Abstract
Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden–Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1–xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature Tg ≈ 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.
Highlights
Vacuum deposition of epitaxial thin films with in situ monitoring by reflection high energy electron diffraction (RHEED) is a technique capable of controlling growth of complex oxides at the unit-cell level.[1,2] By sequentially depositing an integer number of unit cells of different materials, layered structures can be formed
Layer-by-layer growth occurs within a certain window of adatom surface mobility, which is strongly influenced by substrate temperature.[40]
In the case of LSMO, RHEED oscillations were observed over a wide range of conditions, and stoichiometric cation transfer from target to film was confirmed by growth of 400 nm thick LSMO films followed by energy dispersive X-ray (EDX) analysis
Summary
Vacuum deposition of epitaxial thin films with in situ monitoring by reflection high energy electron diffraction (RHEED) is a technique capable of controlling growth of complex oxides at the unit-cell level.[1,2] By sequentially depositing an integer number of unit cells of different materials, layered structures can be formed. While structures with n > 2 are rarely able to be produced through conventional ceramic synthesis, examples with n ≤ 6 have been grown epitaxially, and in addition the incorporation of different perovskite blocks within the RP structure is possible.[3,5,11−13] A set of compounds that has attracted great attention is the (SrO)(La(1−x)SrxMnO3)n series, where the mixed valence manganite perovskites La(1−x)SrxMnO3, which are well-studied compounds with a rich magnetic phase diagram, can be further modified by the introduction of nonmagnetic SrO layers This is of particular interest for x = 0.33 La0.67Sr0.33MnO3 (LSMO), which is the archetypal colossal magnetoresistive oxide.
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