Magnetic correlations in paramagnetic iron

A method is described for calculating the extent of short-range order (SRO) in the paramagnetic state of magnetic transition metals. An energy V is calculated for a set of configurations of the exchange field. An entropy S is attached to each configuration; this is the logarithm of the number of configurations with the same degree of long- and short-range magnetic order. The SRO is then found by minimizing the resulting free energy V-TS with respect to a near-neighbour correlation. The resulting Curie temperature Tc and the magnetic entropy are in good agreement with experiment. The corresponding nearest neighbour correlation is small (approximately cos 74°) at Tc.