Anisotropic magnetodielectric coupling in layered antiferromagnetic FePS3

We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic ${\mathrm{FePS}}₃$ (N\'eel temperature ${T}_N\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 120 K) with perpendicular anisotropy. Above ${T}_N$, while the dielectric response function along the $c$ axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies.