|Alternative Title||Investigation on the magnetic properties of negative magnetocrystalline anisotropic CoIr soft magnetic layer based ECC media|
|Place of Conferral||兰州|
|Keyword||负磁晶各向异性 CoPt/CoIr薄膜 ECC介质 交换耦合|
垂直磁记录在存储介质中仍然占据重要的位置，但记录过程中因其“高记录密度、热稳定性和易写性”三者之间的制约关系，在提高记录密度方面一直受阻。为了解决这一问题，人们提出许多基于垂直磁记录技术的新材料和新工艺。交换耦合复合介质(简称ECC media)由于其具有较低的矫顽力同时能够保持较高的热稳定性以及在实验中容易制备而受到研究人员的广泛地关注。ECC介质由软磁层与硬磁层构成，并且存在两种耦合方式：(1) 直接耦合，硬磁层和软磁层直接接触；(2) 间接耦合，在软磁层和硬磁层之间加入中间层减小双层耦合强度。大量研究结果表明，复合介质中使用具有负磁各向异性能的软磁材料耦合硬磁层有助于降低整个颗粒的反转场，因此，我们选择具有强负磁晶各向异性的CoIr软磁材料去耦合硬磁层，试图降低介质的矫顽力。利用磁控溅射制备一系列性能优良的CoPt/CoIr ECC介质薄膜，研究薄膜的晶体结构、静态磁性及微观结构等。最后从理论模型出发加以验证。本论文的主要研究内容如下：
2.CoPt/CoIr ECC介质薄膜的制备及磁性研究。在CoPt硬磁层表面上直接生长CoIr软磁层得到具有Si(SiO2)/Ta/Pt/Ru/CoPt/CoIr层状结构的ECC介质薄膜。透射电镜结果显示CoPt硬磁层具有分离均匀的柱状颗粒结构，且外延生长的CoIr软磁层显示出相同的结构。静态磁性测量的结果显示CoPt和CoIr双层薄膜之间存在很强的交换耦合作用，CoPt/CoIr ECC介质的矫顽力随着CoIr软磁层厚度的增加迅速降低。同时实验结果得到理论计算的验证。
3.CoPt/Pt/CoIr ECC介质薄膜的制备及磁性研究。实验中进一步在CoPt和CoIr之间溅射生长Pt中间层，调节两层之间的耦合强度，观察CoPt/Pt/CoIr ECC介质磁性的变化，实验中制备三组不同CoIr软磁厚度的CoPt/Pt/CoIr复合样品。磁性测量的结果表明中间层Pt的使用可以提高介质的矩形比，增大矫顽力，有效地降低软磁层和硬磁层之间的交换耦合强度。然而，随着Pt层厚度的增加，软磁层和硬磁层之间的交换耦合强度逐渐变小，复合介质的矫顽力增加。
Perpendicular magnetic recording is still important, its storage density is aproaching physical limit due to the so-called “trilemma problem” encountered in the development of magnetic recording media. In order to solve this problem, many new materials and technologies based on perpendicular magnetic recording have been put forward by researchers. Exchange coupled composite media (ECC media), as a new type of perpendicular magnetic recording media, has attracted much attention since it can decrease the coercivity while maintaining the thermal stability. In general, ECC media is composed of soft and hard magnetic layers, and can be divided into two kinds of coupling structures, which are: (1) the direct coupling structure with the hard and soft magnetic layers in direct contact and (2) the indirect coupling structure with a middle layer between the soft and hard magnetic layers. A large number of research results show that the soft magnetic layers with negative magnetocrystalline anisotropy can help to reduce the reversal field of the composite particles, that is, the magnetic moment of the hard layer is much easier to turn over under the influence of the soft layer. Therefore, we choose CoIr with strong negative magnetocrystalline anisotropy and high saturation magnetization as the soft magnetic layer of our ECC media. A series of CoPt/CoIr ECC media thin films with excellent properties were prepared by magnetron sputtering. The crystal structure, static magnetic properties and microstructure of the prepared films were studied. The main contents of this thesis are as follows:
1.Preparation of CoPt hard layer with high perpendicular magnetic anisotropy. In order to induce the c-axis orient growth of the CoPt hard layer with excellent mangetic properties, we first prepared the seed-layers of Ta, Pt, and Ru with very good properties. In this thesis, the sputtering conditions (sputtering pressure, power and film thickness) of the thin films are explored by means of control variables method. By comparing the crystal structure and static magnetic properties of our films obtained under different conditions, we have obtained the optimal sputtering conditions for preparing the CoPt hard magnetic layer. This is the foundation for further preparation of the ECC media investigated in this thesis.
2.Preparation and magnetic properties of CoPt/CoIr ECC media thin films. ECC media with a layered structure of Si-substrate/Ta/Pt/Ru/CoPt/CoIr were prepared by growing CoIr soft layer on top of the CoPt hard layer following the same procedure. Transmission electron microscopy (TEM) results show that the hard-layer of our sample exhibits a columnar type microstructure with well isolated grains and the soft layer with hcp-structure grows on top of the hard layer with the same texture. Therefore, strong coupling of the two layers have been realized as evidenced by the magnetic characterization. Importantly, we observe a more effective reduction of the coercivity of the ECC media by using soft layers with negative magnetocrystalline anisotropy when compared to the use of soft layers with positive or negligible magnetocrystalline anisotropy. The experimental results are corroborated by theoretical calculations.
3.Preparation and magnetic properties of CoPt/Pt/CoIr ECC media thin films. In order to get CoPt/Pt/CoIr ECC media films with better perpendicular magnetic anisotropy, we have prepared three groups of CoPt/Pt/CoIr composite films with different CoIr soft layer thicknesses. Our results show that the introduction of the Pt interlayer can effectively reduce the exchange coupling strength between the soft and hard magnetic layers, thus increasing the rectangular ratio of the media and increasing the perpendicular magnetic anisotropy of the whole film. However, as the thickness of the Pt layer increases, the exchange coupling strength between the soft and hard layers decreases, leading to an increasement of the coercivity of the ECC media.
|焦娟莹. 基于负磁晶各向异性CoIr软磁薄膜ECC介 质的磁性研究[D]. 兰州. 兰州大学,2018.|
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