THEORY OF DIRECT EXCHANGE IN FERROMAGNETISM

Abstract

An extensive investigation is presented on the role of direct exchange as the mechanism responsible for ferromagnetism. The direct exchange integral J which arises in Heisenberg's theory of ferromagnetism and which bas been a subject of considerable speculation and controversy (particularly concerning its sign behavior as a function of internuclear separation) is considered for several cases for which (as Lowdin has shown) J is rigorously defined. (1) A pair of atoms with a single electron per atom (the hydrogenic case). J is calculated for the unrealistic but historically interesting case or hydrogen 3d functions and the computationally more difficult case of the exchange between 3d orbitals for the iron series elements. The fact that the iron series 3d orbitals are not eigenfunctions of the free atom (hydrogenic) hamiltonian is shown to profoundly affect the results. Calculations for all pairs of 3d orbitals show that J is sensitive to the angular dependence or the wave functions (and the precise closed radial shape as well). (2) A single hole in otherwise shells (such as a pair or iron series atoms in the 3d9 configuration). The effect on J of "clothing" the atoms with the remaining electrons is discussed first with regard to the effect of the core electrons on the one-electron potentials and secondly with respect to the effect of the overlap of the core electrons. (From an analysis of these terms it is suggested that the paired "4s" conduction electrons of the metal can play an important role in "direct exchange", quite aside from a Zener type of effect). We find that the direct exchange parameter J is large and negative for the two electron case {case (1)} and negative, but smaller, for the "clothed" 3d9 case {case(2)}, whereas for ferromagnetism it should be positive.

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Document Details

Document Type
Technical Report
Publication Date
Jul 01, 1961
Accession Number
AD0267668

Entities

People

  • A. J. Freeman
  • R. E. Watson

Organizations

  • United States Army Research Laboratory

Tags

Communities of Interest

  • Energy and Power Technologies
  • Weapons Technologies

DTIC Thesaurus Topics

  • Atomic Orbitals
  • Atomic Structure
  • Atoms
  • Eigenvectors
  • Energy Bands
  • Ferromagnetism
  • Governments
  • Ground State
  • Jet Propulsion
  • Magnetic Materials
  • Magnetic Properties
  • Materials
  • Munitions
  • Perturbation Theory
  • Perturbations
  • Quantum Numbers
  • Quantum Properties

Fields of Study

  • Physics

Readers

  • Quantum spin resonance or Electron Paramagnetic Resonance spectroscopy.
  • Theoretical Analysis.

Technology Areas

  • Microelectronics
  • Space