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

• Applicant: Professor Dr. Paul Kögerler
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 380626961

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.

• DFG Programme: Research Grants
• International Connection: Poland
• Cooperation Partner: Professor Dr. Wojciech Grochala