3He neutron spin filters and zero-field polarimeters are being intensively developed in order to better investigate exotic magnetic systems and prepare the construction of polarized neutron instruments at spallation neutron sources. There are several incentives for using 3He spin filters. They are simple transmission devices having minimal impact on the optics of the neutron beam and they are broadband with properties that vary only weakly with neutron energy. However, a very homogeneous magnetic field is required for long relaxation time of the 3He polarization. We will present devices which remove this difficulty, even in front of a cryomagnet producing a large inhomogeneous stray field.
With a zero-field polarimeter Cryopad, the three components of the scattered spin-polarization vector are measured, which is not possible by standard uniaxial polarization analysis. In the case of magnetic structures, Cryopad allows the direct determination of the direction and phase of the magnetic interaction vector. Hence, it is the most powerful tool for solving non-trivial antiferromagnetic structures. In recent years, the technique has been used to correct major errors in magnetic structures previously determined with other techniques. Efforts are being made to adapt this technique to the case of a spallation neutron source.