  Tunnelling of electrons in graphene-based junctions is studied theoretically.
Graphene is assumed to be deposited either directly on a ferromagnetic
insulator or on a few atomic layers of boron nitride which separate graphene
from a metallic ferromagnetic substrate. Such junctions can be formed by
appropriate external gating of the corresponding system. To describe low-energy
electronic states near the Dirac points, certain effective Hamiltonians
available in the relevant literature are used. These Hamiltonians include
staggered potential and exchange interaction due to ferromagnetic substrates.
Tunnelling in the systems under consideration is then spin-dependent. The main
focus is on Klein tunnelling and also on the group delay and the associated
Hartman effect. The impact of a gap induced in the spectrum at the Dirac points
on tunnelling is analysed in detail.
