Interacting nanoscale magnetic superatom cluster arrays in molybdenum oxide bronzes.

In this study, we examine several reduced ternary molybdates in the family of yellow rare earth molybdenum bronzes produced by electrochemical synthesis with composition LnMo16O44. These compounds contain an array of electrically isolated but magnetically interacting multi-atom clusters with composition Mo8O36. These arrayed superatom clusters support a single hole shared among the eight molybdenum atoms in the unit, corresponding to a net spin moment of 1µB, and exhibit magnetic exchange between the units via the MoO4 tetrahedra (containing Mo6+ ions) and the LnO8 cubes (containing Ln3+ ions). The findings presented here expand on the physics of the unusual collective properties of multi-atom clusters and extend the discussion of such assemblages to the rich structural chemistry of molybdenum bronzes.

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.