Elastic Constants of Crystals from X-ray Coherent Scattering Data. Dedicated to Professor Hermann NEELS on the occasion of his 80th birthday

The X-ray diffraction method for determining the elastic constants C_ij and their temperature dependence using the Bragg reflection intensity is discussed.     

Character of indirect exchange interactions in lanthanum manganite

Using the neutron diffraction and magnetic studies a model for exchange interactions in lanthanum manganite with altering ranges having antiferromagnetic and ferromagnetic ordering in the crystal structure is suggested. The anisotropic exchange interaction of the Mn³⁺  O²⁻  Mn³⁺ type, accompanied by the local Jahn-Teller oxygen octahedron distortions, dominates in antiferromagnetic ranges, while in the ferromagnetic ones there are two types of positive exchange interactions: Mn³⁺  O²⁻  Mn⁴⁺, the mechanism of which has been proposed by Zener, and Mn³⁺  O²⁻  Mn³⁺ without the local Jahn-Teller distortions.