Photoemission electron microscopy study of sub-200 nm self-assembled La0.7Sr0.3MnO3 epitaxial islands

Abstract

The chemical composition and the magnetic structure of individual La0.7Sr0.3MnO3 (LSMO) ferromagnetic manganite epitaxial nanostructures less than 200 nm in width are explored using Photoemission Electron Microscopy (PEEM). X-ray absorption spectra (XAS) provide separate information on the surface and the bulk composition of the nanoislands and give evidence of Mn(2+) present on the surface of otherwise stoichiometric nanostructures. Ferromagnetic domains less than 70 nm are resolved using X-ray magnetic circular dichroism (XMCD), which allows for the detection of magnetic vortex states in both (001)LSMO square and (111)LSMO triangular manganite nanoislands. The evolution of single nanostructures under an in-plane magnetic field is seen to depend on the specific nanoisland size and geometry. In particular, PEEM XMCD imaging allows detecting opposite chiralities as well as a variety of magnetization behaviors for different nanoislands.

Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

“…Several effects mentioned need however to be considered to extract true spatial and contrast information such as plane of focus, extraction voltage, electric field distortion and electron background level. While we illustrated the method with experiments we performed on cylindrical nanowires, it can be applied to any object of size 10−200 nm imaged by shadow XMCD-PEEM, such as those already reported [26,[34][35][36], provided that material parameters such as exchange stiffness and magnetization are known, to perform reliable micromagnetic simulations. In particular, sufficient geometrical information about the sample remains required, as its projected shadow does not characterize fully its shape.…”

“…Thus it is not strictly surface sensitive, however not suitable a priori to probe magnetic systems in depth. However, as mentioned above XMCD-PEEM was recently applied to three-dimensional objects lying on a supporting surface [26,29,[34][35][36]. As the X-ray beam is tilted with respect to the normal to the supporting surface, this provides magnetic sensitivity both at the surface of the object, and gives rise to a shadow on the supporting surface, whose inspection yields information about magnetization in the core (Figure 1a,b).…”

Interfaces and Nanostructures of Functional Oxide Octahedral Framework Structures

“…In octahedral framework systems, the flexibility of the lattice to accommodate large interfacial dissimilarities favors the wetting of the substrate hindering the formation of islands. However, interesting results have been obtained by the combination of different structural families using chemical solution deposition, like, for instance, perovskite/rock-salt (La 0.7 Sr 0.3 MnO 3 /MgO) (Abellán et al, 2012), fluorite/perovskite (CeO 2 /LaAlO 3 ) (Gibert et al, 2010), and perovskite/fluorite (La 0.7 Sr 0.3 MnO 3 /YSZ) (Zabaleta et al, 2013). In all cases, interfaces appear highly dislocated and therefore affected by strain fields that may extend over a few unit cells into the island with negative effects on their functionalities, such as the induction of polarization instabilities in ferroelectric materials (Chu et al, 2004).…”

Magnetic vortex evolution in self-assembled La0.7Sr0.3MnO3 nanoislands under in-plane magnetic field

“…26 X-ray absorption spectra (XAS) showed bulk like composition and Mn 2+ rich surfaces, which may account for the loss in magnetization measured by SQUID magnetometry. 27 Figures 1(a) and 1(b) show the topography and the corresponding magnetic signal image, respectively, of the self-assembled LSMO nanoislands in remanence. The MFM image was taken after saturating the sample ex situ with a 400 kA/m field applied perpendicular to the sample substrate, and in the direction opposite to the tip stray field.…”

“…In our recent work, 26,27 we have described the rich variety of magnetic structures adopted by solution-derived self-assembled LSMO nanoislands, a system with intrinsic biaxial magnetocrystalline anisotropy in contrast to the more common permalloy nanodots. In particular, we showed that the vortex state is the preferred configuration for a broad range of LSMO nano-sized geometries.…”