ORIGIN OF EFFECTIVE FIELDS IN MAGNETIC MATERIALS
The origin of the effective magnetic fields at the nuclei ar magnetic resonance, electron paramagnetic resonance, specific heat, and nuclear polarization methods is investigated theoretically by means of the exchange polarization mechanism. Exchange-polarized iron series Hartree-Fock calculations were carried out for free ions and neutral atoms, ions in a (crude) crystalline field (as in a salt), and spin densities and configurations which conform with energy band and neutron magnetic scattering observations for the ferromagnetic metals. The effective field data for metals, ferrites, rare-earth garnets, and salts are then discussed and it is shown that the dominant contribution to the effective field (in almost every case) arises from the (exchange) polarization of the core electrons by the spin density of the unpaired outer electrons. For the transition metals, the role of the conduction electrons is analyzed including some new contributions not previously considered. The data for ions like Fe/sup 3+/ and Mn/sup 2+/ may be understood mainly on the basis of the core polarization term but such factors as covalent bonding, charge transfer, crystal field effects (such as distortions from cubic symmetry) must also be included. For ions like Fe/sup 3+/ and Co/sup 2+/ the (large) field due to unquenched orbital angular momentum must also be considered and several cases in which the orbital field dominates are discussed. The exchange polarization method and the accuracy of the analytic spinpolarized Hartree-Fock functions are discussed with regard to the sensitivity of the internal field to orbital descriptions, the effect of crystalline environments, and to expansion and contraction of the spin density. Each factor is investigated in detail by means of accurate exchangepolarized calculations. In conjunction with these studies a restricted Hartree-Fock calculation for Mn/sup 2+/ was carried out (and is reported as an Appendix) which is more accurate than existing calculations and indicates the accuracy of earlier analytic Hartree-Fock calculations. (auth)
- Research Organization:
- Avco, RAD. Wilmington, Mass.
- NSA Number:
- NSA-15-031414
- OSTI ID:
- 4840405
- Journal Information:
- Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D, Vol. Vol: 123; Other Information: Orig. Receipt Date: 31-DEC-61
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ATOMIC MODELS
ATOMS
BINDING ENERGY
COBALT
CRYSTALS
ELECTRIC CHARGES
ELECTRIC CONDUCTIVITY
ELECTRONS
ENERGY LEVELS
FERRITES
FERROMAGNETIC MATERIALS
HARTREE-FOCK METHOD
IONS
IRON
MAGNETIC FIELDS
MAGNETIC MATERIALS
MAGNETISM
MANGANESE
METALS
MOESSBAUER EFFECT
MOMENTUM
NEUTRONS
NUCLEAR MAGNETIC RESONANCE
NUCLEI
NUMERICALS
ORBITS
PARAMAGNETISM
POLARIZATION
QUANTUM MECHANICS
RARE EARTHS
SALTS
SCATTERING
SPECIFIC HEAT
SPIN