002) texture, Co$(11\bar{2}0)$ texture development was very weak.
The summation of normalized Co$(10\bar{1}0),(10\bar{1}1)$, and $(11\bar{2}0)$ intensities which contributes in plane coercivity was compared for pure Cr and Ta and V added Cr underlayers. However, an conclusive interpretation of orientation contribution was not obtained as separation of Co(0002) peak and Cr(110) peak was not possible.
The grain size of the three different underlayers and subsequently deposited Co magnetic layers were calculated by Scherrer formula from XRD data. It was found that grain sizes of the alloyed underlayers and subsequent Co magnetic layers were smaller than that of pure Cr underlayers and subsequent Co magnetic layers. However, TEM analysis showed the contracting result in the case of the underlayers. If the X-ray grain size results should be the more realistic in large area, the smaller grain size will contributes to the increase of the coercivity.
It has been reported a micromagnetic calculation[42] that the reduced saturation magnetization contributes to the increase of the coercivity. This may also contributes the coercivity increase.
A conclusive cause of the coercivity increase was not found in the present work.
