Novel spin-liquid behaviour in some Ir-based oxide systems*

The 5d-transition metal based oxide systems are of current interest due to the prominence of spin-orbit coupling driving them to a Mott insulating state in spite of a small Coulomb repulsion energy U. We have recently investigated Ba3IrTi2O9 and Ba3YIr2O9 systems (with hexagonal arrangement of Ir) using x-ray diffraction, magnetization, heat capacity, and NMR. With a power-law temperature dependence of the low-T magnetic heat capacity, we find evidence of spin-liquid behavior in the former. Whereas the latter is magnetically long-range ordered below 4 K, it transforms to a cubic structure when reacted at 1273 K under a pressure of 8GPa. The high-pressure (HP) prepared sample, though with semiconductor-like resistivity, has (in addition to the phonon term) a T-linear heat capacity term with $\gamma$ = 10 mJ/mol K$^2$ and a T-linear $^{89}$Y NMR spin-lattice relaxation rate. We conclude that the HP phase exhibits spin-liquid behavior.