  We calculate the spin relaxation time of mobile electrons due to spin
precession between random impurity scattering (D'yakonov-Perel' mechanism) in
electrically gated bilayer graphene analytically and numerically. Due to the
trigonal warping of the bandstructure, the spin relaxation time exhibits an
interesting non-monotonic behavior as a function of both the Fermi energy and
the interlayer bias potential. Our results are in good agreement with recent
four-probe measurements of the spin relaxation time in bilayer graphene and
indicate the possibility of an electrically-switched spin device.
