Nanoscale domain evolution in thin films of multiferroicTbMnO3

Abstract

Control of the domain structures in multiferroic thin films is of crucial importance in order to gain access to their functional responses. Here we report on the evolution of the nanodomain structures observed in epitaxial thin films of multiferroic TbMnO 3 grown on SrTiO 3 substrates. Thin films with thickness ranging from 2 to 140 nm were grown at 0.25 and 0.9 mbar oxygen partial pressures. Transmission electron microscopy was employed to study and understand the domain evolution. A transition from a fully coherent, highly strained, tetragonal film to a partially coherent, distorted, orthorhombic structure occurs via a transformation twinning mechanism, giving rise to four different domain orientations. Then, at larger thicknesses, a transition to the fully relaxed orthorhombic structure occurs via changes in the domain-substrate orientation relationships leading to only two domain variants. Differences have been observed in the strain relaxation behavior for films grown at different oxygen pressures. All the observations have allowed us to understand the evolution of the domain structures and to accurately explain the measured orthorhombic distortion. This mechanism can be generalized for ͓001͔-oriented orthorhombic perovskites grown on cubic substrates with large misfit values.

Interface-dependent rectifying TbMnO3-based heterojunctions

“…It appears to be consistent with the existence of multiple domain variants in the lattice-distorted TMO films as a result of the coherent relationship with the cubic NSTO substrate. 39,41 This is also supported by the bright-field TEM images, where the Moire fringes (marked with dashed circle in Fig.7(a) and 7(b)) are generated due to the overlap between two kinds of grains with a small misalignment. In some local areas of observation, a tilt angle of ∼6.5 • between the (110) TMO and the (100) NSTO directions was directly observed in the film grown at 700 • C (Fig.…”

“…Thus, in the TMO films, the arrangements of the multiple domain variants as reported previously give rise to complex microstructures, and the shear displacements lead to a lattice symmetry lower than orthorhombic. 39,41 It is well know that thin films of complex oxides grown on single crystal substrates are often distorted with a lower symmetry than the bulk lattice structure. 59,60 Misfit dislocations, disordered domains and strain are the common complexities which exist at oxide interfaces and often dictate the transport properties of the junctions.…”

“…After deposition the samples were cooled down to the room temperature in 1 atm oxygen atmosphere with a rate of 3 • C/min. It should be noted that the temperature range we used during the PLD growth is similar to what other group used in literature, e.g., Daumont et al grew their TbMnO 3 films on SrTiO 3 at 750 • C. [39][40][41] To study the structure of the as-grown TMO films, x-ray diffraction (XRD) data were recorded (SmartLab, Rigaku). Figure 1(a) show the θ -2θ scans of two samples grown at 780 • C and 700 • C. Both TMO films are single phase and c-axis oriented, consistent with the previous results, 39,40 but the XRD peaks of the 780 • C grown sample are slightly stronger than those of the 700 • C sample, indicating a better crystallinity.…”

“…But as suggested in previous studies, the TMO thin films are orthorhombically distorted and likely break into ferroelastic nanodomains, which is responsible for the absence of ferroelectrisity. 39,41 …”

Interfacial magnetic coupling in ultrathin all-manganite La0.7Sr0.3MnO3-TbMnO3 superlattices

“…is higher than that of [4/8] 16 SL (2.25 l B /u.c.). Furthermore, nanoscale domains were observed in TMO thin films, 44 and their interactions with the magnetic domains in LSMO will be investigated in the future. 45,46 In summary, the emergence of significantly enhanced coercivity and exchange bias in all-manganite LSMO-TMO SLs underscores such unit-cell-controlled heterostructures as a viable route towards tailored artificial magnetic materials.…”