Mapping a Magnetic Nanostructure

This Cs-corrected HAADF image shows an overview of several SiO2 spheres prepared for the investigation in STEM. Because of their high atomic number of the contained elements the magnetic layers appear much brighter in HAADF contrast than the Si.

The specimen consists of a SiO2 sphere coated with nm-thin layers of tantalum (Ta), ruthenium (Ru) and topmost a mixture of cobalt (Co), platinum (Pt), chromium (Cr) and oxygen (O). The top layer has a hedgehog-like structure, as becomes clear from the aberration corrected HAADF image. With EDS in a conventional STEM it was possible to localize the elements and to obtain a clearer picture of the layered structure. It is - for instance - quite easy to distinguish the seed layers consisting of Ru and Ta after quantifying the map using 8 x 8 binning to improve statistics of this quick measurement. The mixed element maps allow a number of conlusions, which are very important for the properties and the production process of the functional magnetic layers:

a) Co and Pt are distributed evenly in the top layer

b) Co and Pt form a closed film at the base of the single crystallites causing magneting connection and easy switching behaviour

c) Cr appears to be concentrated at the very surface of the structure.

Higher resolution mapping using EELS in a Cs-corrected STEM, published in APL (Magnetic hedgehog-like nanostructures, C. Brombacher, M. Falke, F. Springer, H. Rohrmann, A. Goncharov, T. Schrefl, A.Bleloch, M. Albrecht Appl. Phys. Lett. 97, (2010) 102508. DOI: 10.1063/1.3486679) shows that Cr oxide is isolating the outer parts of the single Pt-Co crystallites of this hedgehog-like structure from each other, so that the magnetic anisotropy can be used for device applications, like data storage.