Open-shell carbon-based diradical magnets have received substantial attention, owing to promising applications in molecular spintronics. However, as is known for most reported π-type diradical systems, their intrinsic high activity is a great challenge in practical applications. Here, we explore a stable σ-type silicon-vacancy (SiV⁰) nanodiamond and for the first time reveal its spin coupling characteristics, as well as its response to temperature and applied electric field, using DFT calculations combined with ab initio molecular dynamics simulation. The results indicate that the static SiV⁰ nanodiamond presents triplet diradical character with extremely strong ferromagnetic J-coupling (1913.8 cm^–1), and intriguing anisotropic response to temperature and applied electric field. Temperature-manipulated J-coupling presents persistent oscillation due to the mobility of the doping Si modifying the multiradical distribution character. Statistics indicates that the ferromagnetic J-coupling constants of SiV⁰ mainly oscillate in the range of 1400–1900 cm^–1 at 25 K, but its distribution is considerably widened and downshifted at 300 K. Under applied electric field, the ferromagnetic coupling strength of the SiV⁰ center exhibits noticeably anisotropic response to the electric field direction. Further, the zero-field splitting (D) of SiV⁰ presents a sensitive anisotropic response to an applied electric field, featuring a considerable increase of the D value to 1.43 GHz when the electric field is along the C_3v axis direction, signifying that the SiV⁰ system has excellent potential as a qubit. This work provides insights into the dynamic spin coupling characteristics in such multiradical centers of Si-doped defect nanodiamonds and facilitates the development of SiV⁰ for applications in quantum information science.

中文翻译：

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磁通掺杂-Si 控制硅空位缺陷纳米金刚石的自旋耦合特性


由于在分子自旋电子学中的前景广阔的应用，开壳碳基双自由基磁体受到了广泛关注。然而，正如大多数报道的 π 型双自由基系统所知道的那样，它们的本征高活性在实际应用中是一个巨大的挑战。在这里，我们探索了一种稳定的σ型硅空位 （SiV⁰） 纳米金刚石，并使用 DFT 计算结合 ab initio 分子动力学模拟，首次揭示了其自旋耦合特性，以及它对温度和施加电场的响应。结果表明，静态 SiV⁰ 纳米金刚石呈现三重双自由基特性，具有极强的铁磁 J 耦合 （1913.8 cm^–1），并且对温度和施加电场具有有趣的各向异性响应。由于掺杂 Si 的迁移率改变了多根分布特性，温度操纵的 J 耦合呈现持续振荡。统计数据表明，SiV⁰ 的铁磁 J 耦合常数在 25 K 时主要在 1400–1900 cm^–1 范围内振荡，但在 300 K 时其分布明显扩大和下移。在外加电场作用下，SiV⁰ 中心的铁磁耦合强度对电场方向表现出明显的各向异性响应。此外，SiV⁰ 的零场分裂 （D） 对施加的电场表现出敏感的各向异性响应，当电场沿 C_3v 轴方向时，D 值显着增加到 1.43 GHz，这表明 SiV⁰ 系统具有作为量子比特的出色潜力。 这项工作为了解 Si 掺杂缺陷纳米金刚石这种多自由基中心的动态自旋耦合特性提供了见解，并促进了 SiV⁰ 在量子信息科学中的应用开发。