Investigation of the ground-state magnetic structure of a novel triangular-lattice antiferromagnet Na2SrCo(PO4)2

Recently, Na2SrCo(PO4)2 (NSCPO), a novel spin-1/2 triangular-lattice antiferromagnet (TLAF) with a monoclinically distorted structure and an antiferromagnetic order at 600 mK, is synthesized. Due to the distortion of the in-plane triangular lattice and its low crystallographic symmetry, the off-diagonal symmetric exchange interaction, pseudo-dipolar exchange interaction and Dzyaloshinskii-Moriya interaction are found to be all present, in addition to the dominant Heisenberg XXZ model. This is in stark contrast to other triangular-lattice cobaltates, which are all nearly ideal Heisenberg TLAFs well described by the XXZ model alone. NSCPO, therefore, is a rare example in the triangular-lattice cobaltates showing a significant magnetic anisotropy and call for more attentions. Based on the microscopic model description of this material with realistic model parameters, the ground-state magnetic structure of NSCPO is calculated by density matrix renormalization group (DMRG) method. A stripe-like order with k= (1/2, 1/2, 0) is predicted as its magnetic ground state, awaiting the experimental verification. We propose to perform neutron powder diffraction experiment on NSCPO to verify the theoretical prediction and the correctness of the model parameters.