  Millisecond pulsars are old neutron stars that have been spun up to high
rotational frequencies via accretion of mass from a binary companion star. An
important issue for understanding the physics of the early spin evolution of
millisecond pulsars is the impact of the expanding magnetosphere during the
terminal stages of the mass-transfer process. Here I report binary stellar
evolution calculations that show that the braking torque acting on a neutron
star, when the companion star decouples from its Roche-lobe, is able to
dissipate >50% of the rotational energy of the pulsar. This effect may explain
the apparent difference in observed spin distributions between x-ray and radio
millisecond pulsars and help account for the noticeable age discrepancy with
their young white dwarf companions.
