  We present a detailed derivation of a model to study effects of
self-gravitation from semi-classical gravity, described by the
Schr\"odinger-Newton equation, employing spin superposition states in
inhomogeneous magnetic fields, as proposed recently for experiments searching
for gravity induced entanglement. Approximations for the experimentally
relevant limits are discussed. Results suggest that spin interferometry could
provide a more accessible route towards an experimental test of quantum aspects
of gravity than both previous proposals to test semi-classical gravity and the
observation of gravitational spin entanglement.
