${\mathrm{Sc}}_2{\mathrm{Ga}}_2{\mathrm{CuO}}_7$ (SGCO) crystallizes in a hexagonal structure (space group: $P{6}_3/mmc)$, 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 nonmagnetic ${\mathrm{Ga}}^{3+}$ ions (85% Ga and 15% Cu), while the bilayers have comparable population of ${\mathrm{Cu}}^{2+}$ and ${\mathrm{Ga}}^{3+}$ 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 ${\mu }_{\mathrm{eff}}=1.79\pm 0.09{\mu }_B$ and a Curie-Weiss temperature ${\theta }_{\mathrm{CW}}$ of about $-44$ K, suggesting antiferromagnetic interactions between the ${\mathrm{Cu}}^{2+}(S=1/2)$ 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 $C_m$, exhibits a broad maximum at around 2.5 K followed by a nearly power law $C_m\propto T^{\alpha }$ behavior at lower temperatures, with $\alpha$ increasing from 0.3 to 1.9 as a function of field for fields up to 90 kOe and then remaining at 1.9 for fields up to 140 kOe. Our results point to a disordered ground state in SGCO.

• Received 16 June 2015
• Revised 3 November 2015

DOI:https://doi.org/10.1103/PhysRevB.92.180411