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Magnetic DAFS

There have been beautiful recent developments in the use of magnetic circular x-ray dichroism (MCXD) to study magnetic materials [36, 37, 38]. MCXD measurements provide element-specific information about the magnetic environment of an absorbing atom from the difference in the x-ray absorption coefficient for right and left circularly polarized x rays. In just the same way that DAFS is the diffraction analog of XAFS, and provides site-specific local structural information, McDAFS is the diffraction analog of MCXD (viz., McXAFS), and provides site-specific local magnetic information. McXANES and McDANES probe the empty density of magnetic states near threshold. McEXAFS and McEDAFS probe the radial distribution of the magnetization of the atoms surrounding the excited atom [37]. MCXD microscopy has been done [38] with a resolution of about 1 micron by imaging the emitted photoelectrons. McDAFS studies can be done with comparable, or even smaller, spatial resolution using x-ray capillary optics [39]. The first site-separated McDANES results have recently been reported [40].

The primary motivation for doing McDAFS instead of MCXD is to obtain the site-selectivity produced by the crystallographic sensitivities of DAFS. This will allow element-specific and site-specific determinations of the density of magnetic states near threshold (from the McDANES) and of the radial distribution of the magnetic neighbors surrounding the excited atom (from the McEDAFS). McDAFS provides the only way to directly measure the complete, detailed, site-separated, local magnetic environment and properties of specific elements at specific sites. The wavevector selectivity of McDAFS should also prove useful in studies of magnetic multilayers since it will allow the signals from the same element type in the different layers to be separated.