Ferromagnetic Short-Range Correlations in a Two-Dimensional Triangular Lattice Antiferromagnet with S=1/2 LiNiO₂

Abstract

We have demonstrated that a two-dimensional triangular lattice antiferromagnet with spin=1/2 LiNiO₂ reveals ferromagnetic short-range spin correlations in forward scattering below T_N1∼240 K, unlike other two-dimensional trianglar lattice antiferromagnets. The intensity of diffuse scattering in the forward direction appears below T_N1, and monotonically increases as the temperature is lowered, then shows a sharp divergence at T_N2∼35 K. The present results suggest that a frozen spin pattern with the ferromagnetic short-range correlation similar to the spin glass phase is realized at the low-temperature phase below T_N2. In contrast, no appreciable intensity was detected around the (1/3, 1/3, n) positions, being consistent with early studies.