Interfaces and dimensionality effects play an important role in the magnetic and transport properties of spintronic devices [1]. They are generally multilayers with two thin ferromagnetic films (cobalt or/and manganite) separated by a third material (insulator or (in-)organic semiconductor).

In this work we study by means of zero-field ⁵⁹Co NMR and Squid magnetometry the correlation between microstructure  and magnetic properties of thin (5-15 nm) Co layers deposited on top of organic semiconductor 50-nm thick Alq3.  ⁵⁹Co NMR is sensitive enough to obtain detailed information on interfaces (e.g topology) and individual layers with the thickness of a few monolayers embedded in the multilayer structure. The local field at the ⁵⁹Co nucleus easily distinguishes different local environment, transforming NMR into a sensitive local structural probe. The crystalline phase (i.e fcc, hcp or bcc Co), the presence of impurities and the type of interface can also be identified in the cobalt spectra Uuing NMR. Effects of an insulating barrier Alox with thickness varying from 0 to 5 nm in Co/(Alox)/Alq3/Si multilayers are investigated too. These results are compared to the morphological properties of the same heterostructures investigated by means of  atomic force microscopy and to the magnetic properties measured by Squid magnetometry. The measured RT hysteresis loops show reproducible and comparable coercive field of the oredr of 15 Oe with no strong dependence of the barrier thickness. Combining  magnetic and morphological data it was found that 2 nm thick barrier can assure a good quality of the Co layer.

[1] Dediu et al. Phys. rev. B 78 115203 (2008)

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