Preparation of Cobalt-Platinum Alloy Films with Hexagonal Close-Packed Structure for Perpendicular Magnetic Recording Application

采用溅射法在云母衬底上制备了高度（111）取向的Pt衬底。然后，在其上溅射具有不同Pt含量的Co-Pt合金膜。用X射线极图分析了Co-Pt合金薄膜的晶体结构。结果表明，Pt含量大于60%的Co-Pt合金薄膜为（111）取向的面心立方（fcc）结构，而Pt含量小于40%的Co-Pt合金薄膜为（0001）取向的六方密排（hcp）结构。Co-Pt合金膜也被溅射到高度（100）取向的fcc结构上，而与在（100）取向的NaCl衬底上制备的Pt底层无关。发现它们具有（100）取向的fcc结构，与Pt含量无关。Co-Pt合金薄膜的垂直磁各向异性与其晶体结构密切相关。也就是说，具有（0001）取向hcp结构的Co-Pt合金薄膜比具有（111）或（100）取向fcc结构的Co-Pt合金薄膜表现出更高的垂直各向异性。Pt含量在30%左右的Co-Pt合金膜具有垂直于膜面的易磁化方向。Co-Pt合金薄膜的晶体结构依赖于沉积过程中的衬底温度，当温度超过200℃时，Co-Pt合金薄膜由（0001）取向的hcp结构转变为（111）取向的fcc结构。这种从hcp到fcc结构的变化是通过Pt底层厚度实现的，对于大于200 nm的厚度，Pt底层厚度变得几乎恒定。在Au或Cu衬底上也可以制备出具有（0001）取向hcp结构的Co-Pt合金薄膜，只要衬底的（111）取向足够高。少量的Cr增强了垂直各向异性，使垂直各向异性略有降低。Al的加入大大降低了垂直各向异性。

Highly (111) -oriented Pt underlayers were prepared by sputtering them on mica substrates. Then, Co-Pt alloy films with different Pt contents were sputtered on them. The crystal structure of the Co-Pt alloy films thus prepared were analyzed by the X-ray pole figure measurements. It was revealed that the Co-Pt alloy films with Pt contents larger than 60 % take the (111)-oriented face-centered cubic (fcc) structure, whereas those with pt contents less than 40 % take the (0001)-oriented hexagonal close-packed (hcp) structure. Co-Pt alloy films were also sputtered on highly (100)-oriented fcc structure irrespective of the Pt underlayers prepared on (100)-oriented NaCl substrates. They were found to take the (100)-oriented fcc structure irrespective of the Pt content. The perpendicular magnetic anisotropy of the Co-Pt alloy films strongly depends on the crystal structure. That is, the Co-Pt alloy films with (0001)-oriented hcp structure show much higher perpendicular anisotropy than those with (111)- or (100)- oriented fcc structure. The Co-Pt alloy films with Pt contents around 30 % possess the easy magnetization direction perpendicular to the film plane. The crystal structure of Co-Pt alloy films depends on the substrate temperature during the deposition, changing from (0001)-oriented hcp to (111)-oriented fcc structure when the temperature exceeds 200℃. This change from hcp to fcc structure is accomplished by the Pt underlayer thickness, becoming nearly constant for the thickness lager than 200 nm. Co-Pt alloy films with (0001)-oriented hcp structure can also be prepared on Au or Cu underlayers provided that their (111)-orientation is high enough. A small amount of Cr enhanced the perpendicular anisotropy decrease slightly. The addition of Al results in a great reduction of the perpendicular anisotropy.