  We have investigated electronic and magnetic properties of graphene nanodisks
(nanosize triangular graphene) as well as electromechanical properties of
graphene nanojunctions. Nanodisks are nanomagnets made of graphene, which are
robust against perturbation such as impurities and lattice defects, where the
ferromagnetic order is assured by Lieb's theorem. We can generate a spin
current by spin filter, and manipulate it by a spin valve, a spin switch and
other spintronic devices made of graphene nanodisks. We have analyzed nanodisk
arrays, which have multi-degenerate perfect flat bands and are ferromagnet. By
connecting two triangular graphene corners, we propose a nanomechanical switch
and a rotator, which can detect a tiny angle rotation by measuring currents
between the two corners. By making use of the strain induced Peierls transition
of zigzag nanoribbons, we also propose a nanomechanical stretch sensor, in
which the conductance can be switch off by a nanometer scale stretching.
