化学计量比FePt和CoPt合金的表面能及其对纳米颗粒形貌的影响
Surface energies of stoichiometric FePt and CoPt alloys and their implications for nanoparticle morphologies
摘要：
我们用密度泛函理论计算了单原子Fe、Co和Pt以及二元有序FePt、CoPt和MnPt的各种低指数表面的表面能和表面磁序。我们的研究结果表明，元素，Pt覆盖的表面是首选的Fe和Co覆盖和混合表面相同的取向。混合表面的最低能量取向是高度配位的（111）表面。我们发现Pt覆盖的（111）表面，这只能在L11结构中实现，与混合L10（111）表面相比，能量低约400 meV/atom。我们的结论是，这种低表面能稳定的L11结构的小纳米粒子，这是抑制在块体合金，但最近已合成的薄膜的CoPt。从表面能和体积能的相互作用，可以估计单晶有序纳米颗粒的平衡形状和不同排序之间的交叉尺寸。
英文摘要：
We have calculated surface energies and surface magnetic order of various low-indexed surfaces of monoatomic Fe, Co, and Pt, and binary, ordered FePt, CoPt, and MnPt using density functional theory. Our results for the binary systems indicate that elemental, Pt-covered surfaces are preferred over Fe- and Co-covered and mixed surfaces of the same orientation. The lowest energy orientation for mixed surfaces is the highly coordinated (111) surface. We find Pt-covered (111) surfaces, which can be realized in the L11 structure only, to be lower in energy by about 400 meV/atom compared to the mixed L10 (111) surface. We conclude that this low surface energy stabilizes the L11 structure in small nanoparticles, which is suppressed in bulk alloys, but has been recently synthesized as thin film for CoPt. From the interplay of surface and bulk energies, equilibrium shapes of single-crystalline ordered nanoparticles and crossover sizes between the different orderings can be estimated.
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