The effect of hydrogen on the magnetic properties of Fe-Ni base Invar alloys

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Abstract
The effect of absorbed hydrogen on the magnetic structure of FCC iron-nickel base Invar alloys was studied by means of the 57Fe Mossbauer effect. As the electrolytic hydrogenation proceeded, hydride phases of the same FCC type as the matrix were formed and the characteristic absorption of the Mossbauer spectrum with low field components, which is believed to be an origin of the Invar effect of these alloys, was drastically changed to a simple strong ferromagnetic one. By further hydrogenation, however, the internal field of the hydride phase became smaller. This effect of hydrogen on the magnetic structure of Invar alloys was interpreted in terms of Stoner's band model or more rigorously, a flexible band model with the local bonding state induced by hydrogen. The observed increase of the thermal expansion coefficient of Invar alloys by hydrogen was accounted for in the same way.