A simple system to measure magnetostriction in soft magnetic materials

A direct measurement of strain in magnetostrictive materials yields a meaningful result only if the sample remains saturated and the magnetization is rotated between directions parallel and perpendicular to the measurement direction. A simple way to accomplish this is to use small permanent magnets mounted on a rotating shaft. Within the constraints of the limited available space for a sample, we found it most convenient to use a strain gage to detect small changes in length. With commonly available laboratory equipment we were able to achieve a sensitivity ∼0.03 ppm. There is a loading effect that reduces the apparent magnetostriction if the sample is of comparable size to the strain gage. We showed that for a typical nanocrystalline ribbon sample this correction could be experimentally estimated and was of order 20%.