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

通过在云母衬底上溅射制备了高度(111)取向的铂衬底。然后在其上溅射不同铂含量的钴铂合金薄膜。用X射线极图分析了所制备的Co-Pt合金薄膜的晶体结构。结果表明，铂含量大于60%的Co-铂合金薄膜具有(111)取向的面心立方(Fcc)结构，而铂含量小于40%的合金薄膜具有(0001)取向的六方密排(HCP)结构。在高度(100)取向的面心立方结构上也溅射了Co-铂合金薄膜，而与在(100)取向的氯化钠衬底上制备的铂底层无关。发现它们具有(100)取向的面心立方结构，与铂含量无关。Co-Pt合金薄膜的垂直磁各向异性与晶体结构密切相关。也就是说，具有(0001)取向的hcp结构的Co-Pt合金薄膜的垂直各向异性比具有(111)和(100)取向的面心立方结构的要高得多。铂含量在30%左右的Co-铂合金薄膜具有垂直于薄膜平面的易磁化方向。Co-Pt合金薄膜的晶体结构依赖于沉积过程中的衬底温度，当沉积温度超过200℃时，薄膜的晶体结构由(0001)面心立方结构转变为(111)面心立方结构。这种从HCP结构到面心立方结构的变化是由铂底层厚度完成的，对于大于200 nm的厚度几乎是恒定的。只要(111)取向足够高，也可以在Au或Cu底层上制备具有(0001)择优取向的Co-铂合金薄膜。少量的铬使合金的垂直各向异性略有降低。Al的加入使垂直各向异性大大降低。

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.