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Evidence of local structural influence on the shape driven magnetic anisotropy in electronically excited Ni nanoparticles embedded in SiO2 matrix

机译:SiO2基体中嵌入的电子激发Ni纳米粒子的局部结构影响形状驱动磁各向异性的证据

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摘要

The reliance of modern electronic era on ultrafast data recording has made the search for novel tools to tune nano-scale magnetic-anisotropy (MA) never-ending. We demonstrate a strong correlation between the spin-spin interactions, local atomic structure and the MA of Ni nanoparticles (NPs) embedded inside SiO2 matrix under swift heavy ion (SHI) irradiation. In contrast to traditional understandings, MA in Ni NPs along with their aspect ratio, first increases upto 5 × 1013 ions/cm2 SHI fluence (5e13) and gets reduced at highest fluence. Using angle dependent Extented-Xray-Absorption-Fine-Structure (EXAFS) and ab initio molecular dynamics (MD) simulations, we show that the anisotropy induced in local atomic structure upon irradiation is dependent on atomic spin-spin interactions, which gets reduced at highest fluence. The chosen model cluster (Ni38) used in our MD simulations is duly validated by comparing the pair-correlation-function of the structure with the EXAFS-Fourier-Transform. The lattice temperatures for the films irradiated at different fluences, as calculated from thermal-spike-model, are used for the respective MD runs. We conclude that the enhanced disorder in both the local atomic environment and spin alignment destroys the MA at the highest fluence in SHI irradiated Ni NPs. The findings therefore provide rich conceptual insights for designing magnetic devices using SHI-induced phenomena.
机译:现代电子时代对超快数据记录的依赖使得寻找新颖的工具来调谐纳米级磁各向异性(MA)永无止境。我们展示了自旋-自旋相互作用,局部原子结构和快速重离子(SHI)照射下嵌入SiO2基质中的Ni纳米颗粒(NPs)的MA之间的强相关性。与传统理解相反,Ni NP中的MA及其长宽比首先增加至5×10 13 离子/ cm 2 SHI通量(5e13),并在最高通量。使用依赖于角度的扩展X射线吸收精细结构(EXAFS)和从头算分子动力学(MD)模拟,我们显示了在局部原子结构上辐照引起的各向异性取决于原子自旋-自旋相互作用,在最高通量。通过将结构的成对相关函数与EXAFS-Fourier变换进行比较,可以正确验证在我们的MD仿真中使用的所选模型簇(Ni38)。根据热峰模型计算,以不同注量辐照的薄膜的晶格温度分别用于各个MD行程。我们得出的结论是,在局部原子环境和自旋排列中增强的无序都以SHI辐照的Ni NP的最高通量破坏了MA。因此,这些发现为使用SHI感应现象设计磁性设备提供了丰富的概念见解。

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