The spontaneous magnetization of nickel

The original data of Weiss and Forrer on nickel are reanalyzed with the aim to obtain a simple empirical relation between the spontaneous magnetization and the temperature both below and above the Curie temperature. A simple relation between the spontaneous magnetization and the temperature is needed to separate easily between the ferromagnetic and the paramagnetic region in the plane given by temperature and field strength, needed for a comprehensive treatment of the magnetocaloric effect (compare J. Biol. Phys. 9, 27 (1981). Various methods of extrapolating to zero magnetic field strength are discussed and used to obtain specified values for the spontaneous magnetization at various temperatures. Starting with a simple expression of cooperativity among elements it is shown that a sufficiently good fit of models to the given data is only obtained with the assumption of three types of cooperativity differing in the intensity of coupling. This intensity of coupling is signified by the magnitude of the exponent in the independent variable (temperature).