| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 97 === In this study, the dependence of sputtering parameters on the formation of FePt(001) and CoPt(001) films was investigated. Two series of samples with the structures of Fe48Pt52(20 nm)/Pt(2 nm)/Cr91Ru9(120 nm)/glass substrate and CoPt(50 nm)/Pt(0 ~ 2 nm)/MgO(001) substrate were sequentially planetary-sputtered using an ultra-high vacuum magnetron sputtering system, and the effect of sputtering parameters on the ordering of L10-FePt and L10-CoPt films were investigated. These parameters include negative bias, Pt layer thickness, sputtering rate, deposition temperature and rotational speed of the sample holder. Film structures were analyzed by X-ray diffractometry (XRD), and magnetic properties were measured by a vibrating sample magnetometer (VSM).
For the FePt series, the degree of chemical ordering increased as the sputtering rate decreased. For the film sputtered at 1 rpm, when the sputtering rate decreased from 2.226 to 0.578 nm/min., the out-of-plane squareness increased from 0.165 to 0.557, and the out-of-plane coercivity also increased from 454 to 1923 Oe. Furthermore, when the rotational speed of the sample holder increased from 1 to 10 rpm, the FePt films exhibit higher degree of ordering and improved magnetic properties. However, when the negative bias was applied, the degree of chemical ordering declined and the orientation of easy axis switched from out-of-plane to in-plane direction.
As for the CoPt series, it has been found that the development of perpendicular anisotropy of L10-CoPt (001) films is a two-step process. First, the ordering process onsets at the temperature of 550℃ with longitudinal anisotropy. Then the perpendicular anisotropy will dominate when the deposition temperature is increased above 650℃. Futhermore, The CoPt(002) peak shifted to higher angle as the sputtering rate decreased. Also, the intensities of CoPt(001) peak was greatly enhanced by increasing the rotational speed of the sample holder from 1 to 10 rpm. These phenomenon indicate that the degree of chemical ordering can be enormously improved by increasing the rotational speed of the sample holder similar to that of FePt(001) films. This is because when the rotational speed of the sample holder increased, the thickness of Fe or Pt layer formed per revolution was also reduced, which results in the reduction of the distance which the sputtered Fe and Pt atoms have to travel into the correct lattice sites of L10 phase. Therefore, the degree of chemical ordering increased. Decreasing the sputtering rate has a similar effect to that of increasing the rotational speed of the sample holder.
By combining low-sputtering-rate and high-rotaional-speed process, we successfully reduced the ordering temperature of FePt to 300℃, which is 50℃ lower than in previous reports. These results herein provide useful information on the fabrication of FePt(001) and CoPt (001) thin films in media use.
|
|---|
