Changes of Crystal Structure in Antiferromagnetic Compounds

Abstract

A RECENT communication by Selma Greenwald and J. S. Smart¹ has directed attention to the significance of the structural deformations observed by us in monoxides of the transition elements² in relation to their antiferromagnetic behaviour. It is particularly noteworthy that the temperatures at which departure from the high-symmetry face-centred cubic structure cell is first manifest are almost exactly the antiferromagnetic Curie temperatures. It would appear that deformations of the simpler arrangements existing above these Curie temperatures are a natural consequence of the setting of adjacent magnetic atoms in anti-parallel spin orientations below these temperatures. Neutron diffraction work on manganous oxide by Shull³ has shown that the magnetic cell has a lattice constant double that of the elementary structure cell; but it remains for X-rays to demonstrate the change in shape consequent upon the preferential arrangement of the metal atoms.