Curie temperature of alloys,its measurement and technical importance

The basic relations between magnetic saturation and Curie temperature versus the composition is discussed for ferromagnetic metals and alloys of technical importance. There exist a number of methods for the determination of the transition from ferromagnetic to paramagnetic behaviour, i.e. thermogravimetry (thermomagnetometry), inductice methods and calorimetric methods. As most nonmagnetic solute elements lower the Curie temperature of ferromagnetic metals the Curie temperature can be used to determine the concentration of the solute element in binary systems up to the solubility limit. In ternary and higher systems there is a combined effect of different element on the change of Curie temperature. Thus it is not generally possible to use the Curie temperature as a measure of the solute element concentration in such alloys. Under certain circumstances e.g. when the composition of a multiphase material is close to the equilibrium composition, it is still possible to use the Curie temperature to characterize the composition of the ferromagnetic phase. Such a system is exemplified by normal cobalt-based cemented carbide. The Curie temperature can also be used as a means for temperature calibration, e.g. of thermobalances. Certified Reference Materials have been selected for this purpose by the ICTA Committee on Standardization.