Neutron Depolarisation in Zigzag Folded 90 deg Walls in Silicon Iron

A polarized monochromatic ( lambda = 0.16 and 0.41 nm) neutron beam is transmitted at various glancing angles theta (0 < = | theta | < = 10 deg ) through 90 deg walls in a Fe--5Si single crystal of dimensions 40 x 3.2 x 1.9 mm exp 3 with its bar axis parallel to (110). From a three-dimensional polarisation analysis after transmission it appears that the effect of the 90 deg wall on the neutron polarisation vector is presented up to at least | theta | = 10 deg . From these observations it is concluded that the 90 deg wall is not a plane Bloch wall, but rather a wall region with a thickness of at least 10 mu m. This is consistent with the zigzag folding of such walls. Furthermore the technique used enables the mean effects of neighbouring 90 deg walls to be distinguished . In a transmission experiment over the "upper" half of the sample it has been observed that the effect of neighbouring walls on the polarisation vector is antisymmetric in theta . This result supports a suggestion that the amplitude of the zigzag folding varies with the height being in antiphase in neighbouring 90 deg walls. 21 ref.--AA