Departament de Química Inorgànica and Institut de Recerca de Química Teòrica i Computacional, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza, Spain.
Nat Commun. 2014 Jul 1;5:4300. doi: 10.1038/ncomms5300.
Transition metal ions with long-lived spin states represent minimum size magnetic bits. Magnetic memory has often been associated with the combination of high spin and strong uniaxial magnetic anisotropy. Yet, slow magnetic relaxation has also been observed in some Kramers ions with dominant easy-plane magnetic anisotropy, albeit only under an external magnetic field. Here we study the spin dynamics of cobalt(II) ions in a model molecular complex. We show, by means of quantitative first-principles calculations, that the slow relaxation in this and other similar systems is a general consequence of time-reversal symmetry that hinders direct spin-phonon processes regardless of the sign of the magnetic anisotropy. Its magnetic field dependence is a subtle manifestation of electronuclear spin entanglement, which opens relaxation channels that would otherwise be forbidden but, at the same time, masks the relaxation phenomenon at zero field. These results provide a promising strategy to synthesize atom-size magnetic memories.
具有长寿命自旋态的过渡金属离子代表了最小尺寸的磁比特。磁性记忆通常与高自旋和强单轴各向异性的结合有关。然而，在一些具有主导易面各向异性的克拉默斯离子中，也观察到了缓慢的磁弛豫，尽管只是在外磁场下。在这里，我们研究了模型分子配合物中钴（II）离子的自旋动力学。我们通过定量的第一性原理计算表明，这种和其他类似系统中的缓慢弛豫是时间反演对称性的普遍结果，它阻碍了直接的自旋-声子过程，而与磁各向异性的符号无关。其磁场依赖性是电子-核自旋纠缠的微妙表现，它开辟了原本会被禁止的弛豫通道，但同时也掩盖了零场下的弛豫现象。这些结果为合成原子尺寸的磁性存储器提供了一个有前途的策略。
