  The afterglow emission of some gamma-ray bursts (GRBs) show a shallow decay
(plateau) phase implying continuous injection of energy. The source of this
energy is very commonly attributed to the spin-down power of a nascent
millisecond magnetar. The magnetic dipole radiation torque is considered to be
the mechanism causing the spin-down of the neutron star. This torque has a
component working for the alignment of the angle between rotation and magnetic
axis, i.e., inclination angle, which has been neglected in modelling GRB
afterglow light curves. Here, we demonstrate the evolution of the inclination
angle and magnetic dipole moment of nascent magnetars associated with GRBs. We
constrain the initial inclination angle, magnetic dipole moment and rotation
period of seven magnetars by modelling the seven long-GRB afterglow light
curves. We find that, in its first day, the inclination angle of a magnetar
decreases rapidly. The rapid alignment of the magnetic and rotation axis may
address the lack of persistent radio emission from mature magnetars. We also
find that in three cases the magnetic dipole moments of magnetars decrease
exponentially to a value a few times smaller than the initial value. The
braking index of nascent magnetars, as a result of the alignment and magnetic
dipole moment decline, is variable during the afterglow phase and always
greater than three.
