Induced Ferromagnetism in Cobalt/Graphene Heterostructure by Proximity Effect
Yao-Jui Chan1,3*, Chih-Heng Huang1, Yin-Ming Chang1, Yi-Ying Lu1, Shih-Yu Wu1, Der-Hsin Wei2, Chien-Cheng Kuo1
1Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
2National Synchrotron Radiation Center, Hsinchu, Taiwan
3Insitute of Physics, Academia Sinica, Taipei, Taiwan
* Presenter:Yao-Jui Chan,
The interface magnetism is of interest to the fundamental research and application on the spintronics based on two dimensional (2D) materials because it provides a new route to introduce and manipulate ferromagnetism in heterostructures. In 2D materials, graphene is one of the ideal platforms for spintronics due to it can play as a promising channel material for spin transportation with high mobility as well as long spin diffusion length. Although many existing results have measured magnetoresistance in the FM/graphene heterostructure, the interface magnetism seems to remain mysteries. Probing the interface magnetism is a long-standing challenge in the heterostructure since the magnetic response only reflects global magnetic properties in the measurement conducted by the conventional measurement tools. In this talk, we investigate the interface magnetism of cobalt/graphene heterostructures by using an element and spin specific measurements using X-ray absorption spectroscopy (XAS) with magnetic circular dichroism (XMCD). An induced ferromagnetic phase in graphene, evidenced by distinct dichroism at π* state in C K-edge spectra, is only observed in the case while graphene capped by the thick Co films. This ferromagnetic phase occurs in coincident with the transition of Co layers from superparamagnetic to ferromagnetic phase. These observations suggest that the ferromagnetic order in the graphene layer is activated through the proximity effect at the interface, mediated with the π* band in graphene and 3d band in cobalt. Furthermore, this proximitized ferromagnetic phase in graphene arises from the magnetic dipolar interaction, rather than the intrinsic exchange interaction, of Co also suggests that the dipolar interaction dominates the magnetic behaviors in both graphene and the capped Co film. Our results further shed light on an efficient way to integrate the ferromagnetic nanoparticles with graphene on the application of graphene-based spintronics through manipulating the interface magnetism.

Keywords: interface magnetism, proximity effect , graphene, nanoparticle