Magnetism and microstructure at relevant length scales: Complementary measurements with electron and photon probes

The optimization and understanding of the magnetic properties of materials requires a dynamic iteration between synthesis, property measurements and the evaluation/control of microstructure (physical, chemical and magnetic) at the appropriate length scales. There are two length scales that generally determine the properties of materials: the characteristic length associated with the dimensional characteristics of the magnetic phenomenon of interest and the size of the microstructural feature arising from the processing It is important to identify the range where these two length scales overlap, for it is there that novel properties and phenomenon are usually observed. For magnetic materials of both fundamental and technological interest, these length scales can range from the atomic (interfaces) to a few tens of nanometers (grain sizes). Hence, advances in the development of such materials will critically depend on our ability to characterize them by a range of electron-optic and x-ray scattering/dichroism techniques. In this paper, two critical issues, i.e. the role of interfaces in thin films heterostructures and the magnetic domain behavior in nanostructured elements, will be discussed. Energy-filtered imaging techniques, using inner-shell excitations, have been developed to provide a quantitative measurement of roughness in Fe/Cr multilayers and correlated with spin-dependent scattering. Magnetic roughness at interfaces, important in understanding the magnitude of exchange biasing in antiferromagnetic-ferromagnetic bilayers, was measured by x-ray magnetic circular dichroism. Domain structures in patterned magnetic elements were observed by Lorentz imaging their dynamics and reversal behavior was studied by in situ reversal experiments. In transmission electron microscopy, only the in-plane component of the magnetic induction can be measured. To obtain the out-of-plane component, complementary imaging using synchrotron radiation and magnetic dichroism contrast was employed. Details of these experiments, emphasizing the complementarity of such measurements as well as future research directions will be presented.