https://phys.org/news/2018-07-non-magnetic-steel-magnetism.html

Engineers from the TUK and physicists from the Johannes Gutenberg-University Mainz (JGU) are presenting a solution in their current study. Their technique makes use of magnetic effects, even though it is being applied to non-magnetic material. "With magnetic steel, it is possible to find changes in the structure early on," explains the doctoral student from Kaiserslautern Shayan Deldar. "Even tiny deformations change the magnetic properties. This can be measured with special sensor technology."

The researchers have coated a non-magnetic steel with magnetic films, each 20 nanometer thin, consisting of terfenol-D, an alloy comprising the chemical elements terbium, iron and dysprosium, or permalloy, a nickel-iron compound. The researchers then used a so-called Kerr microscope to check whether strains in the steel could be detected in the microscopic range. "This is achieved using the so-called Kerr effect," explains Smaga, "which allows the magnetic microstructures, the so-called domains, to be imaged by rotating the polarization direction of light."