Growth of ultra-thin Cobalt on fullerene (C60) thin-film: in-situ investigation under UHV conditions

Abstract

With the advent of organic spintronics, material such as fullerene (C60) is drawing immense attention due to the long spin relaxation time. C60 based spin valve structures are always challenging due to the complicated structure at the interfaces of metal (cathode) and C60. In the present work, the growth of e-beam evaporated Co films on the C60 layer has been studied in-situ, starting from a fraction of nanometer to tens of nanometers, using reflection high energy electron diffraction (RHEED), electron transport (ET) and magneto-optic Kerr effect (MOKE) measurements. While RHEED and ET provided information about structure and film morphology, in-situ MOKE provided information about magnetic properties, thus making it possible to correlate the evolution of magnetic properties with that of structure and morphology of the Co thin film. The film grows via island growth, where small isolated islands grow larger to connect with other islands and eventually combine into a continuous film at around 75 Å thickness. Combined analysis of Kerr intensity and resistivity variation with Co thickness revealed the origin of the 23 Å thick magnetic dead layer at the interface, which is attributed to the formation of small clusters with paramagnetic or superparamagnetic properties.