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Surfactant-mediated growth of ferromagnetic Mn δ-doped Si

机译：表面活性剂介导的铁磁Mnδ掺杂硅的生长

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We present an investigation of Mn δ-doped layers in Si(OOl) grown by molecular beam epitaxy. We discovered that a Pb surfactant has significant effect on the structural and magnetic properties of the submonolayer of Mn, which depends on the Si capping layer growth temperature T_(Si), and the Mn coverage θ_(Mn). The results presented in this paper identify three regions in the growth-phase diagram characterized by distinct magnetic behaviors and crystal structures. In one region, x-ray absorption fine structure and transmission electron microscopy experiments indicate that MnSi nanocrystallites form with B2-like crystal type structures. At the optimal growth conditions, T_(Si) = 200 ℃ and θ_(Mn) = 0.26 monolayer, a ferromagnetic phase develops with a Curie temperature T_C ＞ 400 K and a saturation moment m_(sat), = 1.56 /μ_B/Mn, whereas T_C drops to zero for a control sample prepared without Pb. For T_(Si) ＞ 200 ℃ MnSi-B20 type precipitates form with a T_C≈ 170 K. Rutherford backscattering spectrometry shows that the increase in the remanent magnetization in these two phases is possibly correlated with an increase in the Mn substitutional fraction, which suggests that a Si_(1-x)Mn_x dilute magnetic semiconductor may be forming in the matrix between the precipitates. Density functional calculations show that Pb changes the pathway by which the Mn atoms access the Si substitutional sites, Mn_(Si). While the Pb increases the formation energy of Mn_(Si) at the Si surface, it enables substitutional incorporation by lowering the formation energy of Si vacancies by 0.92 eV.
机译：我们目前对分子束外延生长的Si（OOl）中Mnδ掺杂层的研究。我们发现，Pb表面活性剂对Mn亚单层的结构和磁性有重要影响，这取决于Si覆盖层的生长温度T_（Si）和Mn覆盖度θ_（Mn）。本文提出的结果在生长相图中确定了三个区域，这些区域的特征是明显的磁行为和晶体结构。在一个区域中，x射线吸收精细结构和透射电子显微镜实验表明，MnSi纳米微晶以B2样晶体类型结构形成。在最佳生长条件下，T_（Si）= 200℃，θ_（Mn）= 0.26单层，在居里温度T_C＞ 400 K和饱和力矩m_（sat）= 1.56 /μ_B/ Mn的条件下形成铁磁相，而对于不含Pb的对照样品，T_C降至零。对于T_（Si）＞ 200℃的MnSi-B20型析出物，T_C≈170K。卢瑟福反向散射光谱法表明，这两个相中剩余磁化强度的增加可能与Mn取代分数的增加有关。在析出物之间的基质中可能形成了Si_（1-x）Mn_x稀磁半导体。密度泛函计算表明，Pb改变了Mn原子进入Si取代位点Mn_（Si）的途径。虽然Pb增加了Si表面Mn_（Si）的形成能，但它通过将Si空位的形成能降低0.92 eV来实现取代结合。

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