Effects of biaxial strain on the improper multiferroicity inh−LuFeO3films studied using the restrained thermal expansion method

Abstract

Elastic strain is potentially an important approach in tuning the properties of the improperly multiferroic hexagonal ferrites, the details of which have however been elusive due to the experimental difficulties. Employing the method of restrained thermal expansion, we have studied the effect of isothermal biaxial strain in the basal plane of h-LuFeO3 (001) films. The results indicate that a compressive biaxial strain significantly enhances the ferrodistortion, and the effect is larger at higher temperatures. The compressive biaxial strain and the enhanced ferrodistortion together, cause an increase in the electric polarization and a reduction in the canting of the weak ferromagnetic moments in h-LuFeO3, according to our first principle calculations. These findings are important for understanding the strain effect as well as the coupling between the lattice and the improper multiferroicity in h-LuFeO3. The experimental elucidation of the strain effect in h-LuFeO3 films also suggests that the restrained thermal expansion can be a viable method to unravel the strain effect in many other epitaxial thin film materials.

Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3

“…16 Due to the size difference of Lu 3+ and Yb 3+ , 14 the lattice constant of the basal plane of h-LuFeO3 is smaller than that of h-YbFeO3: a = 5.963 Å for h-LuFeO3 and a = 6.021 Å for h-YbFeO3. 31 Our recent work suggests that a compressive biaxial strain may reduce the canting of the Fe moments in h-REFeO3, 50 which is in line with the correlation between the lattice constant and weak ferromagnetic moment on Fe observed here.…”

Polyhedron and Charge Ordering in Interfacial Reconstruction of a Hexagonal Ferrite/Sapphire Heterostructure

“…Here, we perform a comprehensive analysis of the interfacial reconstruction at a heterostructure combined with hexagonal ferrite and sapphire, whose lattice mismatch is almost 20%. The model system is hexagonal LuFeO 3 ( h -LuFeO 3 ), an important branch of hexagonal multiferroics, which has attracted much attention because of its improper ferroelectricity at room temperature, the weak ferromagnetism induced by Dzyaloshinskii–Moriya (DM) interactions, and the magnetoelectric effect based on the strong lattice–spin coupling. − For h -LuFeO 3 ( P 6 3 cm , a = b = 5.9642 Å, c = 13.12607 Å, Figure a), it is separated by [LuO 2 ] and [FeO] layers along the c axis, where the closest coordinations between Lu–O and Fe–O are a distorted octahedron and a bipyramid, respectively. The trimerization of the FeO 5 bipyramid elicits the movement of Lu along the c axis, inducing the geometric ferroelectricity.…”

Real-Space Infrared Spectroscopy of Ferroelectric Domain Walls in Multiferroic h-(Lu,Sc)FeO3

“…22 LuFeO 3 normally hosts an orthorhombic structure, although the pure hexagonal phase can be stabilized under epitaxial strain. 23 Similarly, A-site substitution with Sc, the smallest and lightest of the Group III elements, leads to a more compact lattice, which favors the hexagonal structure (Figure 1a). This is due to chemical pressure effects, which give rise to local strain.…”

“…Ferrites generally adopt either an orthorhombic or hexagonal crystal symmetry depending on the radius of the A -site ion . LuFeO 3 normally hosts an orthorhombic structure, although the pure hexagonal phase can be stabilized under epitaxial strain . Similarly, A -site substitution with Sc, the smallest and lightest of the Group III elements, leads to a more compact lattice, which favors the hexagonal structure (Figure a).…”