Fully Magnetically Polarized Ultrathin La _0.8Sr _0.2MnO ₃ Films

Abstract

We report the observation of fully magnetically polarized ultrathin La _0.8Sr _0.2MnO ₃ films by using LaMnO ₃ and La _0.45Sr _0.55MnO ₃ buffer layers grown epitaxially on SrTiO ₃(001) substrates by molecular beam epitaxy. Specifically, we show that La _0.8Sr _0.2MnO ₃ films grown on 12-unit-cell LaMnO ₃ have bulk-like magnetic moments starting from a single unit cell thickness, while for the 15-unit-cell La _0.45Sr _0.55MnO ₃ buffer layer, the La _0.8Sr _0.2MnO ₃ transitions from an antiferromagnetic state to a fully spin-polarized ferromagnetic state at 4 unit cells. The magnetic results are confirmed by X-ray magnetic circular dichroism, while linear dichroic measurements carried out for the La _0.8Sr _0.2MnO ₃/La _0.45Sr _0.55MnO ₃ series show the presence of an orbital reorganization at the transition from the antiferromagnetic to ferromagnetic state corresponding to a change from a preferred in-plane orbital hole occupancy, characteristic of the A-type antiferromagnetic state of La _0.45Sr _0.55MnO ₃, to preferentially out of plane. We interpret our findings in terms of the different electronic charge transfers between the adjacent layers, confined to the unit cell in the case of insulating LaMnO ₃ and extended to a few unit cells in the case of conducting La _0.45Sr _0.55MnO ₃. Our work demonstrates an approach to growing ultrathin mixed-valence manganite films that are fully magnetically polarized from the single unit cell, paving the way to fully exploring the unique electronic properties of this class of strongly correlated oxide materials.