Dzyaloshinskii – Moriya interaction, epitaxial strains, phase transitions in multiferroics with cycloidal structure

Abstract

In this paper, we explore magnetic phases and spin reorientation phase transitions (SRPT) in the BiFeO3 – like multiferroics. We consider the Dzyaloshinskii – Moriya exchange interaction (DMI) as the principle mechanism responsible for appearance of spin space modulated structures (SSMS) in BiFeO3 and focus the peculiar features of the DMI manifestation in single crystals and films. As an example we take a (110) – oriented BiFeO3 film whose thickness is much lower than the period of SSMS (dfilm≪λ) and construct phase diagram in terms “magnetic field H – perpendicular magnetic anisotropy (PMA) constant κ” accounting the PMA dependence on the strains, where the tensile strains correspond to the situation κ > 0; the compressive strains correspond to the situation κ < 0. Our findings shows that at the condition (dfilm≪λ) the SSMS modulated along the [001] axis with spin rotating in a plane (110) exists as the ground magnetic state in a definite range of the control parameters (H, ±κ). We show that magnetic field applied along the normal to the film along with strains leads to the transition into homogeneous magnetic state of the “easy plane” type at κ > 0 and tilted phase at κ < 0. As well as in the single crystals at the positive values κ > 0 phase transition from SSMS into homogeneous “easy plane” phase goes through the cone SSMS whose existence was recently experimentally confirmed [S. Kawachi, et al, Phys. Rev. Mater. 1, 024, 408 (2017)]. We believe that our findings performed for the (110) BiFeO3 film will be of interest for further experimental and theoretical research and the implementations of BiFeO3 based technologies.