Enhancing the Néel Temperature of h -LuFeO3 Thin Films to 200 K by Substrate-Induced Strain

Hexagonal lutetium ferrite (h-LuFeO3) is a promising multiferroic material, but its low Néel temperature (TN ≈ 130 K) limits its room-temperature applications. Herein, we demonstrate that epitaxial strain engineering enables robust tuning of its structural, ferroelectric, and magnetic properties. High-quality h-LuFeO3 thin films were epitaxially grown on yttria-stabilized zirconia (YSZ) (111) and Al2O3 (0001) substrates, introducing tensile and compressive strain, respectively. Atomic-scale scanning transmission electron microscopy analysis reveals that tensile strain reduces the c/a ratio of the h-LuFeO3 crystal lattice, while compressive strain increases the c/a ratio. Combined first-principles calculations and Monte Carlo simulations elucidate that tensile strain weakens the antiferromagnetic exchange interaction, lowering TN to approximately 50 K, whereas compressive strain strengthens the exchange coupling, raising TN to approximately 200 K. The strain-induced variation of TN follows a linear correlation with the c/a ratio. These results establish the c/a ratio as a quantitative structural descriptor, demonstrating that strain engineering is a powerful strategy to tailor the multiferroic properties of h-LuFeO3, with compressive strain offering a promising route toward room-temperature multiferroic applications.