Spin-lattice relaxation of magnetic centers in molecular crystals at low temperature
Spin-lattice relaxation of magnetic centers in molecular crystals at low temperature
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DOI：
10.1103/physrevb.97.024427
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发表时间：
2018-01-23
影响因子：
3.7
通讯作者：
Chibotaru, Liviu F.
中科院分区：
文献类型：
--
作者：
Le Tuan Anh Ho;Chibotaru, Liviu F.
在低温下，研究了克拉默分子磁体和非克拉默分子磁体在强稀释样品中的自旋声子弛豫速率。利用“旋转”对自旋声子哈密顿量的贡献，得到了弛豫速率的通用公式。有趣的是，这些公式都完全通过可测量或从头计算的物理量来表达。此外，它们也独立于松弛过程中激发态的能量间隙。这些直接过程和拉曼过程的表达式提供了一种简单的方法来确定任何自旋系统的自旋声子弛豫的最低极限，仅基于地双偶态的磁性。此外，还发现了拉曼过程的一些有趣的性质。特别地，Kramers系统中的拉曼过程依赖于磁场的方向，但与磁场的大小无关，同时，非Kramers系统中的拉曼过程在共振（即外加一个外场）下显着减少。有趣的是，两种系统的拉曼过程随着T-9的变化而变化。将该理论应用于最近研究的钴（II）配合物表明，它可以很好地描述弛豫。基于这些发现，提出了一种通过提高分子单元的机械刚度来开发高效单分子磁体的策略。
We study the spin-phonon relaxation rate of both Kramers and non-Kramers molecular magnets in strongly diluted samples at low temperature. Using the "rotational" contribution to the spin-phonon Hamiltonian, universal formulas for the relaxation rate are obtained. Intriguingly, these formulas are all entirely expressed via measurable or ab initio computable physical quantities. Moreover, they are also independent of the energy gaps to excited states involved in the relaxation process. These obtained expressions for direct and Raman processes offer an easy way to determine the lowest limit of the spin-phonon relaxation of any spin system based on magnetic properties of the ground doublet only. In addition, some intriguing properties of Raman process are also found. Particularly, Raman process in Kramers system is found dependent on the magnetic field's orientation but independent of its magnitude, meanwhile, the same process in non-Kramers system is significantly reduced out of resonance, i.e., for an applied external field. Interestingly, Raman process is demonstrated to vary as T-9 for both systems. Application of the theory to a recently investigated cobalt(II) complex shows that it can provide a reasonably good description for the relaxation. Based on these findings, a strategy in developing efficient single-molecule magnets by enhancing the mechanical rigidity of the molecular unit is proposed.