Observation of pendellösung effect in polarized neutron scattering from a magnetic crystal

Abstract

We have obtained what we believe to be the first experimental evidence, in neutron diffraction from a magnetic crystal, of the Pendellösung effect predicted by a dynamical theory [1]. We measured the flipping ratio R = I +/ I − for polarized neutrons as a function of wavelength for the 2 2 0 reflection from a carefully selected single crystal of yttrium iron garnet (YIG), in which the main crystal defects, the growth striations were parallel to the (112) surface of the 0.48 mm thick sample and therefore inoperative in the symmetrical Laue geometry we used. By using wavelength between 0.4 and 1.1 Å, we obtained a characteristic oscillating behavior of R(λ), which can be related to the oscillations expected for I +(λ) and I −(λ) we chose, where the magnetization, saturated along [111 ] , was perpendicular to the scattering vector. The measured period is not in conflict with the structure factors found via extinction corrections to the kinematical scattering approximation by Bonnet et al. [3]. The amplitude of the measured oscillation, smaller than indicated by calculations based on the above values, is indicative of small deviation from apparent perfection in our crystal; Kato's recent theory of extinction [3] may make it possible to derive more quantitative information on the lattice distortion involved.