Cold homogenization of Fe/Pt based layered thin films induced by diffusion processes

功能薄膜在微纳电子等现代技术中发挥着重要作用，使其技术发展取得了重大突破。对于不同的薄膜应用领域，有必要了解薄膜异质结不同组分之间相互作用和扩散过程的物理过程。薄膜中扩散的特点之一是，扩散距离小，材料中的高水平缺陷促进，即使在低温下也能有足够的传质。缺陷可能导致强烈的扩散增强，从而可能导致亚稳相的形成，这并不对应于任何平衡状态。本项目建议致力于在Fe/PT基异质结中的扩散过程，在低温退火期形成具有特定组织的L10有序FePT相。L10有序FePT薄膜由于其优异的磁性能，包括高的磁各向异性，在应用于磁记录介质的情况下，导致磁记录密度的急剧增加，引起了人们的极大兴趣。在我们的研究中，不同的中间层将促进L10有序的形成(X和两者都表现出在FePT合金-Tb，C或形成三元合金-Mn中的不混溶)。在这种情况下，扩散过程以晶界扩散为主，体扩散可以忽略不计。基于定向扩散过程，甚至可以实现磁特性在层堆栈中变化的梯度FePT磁性薄膜。在低温退火过程中，将特别注意外加磁场的影响。假设磁场可能影响形核阶段，进而影响L10相的形成温度和取向。此外，磁致伸缩效应可能会随着合金的形成而发展，这将对应力诱导有序化动力学产生很大影响。这些研究将伴随着分子动力学模拟，以提取原子水平上的扩散机制。

Functional thin films play an important role in modern technologies such as in micro- and nano-electronics, which allowed great breakthroughs in their technological development. For different areas of thin film application, it is necessary to understand the physics of interaction and diffusion processes between different components of thin film heterostructures. One of the features of diffusion in thin films is the sufficient mass transport even at low temperatures given by the small diffusion distances and promoted by a high level of defects in these materials. Defects may induce strong diffusion enhancement and thus may lead to metastable phase formation, which do not correspond to any equilibrium state.The project proposal is devoted to diffusion processes in Fe/Pt based heterostructures during low temperature annealing forming the L10 ordered FePt phase with a specific microstructure. L10 ordered FePt thin films have attracted a lot of interest due to their excellent magnetic properties, including high magnetic anisotropy, leading to drastic increase of magnetic recording density in the case of application of this material as magnetic recording medium. In our study the L10 ordering formation will be promoted by different intermediate layers (X, both, showing non-miscibility in FePt alloy - Tb, C or forming ternary alloys - Mn). In this case, the diffusion process is dominated by grain boundary diffusion as bulk diffusion can be neglected. Based on directional diffusion processes even graded FePt magnetic thin films, where the magnetic properties vary within the layer stacks, can be realized.Special attention will be given to the impact of an applied external magnetic field during low temperature annealing. It is assumed that the magnetic field might influence the stage of nucleus formation, which in turn affects the L10 phase formation temperature and orientation. Furthermore, magnetostrictive effects might develop with alloy formation, which is expected to have a large impact on stress-induced ordering kinetics. These studies will be accompanied by molecular dynamic simulations in order to extract diffusion mechanisms on the atomic level.