Characterization of Heusler crystals for polarized neutrons monochromators

Single crystals of Heusler alloy Cu(2)MnAl are widely used to construct efficient focusing monochromators for polarized neutrons. Very large monocrystalline ingots of length 150 mm and diameter 60 mm have been grown with success at ILL during the last two years. A brief study of the quality of such ingots by neutron diffraction at wavelength lambda = 1.8 Angstrom is presented. We are able to produce large monograin slabs of dimensions 100 x 17 x 5 mm(3) whose (1 1 1) reflection is characterized by a width (FWHM) of 0.35 degrees, a peak reflectivity of about 30% (unmagnetised state) and a flipping ratio close to 40. (C) 1999 Elsevier Science B.V. All rights reserved.