  G. Srinivasan et al. (1990) proposed a simple and elegant explanation for the
reduction of the neutron star magnetic dipole moment during binary evolution
leading to low mass X-ray binaries and eventually to millisecond pulsars:
Quantized vortex lines in the neutron star core superfluid will pin against the
quantized flux lines of the proton superconductor. As the neutron star spins
down in the wind accretion phase of binary evolution, outward motion of vortex
lines will reduce the dipole magnetic moment in proportion to the rotation
rate. The presence of a toroidal array of flux lines makes this mechanism
inevitable and independent of the angle between the rotation and magnetic axes.
The incompressibility of the flux-line array (Abrikosov lattice) determines the
epoch when the mechanism will be effective throughout the neutron star. Flux
vortex pinning will not be effective during the initial young radio pulsar
phase. It will, however, be effective and reduce the dipole moment in
proportion with the rotation rate during the epoch of spindown by wind
accretion as proposed by Srinivasan et al. The mechanism operates also in the
presence of vortex creep.
