Guerau Cabrera

Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures

Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present.

Electrostatic potential and valence modulation in La0.7Sr0.3MnO3 thin films

The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality.

Combined EELS and XAS Analysis of the Relationship between Depth Dependence and Valence in LSMO Thin Films

Lanthanum Strontium Manganite (LSMO) thin films are of interest due to their colossal magnetoresistive properties, which originates from double exchange related to the Mn 3+ to Mn 4+ charge states [1]. The local magnetic properties of the film are also directly related to the lattice strain at the film/substrate interface, and are tied to the strong lattice-electron interaction related to the MnO6 octahedra in the perovskite structure. The distortion of these octahedra is related to both mechanical strain caused by film/substrate misfit and the radial difference between La and Sr [2]. While x-ray characterization methods have illuminated oxidation states in these systems, [3] prior x-ray studies lack the spatial resolution of TEM. While the 3 to 4 trend as a function of LSMO thin film thickness is well established [1], the relationship between depth dependence and charge state along with accompanying structural effects is not well documented.