High-temperature magnetostriction in polycrystalline Fe-Co alloys

The saturation magnetostriction of commercial, polycrystalline sheet samples of Fe-Co alloys containing 15, 27, and 50 wt% Co has been measured from room temperature to 700°C, using a laser beam plus photodiode method. All three alloys show substantial magnetostriction at the highest measured temperature. The 27% and 50% Co alloys show a broad maximum in magnetostriction in the temperature range 200°C-400°C, with values reaching 100×10^-6 (100 με). The 50% alloy shows large changes in magnetostriction after the first heating cycle, which are attributed to an increase in the degree of chemical ordering. The magnetostriction in this alloy also depends on the direction of measurement relative to the rolling direction of the sheet.