Keoki Seu Seminar:
With the advent of free electron lasers there has been interest in using coherent x-rays to probe condensed matter systems. Resonant scattering with x-rays allow elemental specificity with magnetic contrast, and coherent light leads to speckle in the scattered pattern due to interference from waves exiting the sample. This is a unique thumbprint of the morphology. This uniqueness allows one to monitor changes in the speckle pattern versus time (called x-ray photon correlation spectroscopy, XPCS) or external field (called return point memory, RPM). I will show applications of coherent x-rays ferromagnetic systems. The first uses XPCS to measure the equilibrium dynamics of a magnetic system as it goes through an order-order spin-reorientation, where the magnetization reorients itself from in-plane to out-of-plane as the temperature is varied. The second are RPM measurements about the statistical configuration of domains during magnetization reversal.
I will also present results on our imaging effort in reflection geometries with coherent x-rays. The development of a technique for imaging in reflection geometry (as opposed to transmission geometries where most x-ray imaging work is done) would allow us to probe buried interfaces and single crystal samples where the scattering vector q that can only be reached in reflection. The method is Fourier transform holography, where the exit wave from a sample interferes with a reference wave, encoding the phase of the exit wave. We have demonstrated the technique on a test pattern and are moving towards implementing it on magnetic systems.
