Electronic structure and lattice constant of invar alloys

A theory of the volume striction in ferromagnetic transition metal alloys is developed on the basis of the Alexander‐Anderson‐Moriya theory of the exchange interaction. The volume derivative of the interaction between a pair of atoms is calculated under the assumption that a volume change affects the state density of the s band and 3d atomic levels. In fcc Ni‐Fe the number of 3d minority spin electrons of a Fe atom increases with increasing Fe concentration. The volume derivative of the interaction between two Fe atoms shows an anomalous dependence on the Fe concentration through the change of the number of 3d minority spin electrons which explains the large spontaneous volume striction, lattice constant anomaly and negative thermal expansion at low temperatures in invar alloys. The possibility of finding Fe atoms with magnetic moment antiparallel to bulk magnetization and its relevance to the lattice anomalies are discussed also.