Sc2Ga2CuO7: A possible quantum spin liquid near the percolation threshold

Abstract

Sc2Ga2CuO7 (SGCO) crystallizes in a hexagonal structure (space group: P63/mmc), which can be seen as an alternating
stacking of single and double triangular layers. Combining neutron, x-ray, and resonant x-ray diffraction we establish that
the single triangular layers are mainly populated by non-magnetic Ga3+ ions (85% Ga and 15% Cu), while the bi-layers have comparable population of Cu2+ and Ga3+ ions (43% Cu and 57% Ga). Our susceptibility measurements in the temperature range 1.8 - 400 K give no indication of any spin-freezing or magnetic long-range order (LRO).We infer an effective paramagnetic moment μeff = 1.79±0.09 μB and a Curie-Weiss temperature �CW of about −44 K, suggesting antiferromagnetic interactions between the Cu2+(S = 1/2) ions. Low-temperature neutron powder diffraction data showed no evidence for LRO down to 1.5
K. In our specific heat data as well, no anomalies were found down to 0.35 K, in the field range 0-140 kOe. The magnetic
specific heat, Cm, exhibits a broad maximum at around 2.5 K followed by a nearly power law Cm/ T� behavior at lower
temperatures, with � increasing from 0.3 to 1.9 as a function of field for fields upto 90 kOe and then remaining at 1.9 for fields
upto 140 kOe. Our results point to a disordered ground state in SGCO.