High‐T_C Interfacial Ferromagnetism in SrMnO₃/LaMnO₃ Superlattices

Abstract

Heterostructures of strongly correlated oxides demonstrate various intriguingand potentially useful interfacial phenomena. LaMnO 3 /SrMnO 3 superlattices are presented showcasing a new high-temperature ferromagnetic phase with Curie temperature, T C ≈360 K, caused by electron transfer from the surface of the LaMnO 3 donor layer into the neighboring SrMnO 3 acceptor layer. As a result, the SrMnO 3 (top)/LaMnO 3 (bottom) interface shows an enhancement of the magnetization as depth-profiled by polarized neutron reflectometry. The length scale of charge transfer, λ TF ≈2 unit cells, is obtained from in situ growth monitoring by optical ellipsometry, supported by optical simulations, and further confirmed by high resolution electron microscopy and spectroscopy. A model of the inhomogeneous distribution of electron density in LaMnO 3 /SrMnO 3 layers along the growth direction is concluded to account for a complex interplay between ferromagnetic and antiferromagnetic layers in superlattices.

Polaronic Emergent Phases in Manganite-based Heterostructures

“…One can see a different behavior during the growth of LMO and SMO layers. Namely, ∆(t) increases linearly by the LMO growth in agreement with an increase in the LMO thickness similar to the case of LSMO growth [34] (see also Figure 2). In contrast, the SMO layer displays a complex behavior clearly seen in the inset in Figure 11-the initial fast increase in ∆(t), followed by slowing it down at the end of SMO growth.…”

“…By applying SERS, we observed such phases at the surface of a manganite [32] because of the symmetry-break-induced electronic reconstruction, theoretically predicted by Calderon et al [33]. The importance and novelty of artificial nanoscale EPs is highlighted by the observations of (1) a high-T C ferromagnetic EP at the SrMnO 3 (top)/LaMnO 3 (bottom) (SMO/LMO) interface [34] caused by the electron transfer from the LMO "donor" layer into the SMO "acceptor" layer, and (2) the electric-field-induced resistance switching in the layer-by-layer fashion [35] of electrically highly isolated "dead layer" at the La 0.7 Sr 0.3 MnO 3 (LSMO) surface and formation of the embedded conducting layers, which allow a robust multi-state memristive functionality.…”

“…Thus, the ellipsometric phase shift rate, dΔ/dD, is assumed to be a probe of the charge density/u.c. or, in case of (LMO)m/(SMO)n superlattices 34 of the averaged doping level, x = n/(m + n) in superlattices (SLs) (see Section 3.3 below). The scheme of the metalorganic aerosol deposition (MAD) apparatus equipped with a precision liquid pump system and in situ growth monitoring by means of optical ellipsometry.…”

“…Thus, the ellipsometric phase shift rate, d∆/dD, is assumed to be a probe of the charge density/u.c. or, in case of (LMO) m /(SMO) n superlattices 34 of the averaged doping level, x = n/(m + n) in superlattices (SLs) (see Section 3.3 below). The currently developed MAD was shown to be successful in preparation of various oxide films and heterostructures of correlated oxides with very high crystalline quality.…”

“…Perovskite heterostructures provide a rich playing field for design and engineering of oxide interfaces with the final goal to obtain interfacial EPs with unusual electronic behavior not present in the parent layers [105]. Recently we have reported [34] the MAD grown LaMnO 3 /SrMnO 3 (LMO/SMO) superlattices (SLs), showing a ferromagnetic EP with Curie temperature T C ≈ 360 K, originated from the electron transfer from the LMO "donor" layer to the overlying "acceptor" SMO layer. As a result, the SMO(top)/LMO(bottom) interface acquires ferromagnetic magnetization revealed by polarized neutron reflectometry.…”