  Starting from the governing equations for a quantum magnetoplasma including
the quantum Bohm potential and electron spin-1/2 effects, we show that the
system of quantum magnetohydrodynamic (QMHD) equations admit rarefactive
solitons due to the balance between nonlinearities and quantum
diffraction/tunneling effects. It is found that the electron spin-1/2 effect
introduces a pressure-like term with negative sign in the QMHD equations, which
modifies the shape of the solitary magnetosonic waves and makes them wider and
shallower. Numerical simulations of the time-dependent system shows the
development of rarefactive QMHD solitary waves that are modified by the spin
effects.
