A detailed study of the structural and magnetic properties of a spin-5/2 triangular lattice antiferromagnet RbFe(HPO3)2 is presented using x-ray diffraction, magnetization, heat capacity, and 31P nuclear magnetic resonance (NMR) experiments on a polycrystalline sample. The crystal structure features an equilateral triangular lattice of Fe3+ ions. The thermodynamic measurements reveal the onset of a magnetic long-range order at TN1≃7.8 K in zero-field, followed by another low temperature field induced ordering at TN2 in higher fields. The transition at TN1 is further confirmed from the NMR spin lattice relaxation measurements. The value of the frustration ratio (f≃7) implies moderate spin frustration in the compound. The 31P NMR spectra exhibit two distinct spectral lines corresponding to two inequivalent phosphorus sites (P1 and P2), consistent with the crystal structure. The P1 site is strongly coupled with an isotropic hyperfine coupling of Ahfiso=0.55(2) T/μB while the P2 site is weakly coupled with Ahfiso=0.25(3) T/μB with the Fe3+ ions. The magnetic susceptibility and NMR shift data are described well assuming a spin-5/2 isotropic triangular lattice antiferromagnetic model with an average exchange coupling of J/kB=2.8(2) K. Below TN1, the spectra evolve into a nearly rectangular powder pattern, indicating a commensurate antiferromagnetic type order. The 31P spin-lattice relaxation rate well below TN1 follows a T3 temperature dependence, implying a two-magnon Raman scattering mechanism in the ordered state. Three well-defined phase regimes are clearly ascertained in the H−T phase diagram, reflecting a weak magnetic anisotropy in the compound.
@article{arxiv.2511.17480,
title = {Frustration driven magnetic correlations in the spin-$5/2$ triangular lattice antiferromagnet RbFe(HPO$_{3}$)$_{2}$},
author = {V. Nagpal and Sebin J. Sebastian and Surya P. Patra and S. Shibash and Q. -P. Ding and Y. Furukawa and R. Nath},
journal= {arXiv preprint arXiv:2511.17480},
year = {2025}
}