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Pierre-Ernest Weiss (25 March 1865, Mulhouse – 24 October 1940, Lyon) was a French physicist who specialized in magnetism. He developed the domain theory of ferromagnetism in 1907. [ 2 ] Weiss domains and the Weiss magneton are named after him.
The idea first appeared in physics (statistical mechanics) in the work of Pierre Curie [6] and Pierre Weiss to describe phase transitions. [7]MFT has been used in the Bragg–Williams approximation, models on Bethe lattice, Landau theory, Curie-Weiss law for magnetic susceptibility, Flory–Huggins solution theory, and Scheutjens–Fleer theory.
In many materials, the Curie–Weiss law fails to describe the susceptibility in the immediate vicinity of the Curie point, since it is based on a mean-field approximation. Instead, there is a critical behavior of the form
The Curie–Weiss law is a simple model derived from a mean-field approximation, this means it works well for the materials temperature, T, much greater than their corresponding Curie temperature, T C, i.e. T ≫ T C; it however fails to describe the magnetic susceptibility, χ, in the immediate vicinity of the Curie point because of ...
He assumed that a given magnetic moment in a material experienced a very high effective magnetic field H e due to the magnetization of its neighbors. In the original Weiss theory the mean field was proportional to the bulk magnetization M, so that = where is the mean field constant. However this is not applicable to ferromagnets due to the ...
The Ginzburg criterion tells quantitatively when mean field theory is valid. It also gives the idea of an upper critical dimension, a dimensionality of the system above which mean field theory gives proper results, and the critical exponents predicted by mean field theory match exactly with those obtained by numerical methods.
1905 – Paul Langevin derives the classical theory for diamagnetism. 1907: Einstein solid model predicts the deviations for the specific heat of solids from Dulong–Petit law. The first theory describing crystallographic defects is developed by Vito Volterra. Pierre Weiss introduces the magnetic domain theory of ferromagnetism.
One of the major discoveries in the study of critical phenomena is that mean field theory of critical points is only correct when the space dimension of the system is higher than a certain dimension called the upper critical dimension which excludes the physical dimensions 1, 2 or 3 in most cases. The problem with mean field theory is that the ...