Ab initioelectronic and magnetic structure in La_0.66Sr_0.33MnO₃: strain and correlation effects

Abstract

Abstract. The effects of tetragonal strain on electronic and magnetic properties of strontium-doped lanthanum manganite, La 2/3 Sr 1/3 MnO 3 (LSMO), are investigated by means of density-functional methods. As far as the structural properties are concerned, the comparison between theory and experiments for LSMO strained on the most commonly used substrates, shows an overall good agreement: the slight overestimate (at most of 1-1.5 %) for the equilibrium out-of-plane lattice constants points to possible defects in real samples. The inclusion of a Hubbard-like contribution on the Mn d states, according to the so-called "LSDA+U" approach, is rather ineffective from the structural point of view, but much more important from the electronic and magnetic point of view. In particular, full half-metallicity, which is missed within a bare densityfunctional approach, is recovered within LSDA+U, in agreement with experiments. Moreover, the half-metallic behavior, particularly relevant for spin-injection purposes, is independent on the chosen substrate and is achieved for all the considered in-plane lattice constants. More generally, strain effects are not seen to crucially affect the electronic structure: within the considered tetragonalization range, the minority gap is only slightly (i.e. by about 0.1-0.2 eV) affected by a tensile or compressive strain. Nevertheless, we show that the growth on a smaller in-plane lattice constant can stabilize the out-of-plane vs in-plane e g orbital and significatively change their relative occupancy. Since e g orbitals are key quantities for the double-exchange mechanism, strain effects are confirmed to be crucial for the resulting magnetic coupling.

A key role of tensile strain and surface termination in formation and properties of La0.7Sr0.3MnO3 composites with carbon nanotubes

“…First, the unit cell of bulk LSMO was optimized, and the a translation vector is found to be equal to 3.886 Å which is in a good agreement with experimental data (a=3.876 Å [30] and a=3.87 Å [31]) and previous theoretical calculations (a=3.89 Å) [27]. Then, LSMO(001) surface was constructed by cutting it along the 4 corresponding crystallographic plane.…”

“…D3 Grimme correction of weak dispersion interactions [26] was used in order to describe the interaction between nanotubes and LSMO substrate correctly. The U=2 and J=0.7 eV parameters for Mn atoms were adopted from earlier calculations of LSMO and carefully tested with respect to the lattice parameters and electronic properties of both bulk and slab LSMO [27][28][29]. Full geometry optimization was performed until the forces acting on atoms were less than 0.01 eV/Å.…”

Electronic and magnetic structure of the(LaMnO3)2n/(SrMnONanda1, Satpathy2 2009Phys. Rev. B655621View full textAdd to dashboardCite

“…2 shows, the most important feature in the electronic structure of ͑LMO͒ 2 / ͑SMO͒ 1 is that the delocalized e g states of both Mn-0 ͑Mn atoms at the interface͒ and Mn-1 ͑Mn atoms inside the LMO part͒ are partially occupied, which is in agreement with the earlier electronic structure calculations. 17 These partially occupied e g states will mediate a strong Zener ferromagnetic double exchange [18][19][20] between the Mn-t 2g core spins, which wins over the antiferromagnetic superexchange, so that a uniform ferromagnetic ordering throughout the superlattice is stabilized. The calculation of the Mn-Mn exchange interactions discussed below indicates that the FM ordering is stable, quite similar to the equivalent alloy compound La 2/3 Sr 1/3 MnO 3 .…”

Conditions for the growth of smooth La0.7Sr0.3MnO3 thin films by pulsed electron ablation

“…Impressive efforts have been made in order to understand the complex physics characteristic for these materials, implicating massive experimental and theoretical investigations [2,3]. In addition the interest towards device applications stimulated detailed surface studies including a wide spectrum of various spectroscopy [4] and microscopy techniques [5], supported often by thorough ab initio simulations [6,7].…”