Quantum Fluctuations in Magnetically Frustrated Gd2GaSbO7 and Gd2InSbO7 Pyrochlores
Gd2GaSbO7 and Gd2InSbO7 pyrochlore compounds exhibit quantum fluctuations in a spin ice-like state. These compounds have not been adequately studied based on the concept of magnetic frustration. Here, we have synthesised and characterised Gd2GaSbO7 and Gd2InSbO7 to investigate their ground-state magnetic properties. We confirmed the cubic pyrochlore structure via X-ray powder diffraction. Magnetic and heat capacity measurements show an absence of magnetic order down to 400 mK. Interestingly, the low-temperature magnetic heat capacity of Gd2GaSbO7 and Gd2InSbO7 exhibits a broad maximum around T_{\text{max}} = 0.9 K and T_{\text{max}} = 1 K, respectively. The low-temperature Cmag data fit with the power-law C_{\text{mag}} \approx T^{\frac{d}{n}} with dependencies of T^{1.71} for Gd2GaSbO7 and T^{1.49} for Gd2InSbO7, suggesting spin fluctuations caused by the disorder of magnetic moments at low temperatures. Both compounds retain residual entropy akin to water ice, resembling the spin ice state. Additionally, we analysed the ratio between nearest-neighbour exchange and dipolar interaction for all reported Gd-based pyrochlores, finding that Gd2InSbO7 has the lowest and weakest exchange interaction among them. This indicates that chemical pressure affects exchange interaction due to the different pathways of mediators between magnetic ions. This study reveals robust quantum fluctuations in the ground state in GGSO and GISO, similar to quantum spin ice compounds such as Pr2Zr2O7, Pr2Sn2O7, and Yb2GaSbO7. Other Gd-pyrochlore compounds exhibit long-range magnetic order, which is in stark contrast to this.