Spontaneous volume magnetostriction of invar alloys

Formulations for spontaneous and forced volume magnetostriction and magnetic contribution to thermal expansion are given based on the itinerant electron model of ferromagnetism and by assuming that the change in volume of the system affects the bandwidth and the effective exchange interaction while the shape of the density-of-states curve remains unchanged. Applying the formulas to a step-type density-of-states curve, which we regard as the simplest one holding the most essential character of a 3d band of fcc transition metals, the spontaneous volume magnetostriction at 0 K and the magnetic contribution to thermal expansion in fcc Fe-Ni and Ni-Cu alloys are calculated.