Two-dimensional honeycomb magnets with low coordination numbers provide an ideal framework for investigating the interplay between lattice geometry, reduced dimensionality, and magnetic interactions. While low-spin honeycomb systems have been extensively studied, high-spin counterparts remain comparatively unexplored, despite their importance for understanding the classical limit of magnetism. In this work, we present a comprehensive investigation of ${\mathrm{SrFeSnP}}_3{\mathrm{O}}_{12}$, a two-dimensional (2D) honeycomb lattice compound in which ${\mathrm{Fe}}^{3+}$ ions ($S=5/2$) form a well-defined magnetic network. Magnetic susceptibility measurements reveal a transition at $T_N=13\mathrm{K}$, signaling the onset of long-range antiferromagnetic order, which is further supported by heat capacity measurements. Nuclear magnetic resonance (NMR) measurements confirm the development of internal magnetic fields below $T_N$, while the sublinear temperature dependence of the spin-lattice relaxation rate above $T_N$ provides evidence for short-range spin correlations in the paramagnetic regime. Electron spin resonance measurements reveal a single isotropic resonance at high temperatures, indicating isotropic spin correlations within the 2D honeycomb lattice. Theoretical calculations of symmetric exchange interactions show that the nearest-neighbor in-plane exchange interaction $J_1$ is the dominant one and antiferromagnetic in nature. Our computed $\text{Fe-}d$ Wannier functions show that the interaction is mediated via Fe–O–P–O–Fe superexchange pathway. Our calculation in the presence of spin-orbit coupling shows that the system has negligible magnetic anisotropy, suggesting an isotropic 2D Heisenberg spin model relevant for the system. Local probe measurements, such as electron spin resonance and NMR, together with specific heat data, indicate the development of short-range antiferromagnetic correlations that persist well above the long-range ordering temperature. These results establish ${\mathrm{SrFeSnP}}_3{\mathrm{O}}_{12}$ as a model high-spin honeycomb magnet bridging the classical and quantum regimes of magnetism.

Close

PrevNext

View figure in article

• Density of states
• Electronic structure
• Entropy
• Magnetic interactions
• Magnetic phase transitions
• Magnetic susceptibility
• Magnetism
• Specific heat
• Spin-orbit coupling
• Nuclear magnetic resonance