氧化物/FePt基薄膜中界面和成分对FePt有序化转变影响机理的微观研究

L1(0) ordered FePt has excellent uniaxial magnetocrystalline anisotropy and adequate coercivities, which is one of the most promissing candidate materials for the next generation of ultrahigh density magnetic recording media. However, the as-deposited FePt thin films are always of disordered A1 structure,showing characteristics of a soft-magnetic material. A high-temperature annealing is required to realize the A1 to L1(0) ordering transition. How to avoid such annealings and realize low-temperature ordering of FePt films is one of critical issues for applications. Up to now, the research work on this issue can be classified into three categories: to change compositions, to introduce interfaces and to post treat. At present, the ordering temperature of FePt films has been decreased to the range of 300-400 oC. However, from the point of view of practical use, the ordering temperature requires to be further lowered to 200-300 oC. In this proposal, we propose to achieve FePt films of lower ordering temperatures by the synergy of compositon and interface in MOx/FePtM(M:Cu,Ag) thin films. The ordering kinetics and the mechanism of interface and composition in controlling the ordering transitions of MOx/FePt, FePtM (M:Cu,Ag) films will be studied by using in-situ TEM technique. Their synergy in diffusions and rearrangements of Fe and Pt atoms will be studied by carefully observing the interactions of interface reactions, added atoms and defects. Based on the thermal vacancy-assisted phase transition of FePt, we will investigate the vacancies in FePt films by using Position Annihilation Technique (PAT), and study the relation of the number of vacancies and the ordering temperature. This work will bring us more microscopic details (e.g.,the nucleation and growth processes of L1(0) ordered domains, the effects of defects on transitions, interface reactions and diffusions) during the FePt ordering process, improving our understanding on the ordering transitions of FePt films. It will have direct impacts for developing low-temperature ordering FePt films, and accelerate the coming of practical applications of FePt films.

铁铂合金是下一代超高密度磁记录介质的理想材料，获得低有序化转变温度的FePt薄膜是实用化的关键。目前，FePt薄膜的有序化转变温度为300-400oC，但从实用角度,仍需降至200-300oC。生长和扩散激活能高是阻碍有序化转变温度进一步降低的直接原因。本项目拟以界面和成分对FePt薄膜有序化转变的微观促进机理研究为突破口，研究氧化物/FePt基薄膜中界面与成分对有序化转变的协同作用机制，探索进一步降低有序化转变温度的解决方案。拟利用原位TEM和XRD 研究MOx/FePtM(M:Cu,Ag）薄膜中界面反应、添加元素、薄膜缺陷之间的相互作用关系，揭示它们对FePt有序畴生长的影响规律与机理。基于FePt有序化转变的空位扩散机制，拟利用PAT研究Cu、Ag对FePt空位缺陷的影响规律，揭示空位缺陷与有序化转变温度的关系。通过本项目的研究，获得转变温度低、磁学性能优良的FePt基薄膜。

随着大数据、云计算等新概念的提出，大容量存储技术在信息的处理、传输和储存中发挥着越来越关键的作用。超高密度磁记录存储技术作为当前主流的大容量存储技术，对磁记录介质的性能也提出了更高的要求。有序化铁铂合金薄膜因极高的磁晶各向异性能和良好的化学稳定性而被视为下一代超高密度磁记录介质，但因较高的有序化转变温度制约了实际应用。探讨铁铂合金薄膜的有序化转变机理、探索降低有序化转变温度的可行方案是亟待解决的关键问题。本项目从成分和界面对铁铂合金薄膜有序化转变的影响机理入手，系统研究了Cu掺杂、Cu和Nb共掺、Ag掺杂、Ag和Cu共掺的FePt基合金薄膜以及引入氧化物界面的CuO/FePtCu多层薄膜的有序化转变行为。Cu掺杂结果表明，Cu含量为16.01 at.% 的合金矫顽力最高。当Cu含量低于7.89 at.%时，有序化转变温度在350到450 °C之间。当Cu含量高于10.39 at.% 时，有序化转变温度在300到350 °C之间。Cu、Nb共掺结果表明，随着Nb含量增加，FePtCuNb合金薄膜的矫顽力先增大后减小。Nb掺杂0.7 at.% 时，矫顽力超过4 kOe。微量Nb添加在保持合金低温有序性能的基础上提高了薄膜矫顽力，而进一步增加Nb含量，合金有序化温度升高。Ag掺杂结果表明，(FePt)91.2Ag8.8薄膜的平均矫顽力可达10.7 kOe，比FePt薄膜的平均矫顽力高出0.8 kOe，证明掺杂Ag有效地促进有序化转变过程。利用原位高分辨透射电子显微技术，首次在FePtAg薄膜中观察到FePt有序化转变和Ag晶界偏析同时发生的直接证据。结合XAFS谱结果，进一步揭示了Ag在制备态薄膜中取代Fe的位置，当加热至较高温度时从固溶相中析出而在晶内留下空位，空位的形成有利于Fe、Pt原子的扩散，促进了有序化转变。Cu、Ag共掺未能有效促进有序化转变，但当Cu含量接近时，矫顽力随Ag含量的增加而提高，佐证了Ag掺杂促进有序化转变的结论。CuO/FePtCu多层膜结果表明，CuO薄膜中非磁性相引入对硬磁性能的破坏作用大于增加空位对扩散的促进作用，不适合通过此方案制备硬磁性能与低温有序兼顾的薄膜。本项目的研究成果加深了人们对Cu、Ag掺杂体系中FePt低温有序化转变行为和影响机理的理解，对于基于Cu、Ag掺杂方法开展更低温度有序化转变的研究具有重要的参考和借鉴价值。