Abstract
A current challenge in the field of magnetoelectric multiferroics is to identify systems that allow a controlled tuning of states displaying distinct magnetoelectric responses. Here we show that the multiferroic ground state of the archetypal multiferroic TbMnO3 is dramatically modified by epitaxial strain. Neutron diffraction reveals that in highly strained films the magnetic order changes from the bulk-like incommensurate bc-cycloidal structure to commensurate magnetic order. Concomitant with the modification of the magnetic ground state, optical second-harmonic generation (SHG) and electric measurements show an enormous increase of the ferroelectric polarization, and a change in its direction from along the c- to the a-axis. Our results suggest that the drastic change of multiferroic properties results from a switch of the spin-current magnetoelectric coupling in bulk TbMnO3 to symmetric magnetostriction in epitaxially-strained TbMnO3. These findings experimentally demonstrate that epitaxial strain can be used to control single-phase spin-driven multiferroic states.
Highlights
Our results show that highly strained high-quality TbMnO3 films grown coherently on (010) oriented YAlO3 substrates exhibit commensurate AFM with P||a as a ground state, while bulk shows an IC spin-spiral order with P||c17,18
The observed change of the ground state in TbMnO3 induced by two-dimensional growth-induced stress is by chance similar to the application of three-dimensional chemical pressure[30] or hydrostatic pressure[13,14]
The modified ground state can be attributed to a strain-tuned dominant magnetoelectric coupling mechanism, from antisymmetric magnetostriction[31,32,33] to symmetric magnetostriction[33,34,35]
Summary
A (100) YAlO3 substrate was used to prepare a relaxed reference sample expected to display bulk-like properties. Out-of-plane x-ray θ-2θ diffraction patterns (Fig. 1a) indicate the TbMnO3 films grown on both (010) and (100) YAlO3 to be single-phase without any twinning.
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