Magnetic Materials II: Microscopic View
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The physics behind the parallel or antiparallel orientation of two spins is examined within the framework of two neutral hydrogen atoms at a distance r apart. The exchange interaction, J, is defined and calculated. The question of the appearance or not of ferromagnetism or antiferromagnetism within the JM and its extensions is studied. The same question is also examined within the framework of the so-called Hubbard model. The latter for large values of U/ ❘V2❘ is reduced to a simple version of the Heisenberg model, which is used to study the ground state, the excitation spectrum, and the thermodynamics of ferromagnets and antiferromagnets (usually within the framework of the mean field approximation).
KeywordsFermi Surface Ground State Energy Hubbard Model Coulomb Repulsion Heisenberg Model
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- See the Ashcroft and Mermin book [SS75], pp. 672–691 and 701–724.Google Scholar
- A detailed advanced theory of magnetic materials can be found in the books [Ma168] to [Ma173] and [Ma175], [Ma176], [Ma178].Google Scholar
- There is an extensive literature on the Hubbard model [21.10]. A small sample follows: [21.11–21.19].Google Scholar