Low temperature muSR study of a cation ordered quantum spin liquid

Honeycomb lattices of magnetic cations can be generated within the cubic ABO3 perovskite structure by alternating one layer of non-magnetic cations and two layers of magnetic ions in the cubic-[111] direction giving rise to A3BB’2O9 materials with the trigonal P-3m1 3C1:2 (Ba3SrTa2O9-type) structure. We are exploring 3C1:2-Ba3CaRu2O9 made by pressure transformation of a 6H precursor. Magnetic and heat capacity measurements show strong evidence for QSL behaviour with no magnetic transitions down to 50 mK despite a Weiss temperature ~ -35 K. Powder neutron diffraction data (collected recently from WISH, RB2220036) confirm that no magnetic ordering or structural phase transition occurs down to 1.5 K. Given the low magnetic moment (μeff = 1 μB) and the disordered, most likely dynamic nature of the ground state, muon spin relaxation (μSR) is an ideal tool to further investigate the magnetic properties. The EMU spectrometer will be needed in fly past mode as the sample is small and we request 3 days to study the muon spin relaxation in zero field as well as at a few applied longitudinal fields. We will perform a detailed temperature dependence scan of the relaxation rate down to the lowest measurable temperatures with a dilution refrigerator. The results from this experiment are necessary in order to clarify our previous results and to strengthen our understanding of the magnetic ground state of this novel QSL candidate material.