Accession Number : AD0284300

Title :   MAGNETISM AND CRYSTAL STRUCTURE IN NONMETALS

Corporate Author : MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB

Personal Author(s) : GOODENOUGH,J.B.

Report Date : 15 MAY 1962

Pagination or Media Count : 1

Abstract : The magnetic properties of matter are primarily determined by crystal structure and the number of outer electrons on the metal atoms. After a brief description of the principal structures of nonmetallic, magnetic materials, there is a discussion of the two most widely used descriptions of outer electrons in solids: the collectiveelectron description of band theory and the localized-electron description of ligand-field theory. A numerical estimate of the critical separation Rc for transition-metal atoms is given, in which the collective-electron picture is more appropriate for R < Rc and the localizedelectron description is better for R > Rc. Octahedral vs tetrahedral site-preference energies of transition-metal cations play an important role in spinels and garnets - ferrimagnetic materials in wide use in practical applications. The present state of theoretical site-preference energies is critically reviewed, and it is pointed out that failure to account properly for anion polarizations has led to incorrect quantitative conclusions, which have been previously predicted on a point-charge ligand-field model. Since the melting point Tmp of a transition-metal compound is primarily determined by the outer s-p electrons, there may be a transition temperature Tt < Tmp below which there is d electron ordering. Such ordering is usually reflected in both the crystallographic and magnetic properties of these materials. Nine types of electron ordering at a Tt < Tmp are identified and briefly discussed. (Author)

Descriptors :   *CRYSTAL STRUCTURE, *CRYSTALS, DEFORMATION, DISTORTION, ELECTRONS, MINERALS, SOLIDS, THEORY

Distribution Statement : APPROVED FOR PUBLIC RELEASE