Photoemission electron microscopy of three-dimensional magnetization configurations in core-shell nanostructures

Abstract

We present a photoemission electron microscopy method that combines magnetic imaging of the surface and of the inner magnetization in three-dimensional core-shell nanostructures. The structure investigated consists of a cylindrical nickel core that is completely surrounded by a shell of iron oxide and silicon oxide layers. The method enables one to image the magnetization configuration of the nickel core even though the shell is thicker than the mean-free path of the photoelectrons. Characteristic L 3 and L 2 edges can be observed not only in the yield of the photoelectrons emitted from the surface of the nanostructure but also in its shadow. X-ray magnetic circular dichroism in the electron yield of the x rays absorbed and transmitted by the multilayered nanowire allows for the individual imaging of the magnetization configurations of the iron oxide tube and the nickel core. The method suggests novel approaches for the characterization of the magnetic and material properties of complex three-dimensional nanostructures.

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.…”

“…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). This has been named shadow XMCD-PEEM [26]. This provides a technique with an interesting hybrid sensitivity, within the set of microscopy techniques mentioned above.…”

“…These domain walls have been predicted to be liable to reach high and robust velocities [21], due to their specific topology providing them with a protection against transformations [25]. While domains in tubes [26,27] and conventional transverse walls in wires [28] had been imaged, recently some of us provided the experimental proof of the existence of…”

“…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).…”

“…These domain walls have been predicted to be liable to reach high and robust velocities [21], due to their specific topology providing them with a protection against transformations [25]. While domains in tubes [26,27] Let us review again the above-mentioned microscopy techniques, in the light of 3D imaging. SPLEEM and SEMPA typically probe the topmost atomic layer of matter.…”