  In neutron interferometric experiments using polarized neutrons coherent
spin-rotation control is required. In this letter we present a new method for
Larmor spin-rotation around an axis parallel to the outer guide field using
topology optimized 3D printed magnets. The use of 3D printed magnets instead of
magnetic coils avoids unwanted inductances and offers the advantage of no heat
dissipation, which prevents potential loss in interferometric contrast due to
temperature gradients in the interferometer. We use topology optimization to
arrive at a design of the magnet geometry that is optimized for homogeneity of
the magnetic action over the neutron beam profile and adjustability by varying
the distance between the 3D printed magnets. We verify the performance in
polarimetric and interferometric neutron experiments.
