Extinction effects in neutron scattering from single magnetic crystals

Abstract

Results arising from the treatment of magnetic scattering of neutrons, taking due account of the possibility of polarization of the neutron beam, indicate that the usual expressions for primary and secondary extinction must be modified in certain cases. Extinction, particularly primary extinction, will be generally more severe for reflections which have both nuclear and magnetic contributions than for either pure nuclear or pure magnetic reflections. Formulas and curves are presented for primary and secondary extinction corrections which are applicable to both magnetized and unmagnetized ferromagnetic or antiferromagnetic crystals. Some of the results obtained may be conveniently used to determine relative amounts of primary and secondary extinction, and consequently both mosaic block size and angnlar distribution. Many of the calculations are of interest in predicting the effects of extinction on experiments designed either to produce or use polarized neutron beams. The precession of the neutron polarization axis about the magnetic axis can affect the reflected intensity if extinction is severe. This effect is discussed briefly and is shown to be serious only for magnetized crystals. The appendix discusses the necessary changes in the scattering formulas if all the spins in the unit cell do not lie along a unique magnetic axis.more » (auth)« less