Measuring strain at the atomic-scale with Differential X-ray Absorption Spectroscopy

The development of smart materials for use in transducer devices has driven considerable research in recent decades. In this field, phenomena such as magnetostriction underpin the operation of sensors and actuators, and energy harvesting devices. Thus, knowledge of their origin and mechanics, and how they manifest themselves in different materials, enables the development of new devices and optimisation of existing technologies. Yet this research is not without its limitations. Theoretical studies naturally describe material properties at a fundamental, atomic-scale. But experimental work struggles to verify such models at a similarly microscopic scale. Saturation strains from typical magnetostrictive materials induce displacements between neighbouring atoms of only a few femtometres. On such a scale, even commonly employed local probes, such as x-ray absorption spectroscopy (XAS), lack the resolution to observe this motion by some two orders of magnitude. As a result, experiments typically employ strain gauges on large, macroscopic samples, where the strain is easier to detect, but where atomic information is lost. However, the recent development of differential XAS (DiffXAS) at the ESRF presents a unique opportunity to bridge this gap between macro-scale experimental work, and fundamental theoretical models [1]. This talk will study the development of DiffXAS via the most significant results obtained to date. These include studies of the important Fe-Ga and Fe-Pt systems, where DiffXAS analysis procedures have allowed chemically-selective, atomic magnetostriction coefficients to be quantified [2][3]; and an investigation of the magneto-elastic coupling of FeCo through measurements under applied hydrostatic pressure [4]. [1] R.F. Pettifer et al., Nature 435, 79 (2005) [2] M. P. Ruffoni et al., Phys. Rev. Lett. 101, 147202 (2008) [3] S. Pascarelli et al., Phys. Rev. B 77, 184406 (2008) [4] S. Pascarelli et al., Phys. Rev. Lett. 99, 237204 (2007)Submitted versio