Orientation-dependent magnetism and orbital structure of strained YTiO3 films on LaAlO3 substrates

Abstract

The strain tuned magnetism of YTiO 3 film grown on the LaAlO 3 (110) substrate is studied by the method of the first principles, and compared with that of the (001)-oriented one. The obtained magnetism is totally different, which is ferromagnetic for the film on the (110) substrate but A-type antiferromagnetic on the (001) one. This orientation-dependent magnetism is attributed to the subtle orbital ordering of YTiO 3 film. The d xz /d yz -type orbital ordering is predominant for the (001) one, but for the (110) case, the d xy orbital is mostly occupied plus a few contribution from the d xz /d yz orbital. Moreover, the lattice mismatch is modest for the (110) case but more serious for the (001) one, which is also responsible for this contrasting magnetism.Recent advances in thin-film deposition techniques have made it possible to fabricate high quality epitaxial oxide thin films and heterostructures. Consequently, it becomes a very promising route to engineer physical properties of oxide thin films by strain. One of the strain effects is that the ground state phases and phase boundaries can be tuned away from the corresponding bulk constituents, which enables us to design "artificial" states with desired properties which are not available in bulk materials. [1][2][3][4] Generally, the strain is imposed by the constraint, namely coherently grown films share the same inplane lattice parameters with the underlying substrates. 5 Especially for the perovskites, due to the strain, the tilting and rotations of the oxygen octahedrons will change, which are crucial to determine the properties of perovskite oxides. 6,7 For example, LaTiO 3 films grown on compressive substrates (e.g. LaAlO 3 ) are predicted to show the A-type antiferromagnetism (A-AFM). In contrast, those grown on tensile substrates (e.g. LaScO 3 ) maintain the G-type antiferromagnetism (G-AFM) as in bulk. 8 It is reported that the compressive LaTiO 3 films may even undergo an insulator-to-metal transition. 9,10 Moreover, the strain effects depend on not only the simple lattice constants (e.g. compressive or tensile), but also the lattice orientations. It has been found that the electronic properties of films can be very different when growing along different orientations. Still taking the LaTiO 3 thin films as an example, the films grown on the (001)-oriented SrTiO 3 substrates show metallic behavior, while the films grown on the (110)-oriented DyScO 3 substrates are highly insulating, although the lattice mismatches are proximate for these two subtrates. 11YTiO 3 is another interesting correlated electronic system, which is a prototypical Mott-insulator with a ferromagnetic (FM) ground state. 12 Due to the small size of Y 3+ ion, YTiO 3 has a highly distorted orthorhombic structure. 13,14 From previous studies, it is known that the lattice distortions and orbital orderings are important a) Electronic mail: sdong@seu.edu.cn to understand the FM order in YTiO 3 . 12,13 Theoretical studies revealed that the FM order in bulk is stabilized by the distorted Ti...

Orientation-dependent ferroelectricity of strained PbTiO3 films

“…Even for a single material film, the growth orientation may alter the ground state. In a recent study, we found that the YTiO 3 film on LaAlO 3 becomes A-type antiferromagnetic when growing along the [001]-axis [12], while it retains ferromagnetism when growing along the [110]axis; this finding agrees with experimental observations [13,14]. For LaTiO 3 , the exchange coefficients and, thus, the Neel temperature were predicted to be significantly enhanced in the [111] bilayer compared with the [001] one [15].…”

Ultrafast optically induced ferromagnetic/anti-ferromagnetic phase transition in GdTiO3 from first principles

“…7,28 Previous theoretical work has also explored strain as a possible strategy for stabilizing the A-AFM phase in rare-earth titanates (and specifically GdTiO 3 ) although much larger values of strain were typically required. [29][30][31][32] Figure 6(a) now shows that excitation of the same IR-active phonon (now at 70.8 meV in the strained material) pushes GdTiO 3 across the phase boundary, stabilizing the A-AFM phase at lower peak electric fields than in the unstrained system. We find that the combined peak IR and Raman response stabilizes the A-AFM phase for E 0 > 2.5 MV/cm.…”

Magnetic order and electronic structure of [110]-oriented LaTiO3 films: A theoretical study

“…For example, LTO and YTO films grown on the compressive [001] LaAlO 3 (LAO) substrate were predicted to show A-type antiferromagnetism (AFM) although their bulks show different original magnetic orders [13,14]. In addition to the substrate constraint (e.g., compressive or tensile), the growth orientation is also important in determining the physical properties of oxide films and superlattices, such as orientation-dependent magnetism and orientationdependent metal-insulator transition [15][16][17][18][19][20].…”