Invar Anomaly

Abstract
The origin of the large volume magnetostriction responsible for the Invar anomaly is discussed with respect to several recent theories. Magnetic and thermal expansivity measurements of Fe–Ni–Mn alloys with constant Ni/Fe ratio of 2/3 indicate qualitative agreement with Zener's theory based on competing exchange interactions. Coercive force (Hc) measurements of an Fe–Ni–Co alloy containing mixed martensite and austenite ferromagnetic phases display a maximum Hc at the Curie temperature (θγ) of the austenite which is known to display the Invar anomaly. The sharp change in the value of Hc at θγ is contrary to theories based on concentration fluctuation.