Interfacial Coupling-Induced Ferromagnetic Insulator Phase in Manganite Film

Abstract

Interfaces with subtle differences in atomic and electronic structures in perovskite ABO3 heterostructures often yield intriguingly different properties, yet their exact roles remain elusive. Here, we report an integrated study of unusual transport, magnetic, and structural properties of Pr0.67Sr0.33MnO3 film on SrTiO3 substrate. The variations in the out-of-plane lattice constant and BO6 octahedral rotation across the Pr0.67Sr0.33MnO3/SrTiO3 interface strongly depend on the thickness of the Pr0.67Sr0.33MnO3 film. In the 12 nm film, a new interface-sensitive ferromagnetic polaronic insulator (FI') phase is formed during the cubic-to-tetragonal phase transition of SrTiO3, apparently due to the enhanced electron-phonon interaction and atomic disorder in the film. The transport properties of the FI' phase in the 30 nm film are masked because of the reduced interfacial coupling and smaller interface-to-volume ratio. This work demonstrates how thickness-dependent interfacial coupling leads to the formation of a theoretically predicted ferromagnetic-polaronic insulator, as illustrated in a new phase diagram, that is otherwise ferromagnetic metal (FM) in bulk form.

Anomalously deep polarization in SrTiO3 (001) interfaced with an epitaxial ultrathin manganite film

“…A metallic surface state exists on STO (001) [11] and may be related to the presence of oxygen vacancies [12]. These observations suggest that the interface is more complex than anticipated, including possible charge transfer [6], lattice relaxation [7], stoichiometric variation [13,14], defect effect [15][16][17][18], and thickness-dependent interfacial coupling [19].…”

Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

“…Adding strong electron−lattice coupling and easily formed oxygen vacancies to this mix, the result is a large number of coupled degrees of freedom. Therefore, it is not surprising that TMO heterostructures exhibit highly unusual behavior, induced by interfaces between different oxides where symmetry discontinuities occur, leading to properties that are absent in bulk (1)(2)(3)(4)(5). A wellknown example is the LaAlO 3 /SrTiO 3 (001) heterostructure, where a 2D electron gas with high mobility forms at the interface between two insulating oxides (6), including the appearance of superconductivity (7) and background ferromagnetic (FM) ordering (8).…”

“…In many cases, the symmetry discontinuity at the interface strongly modifies the transition metal−oxygen octahedra network, inducing changes in local structure (bond geometry) and local stoichiometry. These changes have been shown to result in exotic magnetic properties such as antiferromagnets (AFM) built from FM layers (9), interface-driven magnetic phases absent in bulk (5), antiparallel spin alignment at manganite−ruthenate interfaces (10), and fine control over magnetic anisotropy by interfacing manganites and iridates (11). Advances in epitaxial synthesis provide a fine control over interfaces that is necessary to realize novel magnetic systems hitherto unseen in TMOs, such as spontaneous magnetic reversal (SMR) and exchange spring (12)(13)(14).…”

The Atomic Circus: Small Electron Beams Spotlight Advanced Materials Down to the Atomic Scale

“…In perovskite ABO 3 heterostructures, for example, an interface with subtle differences in atomic and electronic structures often yields intriguingly different properties. Chow's group has reported an integrated study of the unusual transport, magnetic, and structural properties of Pr 1− x Sr x MnO 3 (PSMO) on a SrTiO 3 (STO) substrate . Atomically resolved STEM annular bright‐field (ABF) images show asymmetric and distorted octahedral rotations in the Pr 0.67 Sr 0.33 MnO 3 film, which is considerably different from the intrinsic symmetric ones, as seen in Figure e–m.…”