BSc defense for Bastian Lau Holten-Møller

Titel:  An investigation of the solid solution Ba₃NiNb₂₋ₓSbₓO₉ and the identification of an S = 1 quantum spin liquid candidate.

Abstract: Certain nickel-based hexagonal perovskites have been shown to form frustrated spin systems and may exhibit even more exotic magnetic behavior. This project investigates a class of triple perovskites: Ba₃NiNb₂₋ₓSbₓO₉. A solid solution of these compounds was synthesized as powder and analyzed by X-ray diffraction.

Several compositions were deemed to be phase-pure, while others were identified as mixtures of pure phases. One composition in particular, Ba₃NiNbSb₁.₅O₉ , was identified as especially interesting due to its structural similarity to a known quantum spin liquid candidate, a high-pressure phase of Ba₃NiSb₂O₉. 

This sample was further characterized using electron diffraction to determine its structure, and with a SQUID magnetometer to probe its magnetic properties. We find the structure to be similar to the high-pressure Ba₃NiSb₂O₉, although not definitively the same.

We also observe a lack of magnetic ordering, indicating a frustration factor of at least 20, which is consistent with a highly frustrated magnetic system, but is not as high as expected of a quantum spin liquid.

For a more conclusive determination, both further structural- and magnetic characterization is desirable. 

Supervisor: Kim Lefmann

Censor: Jørn Bindslev Hansen (DTU)