  We present a rigorous theoretical framework underpinning the technique of
spin-echo modulated small-angle neutron scattering (SEMSANS), and show how the
technique can be extended in order to generate spin-textured neutron beams with
orbital angular momentum (OAM) via birefringent neutron spin-polarization
devices known as magnetic Wollaston prisms. Neutron OAM beams are
mathematically characterized by a ``cork-screw'' phase singularity $e^{i \ell
\phi}$ about the propagation axis where $\ell$ is the OAM quantum number. To
understand the precise relationship between the emergent OAM state and the
variety of spin textures realized by various setups, we have developed a
path-integral approach that in the interferometric limit makes a judicious use
of magnetic Snell's law. We show that our proposed technique produces a complex
two-dimensional pattern of spin-OAM entangled states which may be useful as a
probe of quantum magnetic materials. We compare our path-integral approach to
the well-known single-path Larmor precession model and present a pedagogical
derivation of magnetic Snell's law of refraction for both massive and massless
particles based on Maupertuis's action principle.
