Theory of Invar

A simple theory based on the high-spin, low-spin results of rigid-lattice band calculations for ordered Fe3Ni and the Debye-Grüneisen approximation is presented. The theory qualitatively explains the anomalous temperature dependence of the thermal expansion, bulk modulus, magnetization, and high-field susceptibility, and the different pressure dependencies of the lattice constant at different temperatures of Invar. © 1992.