Spiral magnetic phase in Li-doped Na2IrO3

The doping of the honeycomb lattice compound Na2IrO3 with cations having smaller ionic radius such as lithium was supposed to drive the system into a Kitaev spin liquid phase. Even at the smallest doping level the long range magnetic order, present in the parent compound, got suppressed as evidenced by susceptibility and heat capacity measurements. At low doping levels, the long range ordered magnetic phase is accompanied by the formation of a glassy state with a transition temperature of T-F similar to 5 K as determined by dc and ac magnetic susceptibility. The magnetic excitation spectrum, measured by inelastic neutron scattering, shows a significant change with doping. Our inelastic neutron scattering data can be well described by linear spin wave theory, revealing the formation of a spiral magnetic phase.