MAGNETISM AND CRYSTAL STRUCTURE IN NONMETALS
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)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 15, 1962
- Accession Number
- AD0284300
Entities
People
- J.b. Goodenough
Organizations
- Massachusetts Institute of Technology