  In the presence of anisotropic neutrino and antineutrino fluxes, the quantum
kinetic equations drive coherent oscillations in neutrino helicity, frequently
referred to as spin oscillations. These oscillations depend directly on the
absolute mass scale and Majorana phase, but are usually too transient to
produce important effects. In this paper we present a full momentum-space
analysis of Majorana neutrino spin oscillations in a snapshot of a
three-dimensional neutron star merger simulation. We find an interesting
angular dependence that allows for that resonant and adiabatic oscillations to
occur along specific directions in a large volume of the merger remnant. The
solid angle spanned by these directions is extremely narrow in general. We then
analyze spin transformation in the presence of flavor transformation by
characterizing how the effect's resonance and timescale change during a fast
flavor instability. For this analysis, we derive a generalized resonance
condition that poses a restrictive requirement for resonance to exist in any
flavor channel. We determine that spin oscillations at all locations in the
merger snapshot have a length scale that is too large for significant
oscillations to be expected even where there exist resonant and adiabatic
directions.
