Effect of magnesium doping on the orbital and magnetic order in LiNiO(2)

In LiNiO2, the Ni3+ ions, with S=1/2 and twofold orbital degeneracy, are arranged on a triangular lattice. Using muon-spin relaxation and electron-spin resonance (ESR), we show that magnesium doping does not stabilize any magnetic or orbital order despite the absence of interplane Ni2+. A disordered, slowly fluctuating state develops below 12 K. In addition, we find that magnons are excited on the time scale of the ESR experiment. At the same time, a g factor anisotropy is observed, in agreement with | 3 z2 - r2 orbital occupancy. © 2008 The American Physical Society