POL-LAN-DE - Enhancement of magnetic interactions in lanthanide compounds using Ag(II) as spin super-polarizer

稀土(Ln)离子具有大量未成对电子(Eu2+/Gd3+/Tb4+高达7个)，大磁矩(Dy3+和Ho3+高达~11玻尔磁子)和强的自旋-轨道耦合。因此，它们构成了永久磁体和分子磁体以及自旋电子学应用的有吸引力的积木。然而，相邻的Ln3+离子之间的超交换作用一般很弱，这是由于4f态的准核心性质以及它们与桥联配体的价函数的较差重叠的结果。反过来，大多数基于Ln(n+)的化合物表现出有趣的，有时甚至是奇异的磁性；然而，3D磁性有序通常只在低温下(大多低于10K)才能实现。在本项目中，我们试图通过在晶格中引入Ag2+中心来增强离散的和扩展的稀土亚晶格的体磁极化。具有4D9构型的AG2+有一个未配对的d电子；D10中的空穴具有高达11 eV的极大的电子亲和力，因此它与邻近配体的价轨道发生了显著的杂化。因此，当Ag2+...F-...Ag2+的超交换超过100 meV时，即使在氟化物配体(通常认为这些配体形成与过渡金属的离子键)上，Ag2+离子也会引入强烈的自旋极化。计算表明，即使在离AG2+位置几埃的位置上，自旋极化也会影响闭壳型阳离子。在铁磁耦合系统中，自由自旋超过0.1玻尔磁子位于F中心。这一提议的核心创新，即使用Ag2+阳离子作为自旋超极化器，将通过一系列新的Ln-Ag2+氟化物化合物来探索，这些化合物将通过综合的结构、光谱和磁化学方法进行表征。我们预计，Ag2+和Ln3+之间的磁性超交换将是实质性的，从而允许在接近室温的温度下实现长范围的磁有序。我们还将探索将这些概念转化为低维或类似分子的Ln-AG2+物种的可能性。这将使在环境条件下运行的旋转设备中的应用能够进一步进行结构和性能工程。

Lanthanide (Ln) cations are characterized by large number of unpaired electrons (up to 7 for Eu2+/Gd3+/Tb4+), large magnetic moments ranging up to ~11 Bohr magneton in the case of Dy3+ and Ho3+, and strong spin-orbit coupling. As such, they constitute attractive building blocks for permanent as well as molecular magnets and for spintronics applications. However, superexchange interactions between the neighboring Ln3+ cations generally are very weak, a consequence of the quasi-core nature of the 4f states and their rather poor overlap with the valence functions of the bridging ligands. In turn, most Ln(n+)-based compounds exhibit interesting and sometimes even exotic magnetic properties; however, 3D magnetic ordering is usually achieved only at low temperatures (mostly below 10 K). In the current project, we seek to strongly enhance the bulk magnetic polarization of discrete and extended lanthanide sublattices via introduction of Ag2+ centers into the crystal lattice. With their 4d9 configuration, Ag2+ cations have one unpaired d electron; the hole in the d10 set has an extremely large electron affinity up to 11 eV, hence it hybridizes markedly with the valence orbitals of neighboring ligands. In consequence, Ag2+ cations introduce strong spin polarization even at fluoride ligands (which are commonly believed to form ionic bonds to transition metals) while the Ag2+...F-...Ag2+ superexchange exceeds 100 meV. Calculations show that spin polarization affects even closed-shell cations placed several angstrom from the Ag2+ site. In ferromagnetically coupled systems a free spin exceeding 0.1 Bohr magneton resides on a F- center.The central innovation of this proposal, i.e. the use of Ag2+ cations as spin super-polarizers, will be explored via a range of new Ln-Ag2+ fluoride-based compounds that will be characterized by comprehensive structural, spectroscopic and magnetochemical methods. We anticipate that the magnetic superexchange between Ag2+ and Ln3+ sites will be substantial, allowing for long-range magnetic order at temperatures approaching room temperature. We will also explore possibilities to translate these concepts into low-dimensional or molecule-like Ln-Ag2+ species. This would enable further structure and property engineering for applications in spin devices operating at ambient conditions.