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arXiv · 2507.01403

Magnetic Ground State and Spin Excitations in the 2D Trimerized Collinear-II Lattice Antiferromagnet Li2Ni3P4O14

K. S. Chikara·A. K. Bera·A. Kumar·S. M. Yusuf·F. Orlandi·C. Balz
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Abstract

We report the magnetic ground state, spin excitations, and spin Hamiltonian of the 2D spin-1 trimerized Heisenberg antiferromagnet Li2Ni3P4O14. Below the magnetic ordering temperature TN = 14.5 K, the compound exhibits a canted long-range antiferromagnetic order with a propagation vector k = (0 0 0), consistent with the magnetic space group P21/c.1 (No. 14.75). The ground state magnetic structure consists of ferromagnetic spin-trimers of Ni2+ ions. The spin-trimers are coupled antiferromagnetically along the c-axis and ferromagnetically along the a-axis. Inelastic neutron scattering (INS) reveals gapped and dispersive magnon excitations below the TN, and gapless quasi-elastic scatterings at higher temperature. The linear spin-wave theory simulations reveal the essential features of the excitation spectrum; by a spin Hamiltonian composed of ferromagnetic intra-trimer exchange interaction J1 and inter-trimer exchange interactions J2 (FM) and J3(AFM) within the bc plane. The J2 and J3 along the b-axis and c-axis, respectively, with strengths of J2/J1=0.79 and J3/J1=-0.91. In addition, a weak inter planer ferromagnetic exchange interaction J4 (|J4/J1|~0.12) is found along the a-axis. The determined exchange constants reveal a 2D trimerized Collinear-II spin lattice within the bc-plane. The analysis of INS spectra by linear spin-wave theory also yields a moderate single-ion anisotropy (D/J1=0.48) which accounts for the observed spin gap below TN as well as the metamagnetic transition near 44 kOe in dc magnetization (M vs H) curves. These findings identify Li2Ni3P4O14 as a rare realization of a two-dimensional trimerized spin system and offer the direct experimental confirmation of theoretically predicted magnon excitations, unveiling the fundamental characteristics of the expected excitation spectrum.

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K. S. Chikara, A. K. Bera, A. Kumar, S. M. Yusuf, F. Orlandi, C. Balz. 2025-07-02. Magnetic Ground State and Spin Excitations in the 2D Trimerized Collinear-II Lattice Antiferromagnet Li2Ni3P4O14. https://doi.org/10.1103/8jpn-h83f

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