Non-technical abstract: Magnetic oxide compounds are often made with the magnetic constituent being drawn from the fourth row of the periodic table, from what is also referred to as the first transition series. The elements that one normally associates with magnets, such as iron, are also frequently the chief components of useful magnetic oxides. In recent years, there has been a growing recognition that developing new kinds of magnetic materials with elements that are not from the first transition series can be highly rewarding. With support of the Solid State and Materials Chemistry Program in the Division of Materials Research, this specific project focuses on one member of the second transition series, the element palladium. While making magnetic oxides of palladium is highly challenging for a number of technical reasons, the results can be deeply interesting, both from the fundamental science perspective as well as new applications. The nature of magnetism that these new materials display changes a lot of the current thinking on magnetic behavior, and allows for new directions in magnetic technologies to be opened up. These include applications in magnetic data storage, novel approaches to magnetic switching, and new generations of magnets for high-efficiency electric motors and wind turbines.
The problem addressed in the project is in regard to functional complex oxide compounds containing divalent palladium ions: Can this class of materials be significantly expanded, from the few, rare example that are known. The goals of the project are to develop more examples of magnetic and magnetodielectric oxide compounds of palladium, and separately, achieve compositional tuning of palladium compounds across non-metal-to-metal transitions. Two major challenges need to be overcome to achieve the stated goals, associated with the oxophobic nature of palladium and the very strong tendency of palladium ions to adopt the diamagnetic, square-planar configuration associated with 8 d electrons. The first is simply the difficulty of preparing and stabilizing oxides containing divalent palladium. Indeed, any effort in this direction would add to a comparatively small inventory. The second challenge associated with preparing magnetic palladium oxides is to induce divalent palladium ions to adopt the kinds of polyhedral coordination that would result in unpaired spins. The proposed solutions to the challenge of stabilizing palladium ions in oxides include understanding and employing inductive effects of electropositive cations to expand the number of known complex palladium oxides. Electropositive cations "soften" oxygen, and result in stable palladium oxides with significantly covalent palladium-to-oxygen interactions. The methods employed for the project will include the use of first-principles calculations on bulk structures and slab models, carried out concurrently with experimental efforts, to aid in understanding such inductive stabilization. The use of microwave heating techniques will aid in the rapid preparation of new compounds at low enough temperatures that auto-reduction to Pd metal is avoided. The activity will expand the domain, and enhance understanding of the materials chemistry and physics of functional palladium oxides, and will inform 4d magnetism. Insulating 4d magnets have higher ordering temperatures than their 3d counterparts and are promising for applications including as novel magnetodielectric materials with relatively high magnetic ordering temperatures.
