Mapping spatial and field dependence of magnetic domain memory by soft X-ray speckle metrology.

The occurrence of magnetic domain memory has been observed in ferromagnets, either induced by structural defects or by exchange couplings. Being able to quantify the amount of memory as a function of length scale, field and temperature is both of fundamental and technological importance. A technique has been refined to statistically quantify the magnetic domain memory in ferromagnetic thin films by using coherent soft-X-ray scattering metrology. This technique, based on cross-correlating magnetic speckle patterns, provides a unique way to map out the behavior of domain memory. Here, the details of our correlation method and the necessary treatment of the X-ray scattering images to extract spatial and field dependences in the memory information are reviewed. The resulting correlation maps, measured on [Co/Pd]IrMn multilayers, show how magnetic domain memory evolves at various spatial scales, as a function of the field magnitude throughout magnetization cycles, but also as a function of field cycling and of temperature. This technique can easily be applied to a wide variety of systems presenting memory effects, in soft and hard matter, and also to dynamical studies.