Task: Text Categorization
Input (English): The strength of this phenomenon in an atom is proportional to a function containing a "hyperbolic cotangent of x over 2J" term; that function is the Brillouin function, which is replaced in the classical formulation by the Langevin function. Second order perturbation theory includes a variety of this phenomenon named for Van Vleck, and the spin of free electrons on a crystal lattice causes a variant of this phenomenon named for (*) Pauli. In certain materials experiencing this phenomenon, the susceptibility is given by "C over (T minus T sub c)," and the susceptibility is inversely proportional to absolute temperature according to Curie's Law. This phenomenon occurs above the Neel temperature as well as above the Curie temperature, and it is caused by the aligning of dipoles. For 10 points, name this weak form of magnetism only present in an external magnetic field.
Output (English): Science