Crystal-Field--Driven Magnetoelectric Coupling in the Non-Kramers Hexaaluminate PrMgAl11O19

TL;DR

The paper investigates magnetoelectric coupling in PrMgAl11O19, a non-Kramers hexaaluminate with a Pr3+ quasi-doublet. Dielectric spectroscopy reveals a Barrett-type quantum paraelectric response in zero field and a field-tunable low-temperature dielectric anomaly linked to crystal-field excitations, evidencing magnetoelectric coupling. The inverse permittivity scales linearly with the square of the magnetization, consistent with a biquadratic ME term $P^{2} M^{2}$, from which a temperature-dependent coupling $\lambda(T)$ is extracted and found to decrease with heating as low-energy CF levels populate. A transverse-field Ising model for the Pr quasi-doublet provides a microscopic basis for the biquadratic channel, with potential cubic contributions via local distortions; overall, PrMgAl11O19 emerges as a tunable platform to study magnetoelectricity in frustrated quantum paraelectrics.

Abstract

We report broadband dielectric spectra of the non-Kramers hexaaluminate PrMgAl(*{11})O(*{19}), 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 shifts systematically to higher temperatures under applied magnetic fields, evidencing robust magnetoelectric coupling. The inverse permittivity (\varepsilon'^{-1}(T,H)) scales linearly with (M^{2}), consistent with a biquadratic (P^{2}M^{2}) term in a Landau framework. Fits yield temperature-dependent coupling constants (λ(T)) that decrease with heating, reflecting the thermal population of low-lying energy levels of Pr(^{3+}). These results identify PrMgAl(*{11})O(*{19}) 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.

Figures (2)

• Figure 1: (a) Zero-field dielectric permittivity $\varepsilon'(T)$ with Barrett fit (solid red line) from 10–170 K. (b) Temperature-dependent dielectric permittivity $\varepsilon'(T,H)$ measured at 64 kHz and different magnetic fields. (c) Isothermal magnetization $M(H)$ at 5 and 10 K for fields applied along the $c$ axis and in the $ab$ plane, highlighting strong Ising anisotropy.
• Figure 2: (a) Inverse permittivity $\varepsilon'^{-1}$ versus $M^{2}$ at 5 K. Solid line: linear fit yielding $\lambda_{5\,\mathrm{K}}$. (b) Linear scaling of $\varepsilon'^{-1}$ with $M^{2}$ at 10 K, giving $\lambda_{10\,\mathrm{K}}$.