Ceglarska Magdalena, Stefańczyk Olaf, Ohkoshi Shin-Ichi, Majcher-Fitas Anna M
Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Łojasiewicza 11, 30-348 Krakow, Poland.
Dalton Trans. 2020 May 28;49(20):6807-6815. doi: 10.1039/d0dt01058h. Epub 2020 May 6.
Single ion magnets have long been considered good prospective candidates to record a bit of information. One of the smallest known single ion magnets is CoBr(pyridine). This molecular compound exhibits slow relaxation of magnetization mainly due to the thermally activated Orbach process, [A. M. Majcher et al., Chem. Sci., 2018, 9, 7277-7286]. However, the total relaxation time is dramatically shortened at low temperatures due to the direct, Raman, and quantum tunneling of magnetization processes. At low temperatures, the distribution of the probability of the possible relaxation pathways in this case favours QTM and the direct process over the Orbach process. To prolong the relaxation time, the compound was diluted with diamagnetic Zn, producing 5 analogues of the general formula: CoZnBr(pyridine) (x = 0.91, 0.67, 0.43, 0.24, and 0.06), confirmed to be a solid solution by independent experimental techniques (powder X-ray diffraction, infrared spectroscopy). The presence of diamagnetic Zn ions changes the distribution of the dipolar interactions between the Co centres in the material, which results in a monotonous change in the relaxation times, which in turn become longer with increasing dilutions, which is explained by the diminishing QTM contribution. The appearance of multiple relaxation processes is also observed for higher x, which is explained as the creation of multiple, separate frequency domains, as a result of the competition between QTM and the direct process contributions. We present a thorough, systematic study of magnetic dilution, which will hopefully be useful to estimate optimal dilutions in similar solid solutions.
单离子磁体长期以来一直被认为是记录少量信息的良好潜在候选者。已知最小的单离子磁体之一是CoBr（吡啶）。这种分子化合物主要由于热激活的奥尔巴赫过程而表现出缓慢的磁化弛豫，[A.M.马杰尔等人，《化学科学》，2018年，9卷，7277 - 7286页]。然而，由于磁化过程的直接、拉曼和量子隧穿，在低温下总弛豫时间会显著缩短。在低温下，这种情况下可能的弛豫路径的概率分布有利于量子隧穿磁化（QTM）和直接过程，而不是奥尔巴赫过程。为了延长弛豫时间，该化合物用抗磁性的锌进行稀释，得到通式为CoZnBr（吡啶）（x = 0.91、0.67、0.43、0.24和0.06）的5种类似物，通过独立的实验技术（粉末X射线衍射、红外光谱）证实为固溶体。抗磁性锌离子的存在改变了材料中钴中心之间的偶极相互作用分布，这导致弛豫时间单调变化，随着稀释度增加弛豫时间变长，这可以用QTM贡献的减少来解释。对于更高的x值，还观察到多个弛豫过程的出现，这被解释为由于QTM和直接过程贡献之间的竞争而产生了多个独立的频域。我们对磁稀释进行了全面、系统的研究，希望这将有助于估计类似固溶体中的最佳稀释度。
