  The Kelvin-Helmholtz cooling epoch, lasting tens of seconds after the birth
of a neutron star in a successful core-collapse supernova, is accompanied by a
neutrino-driven wind. For magnetar-strength ($\sim10^{15}$ G) large scale
surface magnetic fields, this outflow is magnetically-dominated during the
entire cooling epoch.Because the strong magnetic field forces the wind to
co-rotate with the protoneutron star,this outflow can significantly effect the
neutron star's early angular momentum evolution, as in analogous models of
stellar winds (e.g. Weber & Davis 1967). If the rotational energy is large in
comparison with the supernova energy and the spindown timescale is short with
respect to the time required for the supernova shockwave to traverse the
stellar progenitor, the energy extracted may modify the supernova shock
dynamics significantly. This effect is capable of producing hyper-energetic
supernovae and, in some cases, provides conditions favorable for gamma ray
bursts. We estimate spindown timescales for magnetized, rotating protoneutron
stars and construct steady-state models of neutrino-magnetocentrifugally driven
winds. We find that if magnetars are born rapidly rotating, with initial spin
periods ($P$) of $\sim1$ millisecond, that of order $10^{51}-10^{52}$ erg of
rotational energy can be extracted in $\sim10$ seconds. If magnetars are born
slowly rotating ($P\gtrsim10$ ms) they can spin down to periods of $\sim1$
second on the Kelvin-Helmholtz timescale.
