Experimental Studies of Triangular Lattice Antiferromagnets with<i>S</i>=1/2: NaTiO₂and LiNiO₂

Abstract

Real triangular lattice antiferromagnet with S =1/2 has been long-awaited since Anderson pointed out that its ground state might be a quantum liquid-like state rather than the Néel state. In this paper we report that NaTiO 2 and LiNiO 2 are promising candidates for it, the former being near Heisenberg-type and the latter near Ising-type. Our magnetization measurements on LiNiO 2 show a striking linear to nonlinear response transition at T N1 =210 K. A pronounced anomaly appears in ESR at another transition T N2 =∼20 K suggesting a ferrimagnet-like ordered state below. However, neither ferromagnetic nor antiferromagnetic reflections could be observed in zero field neutron scattering between 1.4 and 300 K. The susceptibility of NaTiO 2 is low suggesting a strong antiferromagnetic coupling between the spins but no Brass scattering could be observed at 1.4 K. These are suggestive of the remarkable quantum effects.