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

稀土离子具有大量的未成对电子（Eu ~（2+）/Gd ~（3+）/Tb ~（4+）可达7个）、较大的磁矩（Dy ~（3+）和Ho ~（3+）可达~11 Bohr磁子）和较强的自旋轨道耦合。因此，它们构成了永久磁铁和分子磁铁以及自旋电子学应用的有吸引力的构建块。然而，相邻的Ln 3+阳离子之间的超交换相互作用通常非常弱，这是4f态的准核心性质及其与桥接配体的价函数相当差的重叠的结果。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磁有序通常仅在低温下（大多低于10 K）实现。在目前的项目中，我们试图通过在晶格中引入Ag 2+中心来强烈增强离散和扩展的镧系亚晶格的体磁极化。在4d 9构型下，Ag 2+阳离子有一个未配对的d电子;在d10组中的空穴具有高达11 eV的极大电子亲合势，因此它与相邻配体的价轨道显着杂交。因此，Ag 2+阳离子即使在氟化物配体（通常认为其与过渡金属形成离子键）处也会引入强自旋极化，而Ag 2+离子则会在离子交换中引入强自旋极化。- - Ag ~（2+）超交换超过100 meV。计算结果表明，自旋极化甚至会影响从Ag 2+网站放置几埃的闭壳阳离子。在铁磁耦合系统中，自由自旋超过0.1Bohr的磁子位于F-中心。该方案的核心创新点，即使用Ag ~（2+）阳离子作为自旋超极化器，将通过一系列新的基于Ln-Ag ~（2+）氟化物的化合物进行探索，这些化合物将通过全面的结构、光谱和磁化学方法进行表征。我们预计，Ag 2+和Ln 3+网站之间的磁超交换将是实质性的，允许在接近室温的温度下的长程磁序。我们还将探索将这些概念转化为低维或分子状Ln-Ag 2+物种的可能性。这将使进一步的结构和性能工程的自旋器件在环境条件下操作的应用。

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.