Origin of insulating weak-ferromagnetic phase in ultra-thin La0.67Sr0.33MnO3 films on SrTiO3 substrate

Abstract

We investigate the origin of insulating weak-ferromagnetic phase in ultra-thin epitaxial La0.67Sr0.33MnO3 (LSMO) films on SrTiO3 substrate using density functional theory calculation together with X-ray linear dichroism (XLD). The calculations show that symmetry breaking of the crystal field at the LSMO surface largely lowers the energy level of Mn d3z2 orbital at the surface and leads to full occupancy of the d3z2 orbital in majority spin channel, and XLD spectra clearly show the preferential occupation of Mn d3z2 orbital at the surface. Such an orbital reconstruction and charge redistribution in the ultra-thin films largely suppresses double-exchange interaction and favors super-exchange interaction, resulting in G-type antiferromagnetic spin ordering and insulating state. The anisotropic exchange interaction due to spin-orbital interaction leads to spin canting, and thus the films show weak ferromagnetism.

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“…S3 of supplementary data), whereas, TL2 (001) sample displays the metallic behaviour with metal-insulator transition (T MI ) around T ∼ 200 K. On the other hand, all other samples show completely metallic behaviour for different (LSMO and SRO) thicknesses. Such higher order of magnitude in the electrical resistivity was reported in the literature with decreasing thickness of the film in monolayers and heterostructures of LSMO and SRO [65][66][67] . The metallic behaviour increases progressively with increasing the externally applied magnetic field.…”

Effect of strain on magnetic and orbital ordering of LaSrCrO3/LaSrMnO3 heterostructures

“…The line shapes are consistent with previous measurements and theoretical calculations for strained LSMO films. 39,40,53,54 The orbital polarization is quantified by plotting the area of the shaded regions in Figure 5(b) as a function of the c/a ratio in Figure 5(c). The change in the integrated L 2 XLD sign from negative for the tensile strained sample on STO to positive for the compressively strained sample on LSAT and LAO is consistent with the predicted change in orbital occupation due the strain-induced Jahn-Teller-like distortion.…”