Theories of ferromagnetism

Bloch, F., 1929, The Electron Theory of Ferromagnetism and Electrical Conductivity , Z. Physik, 57, 545. 

A. Aharoni, Introduction to the Theory of Ferromagnetism , University Press, Oxford, 1996. 

A. Aharoni, "Introduction to the Theory of Ferromagnetism", Oxford University Press, New York 1996. 

The mean-field equation will be derived from two models the uniform interaction model and the Ising model. Neither of the two derivations depend explicitly on spin. They will be applied to the freeon theory of ferromagnetism Section 6 and freeon theory of high-Tc superconductivity in Section 7. 

In this section we give the freeon theory of ferromagnetism. As pointed about above ferromagnetism is a second order-phase change which is well-defined by mean-field theory. In Section 6.2 we give the uniform interaction derivation of mean-field theory and in Section 6.3 we compare prediction with observation. 

Note that the undoped cuprate is an antiferromagnet and that doping converts it into a superconductor. We have shown above that antiferromagnetic behavior arises from the z = +1 side of the extended Hiickel-Hubbard spectrum in Fig. 4.1. In the ISB theory the superconducting behavior comes from the z = -1 side of Fig. 4.1 just as does the freeon theory of ferromagnetism. 

The freeon theory of ferromagnetism is based on the negative-U, Hiickel-Hubbard Hamiltonian (NUHH). However the conventional positive-U, Hiickel-Hubbard (PUHH) Hamiltonian employs a positive U which is a measure of the repulsion of a bare pair of electrons on a single site. From whence comes NUHH There are three positions to take with respect to NUHH ... 

Adopt the cavalier attitude of Weiss and claim that the use of NUHH in a theory of ferromagnetism "is supported by a sufficient number of facts that one can be certain that it contains an important part of the truth and that... 

The obtained spectra can be explained in the limits of the phenomenological resonance equations for highly anisotropic ferromagnets [14]. Such features are characteristic for imiaxial anisotropy, which rises from the deviation of nanoparticles shape from spherical. The resonance frequency (o of spherical nanoparticles according to the theory of ferromagnetic resonance is determined by the following equation ... 

Jambor JL, Dutrizac JE (1998) Occurrence and constitution of natural and synthetic ferrihydrite, a widespread iron oxyhydroxide. ChemRev 98 2549-2585 files DC, Atherton DL (1984) Theory of ferromagnetic hysteresis (invited). J Appl Phys 55 2115-2120 Jones DH, Srivastava KKP (1989) A re-examination of models of superparamagnetic relaxation. J Magnet Magnetic Mater 78 320-328... 

A. Aharoni Introduction to the theory of ferromagnetism, Second edition... 

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