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

We have demonstrated that a two-dimensional triangular lattice antiferromagnet with spin=1/2 LiNiO 2 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.