Magnetic orders of LaTiO3 under epitaxial strain: A first-principles study

Abstract

Perovskite LaTiO 3 bulk is a typical Mott-insulator with G-type antiferromagnetic order. In this work, the biaxial strain effects on the ground magnetic order of LaTiO 3 films grown on various substrates have been studied. For the compressive strain, LaTiO 3 films grown on LaAlO 3 , LaGaO 3 , and SrTiO 3 substrates undergo a phase transition from the original G-type antiferromagnet to A-type antiferromagnet. The underlying physical mechanisms are the lattice distortions tunned by strain. While for the tensile strain, the BaTiO 3 and LaScO 3 substrates have been tested, which show a tendency to transit the LaTiO 3 to the C-type antiferromagnet. Furthermore, our calculations find that the magnetic transitions under epitaxial strain do not change the insulating fact of LaTiO 3 .Perovskite oxides ABO 3 have attracted continuing attention and been intensively investigated due to their novel physical properties and a broad range of technical applications. 1 Among abundant perovskite compounds, the canonical Mott insulator RTiO 3 (R 3+ denotes a rareearth ions) are physically interesting due to the complex couplings between the orbital, spin, lattice degrees of freedom of Ti's 3d electron which is localized by the strong Coulombic interaction. In RTiO 3 perovskites, the ligand crystal field from the oxygen octahedron splits the 5-fold 3d levels into two groups: the 3-fold t 2g orbitals and the 2-fold e g orbitals. The Fermi level is located in the t 2g levels, and the t 2g orbitals are highly localized due to the p-d hybridization. Moreover, the GdFeO 3 -type structure distortions, which combine the tilts and rotations of the oxygen octahedrons, are prominent in the orthorhombic RTiO 3 . According to previous studies, 2-4 the ground magnetic phase of RTiO 3 transits from the ferromagnetism to G-type antiferromagnetism, with increasing size of R or in other words with weaking GdFeO 3 -type distortions, 5 as shown in Fig. 1(a).In the RTiO 3 bulks, compounds with small GdFeO 3 -type distortions exhibit the G-type antiferromagnetic (AFM) ordering, e.g. LaTiO 3 , and the large ones tend to lead the FM ordering, e.g. YTiO 3 . In addition, it is well known that perovskite oxides may be sensitive to external factors. 6-8 For example, recently the use of epitaxial strain has attracted great attentions due to many unexpected effects on thin films, 8-12 which has been proved to be a useful route to design potential devices.In this work, the effects of epitaxial strain on the ground magnetic order of LaTiO 3 films will be studied using the first-principles calculations, as illustrated in Fig. 1(b). Our calculations predict that a robust Atype AFM phase can be stabilized by the compressive strain. In contrast, LaTiO 3 films remain G-type AFM under moderate tensile strain, but have a tendency to become the C-type AFM with further increasing the tensile strain. LaTiO 3 has the orthorhombic structure (space group Pbnm) 9,13 with the experimental lattice constants of a=5.636Å, b=5.618Å, and c=7.916Å, containing 4 formula units. 14 In t...

(LaTiO3)n/(LaVO3)n as a model system for unconventional charge transfer and polar metallicity

“…A 7 × 7 × 5, 5 × 7 × 7 and 7 × 7 × 5 Monkhorst-Pack k-point mesh centered at Γ point are adopted for ( The Hubbard repulsion U eff (= U − J) is imposed on Ti's/V's 3d and La's 4f orbitals using the Dudarev implementation [26]. According to previous literature [27][28][29], U eff (Ti)=2.3 eV, U eff (V)=3 eV, and U eff (La)=8 eV are proper to reproduce the experimental properties and thus are adopted as default parameters in the following calculations, if not noted explicitly.…”

Magnetism and electronic structure of (001)- and (111)-oriented LaTiO3 bilayers sandwiched in LaScO3 barriers

“…The optimized equilibrium values for lattice con- Table I, the G-AFM have the lowest energy and the C-AFM is the first excited state with a proximate energy due to the strain effect, similar to the pure LTO film grown on the LSO substrate. 31 The energy difference ∆E and the local magnetic moment M Ti do not change too much when n changes from 2 to 4 for these (001)-oriented SLs. Such a behavior is due to the highly insulating LSO barrier, namely these ultra-thin LSO layers are enough to isolate LTO bilayers.…”

“…Our previous DFT calculation reported that the LTO film has a tendency to approach the C-AFM under tensile strain from substrates with relative large lattice constants, such as LSO used in the present work. 31 For these SLs, both the lattice constants along the c-axis and inner atomic positions are fully optimized until the Hellman-Feynman forces are less than 10 meV/Å.…”

“…Last but not the least, the tensile strain from LSO will tune the crystal structure of LTO. 31 Our density-functional theory (DFT) calculations were performed using the projector-augmented wave (PAW) potentials, as implemented in the Vienna ab initio Simulation Package (VASP). 32,33 The electronic correlation is treated using the local density approximation (LDA) with Hubbard U .…”

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

“…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.…”