Raman Sankar's Website

Multistage development of anisotropic magnetic correlations in the Co-based honeycomb lattice Na₂Co₂TeO₆

Dr Raman Sankar and Dr K.Y. Choi investigate the magnetic and thermal evolution of magnetic correlations for Co-based honeycomb lattice Na₂Co₂TeO₆ with ²³Na nuclear magnetic resonance and static magnetic susceptibility χ (T). The studied compound shows three-dimensional (3D) long-range magnetic ordering at T_N = 26 K. On cooling through T∗ ≈ 110 K, a simple paramagnetic state undergoes a crossover to a correlated paramagnetic state featuring a power-law dependence of the nuclear spin-lattice (1/T₁) and spin-spin (1/T₂) relaxation rates as well as of the out-of-plane χ(T ). The magnetic-field-direction dependence of 1/T₁, 1/T₂, and χ(T ) uncovers anisotropic spin-spin correlations of a two-dimensional (2D) renormalized classical character. In a magnetically ordered state, we are able to identify four successive transitions or crossovers occurring at T_N = 26, T_N1 = 16, T_N2 = 7, and T_N3 = 3.5 K. The multiple transitions and crossovers are associated with the coexistence of 2D and 3D magnetic orders or reorientation of the ordered spins. Our results suggest the presence of various types of frustrating interactions and their energy hierarchy that control complex magnetic structures and anisotropic magnetism.