Critical Slowing Down of Triangular Lattice Spin-3/2 Heisenberg Antiferromagnet Li₇RuO₆ via ⁷Li NMR

抄録

We report on ⁷Li NMR studies of single crystals of the triangular-lattice Heisenberg antiferromagnet Li₇RuO₆. A slow critical divergence with a wide critical region of |T⁄T_N−1|≤7 was observed in ⁷Li nuclear spin–lattice relaxation rate. The slowing down of staggered spin fluctuations was analyzed in a renormalized classical region of a two-dimensional triangular-lattice nonlinear sigma model. Spin stiffness constant was found to decrease to about 20% of its value in spin-wave approximation. The effect of spin frustration, e.g., Z₂ vortex excitations on critical phenomena, is suggested.