Direct real space observation of magneto-electronic inhomogeneity in ultra-thin film La0.5Sr0.5CoO3−δ on SrTiO3(001)

Abstract

Recent magnetotransport and neutron scattering measurements implicate interfacial magneto-electronic phase separation as the origin of the degradation in transport and magnetism in ultra-thin film La1−xSrxCoO3 on SrTiO3(001). Here, using low temperature scanning tunneling microscopy and spectroscopy the first direct, real space observation of this nanoscopic electronic inhomogeneity is provided. Films of thickness 12.4 nm (32 unit cells) are found to exhibit spatially uniform conductance, in stark contrast to 4.7 nm (12 unit cell) films that display rich variations in conductance, and thus local density of states. The electronic heterogeneity occurs across a hierarchy of length scales (5–50 nm), with complex correlations with both topography and applied magnetic fields. These results thus provide a direct observation of magneto-electronic inhomogeneity in SrTiO3(001)/La0.5Sr0.5CoO3 at thicknesses below 6–7 nm, in good agreement with less direct techniques.

Electronic and Structural Disorder of the Epitaxial La0.67Sr0.33MnO3 Surface

“…28 Using scanning tunneling spectroscopy (STS), we detected an EPS across the surface that is related to the nature of the staggered growth and chemical disorder. This relation between rough surface morphology and EPS has been reported for Cadoped LaCaMnO 3 films 34 and thus appears to be a common feature of the manganite perovskite family.…”

Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3−δ

“…The films (8 unit cells thick for all measurements presented here) were then naturally cooled in 600 Torr of O 2 . Such films have been subject to thorough prior structural and chemical characterization using high-resolution wide-angle X-ray diffraction, rocking curve analysis, grazing incidence in-plane diffraction, grazing incidence reflectivity, cross-sectional scanning transmission electron microscopy, electron energy loss spectroscopy, and scanning probe microscopy. − Briefly, the films are single-phase, (001)-oriented, atomically smooth epilayers with bulk-like electronic and magnetic properties in the thick film limit. Strain-induced oxygen vacancy ordering occurs in these layers, with the O-deficient planes parallel to the surface when grown on LaAlO 3 (001) …”

“…In order to address some of these pressing questions, we have applied electrolyte gating to ultrathin epitaxial films of La 0.5 Sr 0.5 CoO 3‑δ (LSCO), a ferromagnetic metallic oxide that we have previously characterized in detail in both bulk and thin film forms. − While this material is heavily hole-doped and is therefore expected to exhibit modest gate-induced changes even in EDLTs, the detailed knowledge of the x -dependent electronic properties in La 1– x Sr x CoO 3−δ (including in ultrathin films) provides an excellent platform for an improved understanding of the mechanisms of gating. Careful transport studies reveal that the application of negative gate bias leads to a reversible resistance decrease, at least to some threshold voltage, consistent with reversible hole accumulation, that is, predominantly electrostatic operation.…”

Soft x-ray absorption spectroscopy and magnetic circular dichroism as operando probes of complex oxide electrolyte gate transistors

“…As described previously 23 , epitaxial LSCO films were grown using high-pressure-oxygen reactive sputtering in 1.4 Torr of O2 from ceramic LSCO targets onto 10 × 10 mm 2 LaAlO3(001) substrates at 600 °C. Extensive structural, chemical, magnetic and transport characterization has been published [40][41][42][43] . To prepare EDLTs, 28-unit-cell-thick films were patterned into 3 × 3 mm 2 channels between two Pt side-gate electrodes 23,24 .…”