  The behaviour of a Dirac electron in graphene, under magnetic fields which
are orthogonal to the layer, is studied. The initial problem is reduced to an
equivalent one, where two one-dimensional Schr\"{o}dinger Hamiltonians
$H^{\pm}$ are intertwined by a first order differential operator. Special
magnetic field are initially chosen, in order that $V^{\pm}$ will be shape
invariant exactly solvable potentials. When looking for more general first
order operators, intertwining $H^-$ with a non-necessarily shape invariant
Hamiltonian, new magnetic fields associated also to analytic solutions will be
generated. The iteration of this procedure is as well discussed.
