title: Pressure and strain effects of hexagonal rare-earth manganites: a first-principles study.
abstract: We have investigated the structural, electrical and magnetic properties as well as the phonon modes of hexagonal rare-earth manganites (RMnO3, R  =  Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) under chemical pressure, hydrostatic pressure and epitaxial strain by first-principles calculations. The magnetic ground state of RMnO3 is found to have Γ4 magnetic configuration and to be stable under all considered external conditions. In contrast, the K3 phonon mode, which is the primary order parameter and responsible for the 'improper ferroelectricity', is greatly influenced by pressure and epitaxial strain. Consequently, the electric polarization is enhanced by 56.7% when the chemical pressure increases from R  =  Pr to R  =  Lu. The hydrostatic pressure can also improve the polarization to a certain degree, e.g. by 14.7% from 0 GPa to 40 GPa in LuMnO3. Finally, the dependence of polarization on the epitaxial strain is also given, revealing that the compressive strain could promote the ferroelectricity while tensile strain will suppress it.
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics and Collaborative Innovation Center of Quantum Matter, Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China.
authors.forename: Hengxin
authors.initials: H
authors.lastname: Tan
authors.forename: Changsong
authors.initials: C
authors.lastname: Xu
authors.forename: Menglei
authors.initials: M
authors.lastname: Li
authors.forename: Shanying
authors.initials: S
authors.lastname: Wang
authors.forename: Bing-Lin
authors.initials: BL
authors.lastname: Gu
authors.forename: Wenhui
authors.initials: W
authors.lastname: Duan