  Ag2CrO2 is an S=3/2 frustrated triangular lattice antiferromagnet without
orbital degree of freedom. With decreasing temperature, a 4-sublatice spin
state develops. However, a long-range partially disordered state with 5
sublattices abruptly appears at TN=24 K, accompanied by a structural
distortion, and persists at least down to 2 K. The spin-lattice coupling
stabilizes the anomalous state, which is expected to appear only in limited
ranges of further-neighbor interactions and temperature. It was found that the
spin-lattice coupling is a common feature in triangular lattice
antiferromagnets with multiple-sublattice spin states, since the triangular
lattice is elastic.
