Crystal-field-driven magnetoelectric coupling in the non-Kramers hexaaluminate PrMgAl₁₁O₁₉

We report broadband dielectric spectra of the non-Kramers hexaaluminate PrMgAl₁₁O₁₉, revealing a pronounced interplay between permittivity and magnetization at cryogenic temperatures. The zero-field dielectric response follows a Barrett-type quantum-paraelectric form, while a broad dielectric anomaly near 5 K shows a complex field dependence that mirrors the multi-hump behavior of the magnetic specific heat, evidencing robust magnetoelectric coupling. The inverse permittivity ε′⁻¹ (T, H) scales linearly with M², consistent with a biquadratic P²M² term in a Landau framework. Fits yield a temperature-dependent coupling constant λ(T) that decreases with heating from (1.07 ± 0.01) × 10⁻⁴ μB⁻² (at 5 K) to (4.77 ± 0.02) × 10⁻⁵ μB⁻² (at 10 K), reflecting the thermal population of low-lying energy levels of Pr³ ⁺. Consistently, the uniaxial thermal expansion develops an additional low-temperature hump below ∼30 K that is progressively suppressed by magnetic field, recovering an approximately saturated response by 9 T. These results identify PrMgAl₁₁O₁₉ as a paradigmatic non-Kramers hexaaluminate where quantum paraelectricity and magnetoelectric interactions are intrinsically entangled, establishing hexaaluminates as a tunable platform for magnetoelectric physics in frustrated quantum materials.