Magnetostriction of polycrystalline Fe–Ge alloys

The longitudinal and transverse magnetostriction and microstructure of polycrystalline Fe100−xGex (x = 8, 12, 15, 20) alloys were investigated in order to correlate the magnetostriction with microstructure. In order to obtain different microstructures in the Fe100−xGex alloys, the samples were annealed at 600 °C during 2 h and at 1150 °C for half hour and then quenched in cold water. For Ge concentrations lower than 14 at.%, the longitudinal magnetostriction is positive and increases positively up to 22 ppm at 12 at.% Ge then decreases and vanishes at about 14 at.% Ge. For further Ge concentration increase the longitudinal magnetostriction is negative and reaches −30 ppm for Fe80Ge20. This behavior, that is very similar to that reported for Fe–Si alloys, is explained by the structural changes caused by different thermal histories of the alloys.