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UBC Theses and Dissertations

The excess of dephasing rate in the gas annealed CVD graphene Shin, Hyungki


Graphene was expected to prove useful in the field of spintronics because a long spin relaxation time (few micro second) was theoretically expected. However, experimental results using exfoliated graphene have shown that the spin relaxation time is a few orders of magnitude less than the theoretical prediction. It was discovered that the reason for this unexpected shorter spin relaxation time is the presence of magnetic moments on graphene and magnetic moments exist on most forms of graphene. Many theoretical articles expected these magnetic moments to arise due to graphene defects. However, it is not experimentally clear where and how they arise. To answer where and how, we investigates it with dephasing rate (phase relaxation rate) monitored via weak localization on graphene, grown by chemical vapour deposition (CVD graphene). The experiments are performed on field-effect devices made from CVD graphene on various substrates under perpendicularly applied magnetic fields at 4.2 K. The samples are thermally annealed under various conditions, which is a commonplace technique used to clean the surface of graphene. Only the gas annealing induces the additional source of dephasing rate on CVD graphene. However, this could not be seen in before-annealed samples and vacuum annealed samples. Additional experiment confirms that this additional source on gas annealed sample has the magnetic property. The result on this thesis can help answer the origin of magnetic moments on graphene.

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