10.1.Molecular Field Inside Matter
Where the integrals extend over all sources: J, and . The molecular field Hm may be expressed in a similiar way, except that now there are additional contributions from the surface of the cavity and from the individual dipoles in the cavity. The integral of (r-r’)/ over the cavity volume need not be excluded specifically, since in the uniformly magnetized specimen. Thus,
Hm = H + Hs + H’
10.2.Origin of Diamagnetism
Fq = me R
Where Fq is the electric force holding the electron to its atom, 0 is the angular frequency of the electron in its orbit, and me is the electron mass. Application of a magnetic field exerts an additional force –ev x Bm on the electron. Asumming that electron stays in the same orbit, we find
Fq RBm = me 2R
10.3.Origin of Paramagnetism
the magnetization is given by
Where N is the number of molecules per unit volume. Except for temperatures near absolute zero, the Langevin function can be approximated by the first term in its power series:
Hm
Which yields the paramagnetic susceptibility
10.4.Theory of Ferromagnetism
and
10.5.Ferromagnetic Domains
According to the preceding section, a ferromagnetic specimen should be magnetized very nearly to saturation (regardless of its previous history) at temperatures below the Curie temperature. This statement appears to be contrary to observation. We know, for example, that a piece of iron can exist in either a magnetized or unmagnetized condition.
10.6.Ferrites
According to the heisenberg theory of ferromagnetism, there is a change in electrostatic energy assosiated with the change from parallel to antiparallel spin alignment and is at the same time of sufficient magnitude, the material composed of these atoms is ferromagnetic. If the energy change favors antiparallel alignment, it is still possible to obtain an ordered spin structure, but with spins alternating from atom to atom as the crystal is traversed.
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