Magnetic Pendellösung effects in neutron scattering by perfect magnetic crystals

Pendellösung effects in magnetic neutron scattering by thin (thickness of the order of the extinction length) crystals of weak ferromagnets FeBO₃ and α-Fe₂O₃ were investigated. Dynamical oscillations in the scattering intensity dependences on the crystal's effective thickness, temperature and magnetic field orientation have been found. The influence of irregularities in the magnetic structure related to domains, a magnetic phase transition and magnetoelastic oscillations on the Pendellösung oscillation amplitude has been established. The oscillation amplitude and the scattering intensity dependence on the structure-factor magnitude have been used to obtain information on small deformations from perfection of the crystalline and magnetic structures, which are difficult to detect by other methods.