Element-selective X-ray detected magnetic resonance: a novel application of synchrotron radiation.

X-ray detected magnetic resonance (XDMR) is a new element-selective spectroscopy in which X-ray magnetic circular dichroism is used to probe the resonant precession of spin and orbital magnetization components when a strong microwave pump field is applied perpendicularly to the static bias field. Experimental configurations suitable for detecting the very weak XDMR signal are compared. XDMR signatures were measured in yttrium iron garnet and related thin films on exciting not only the iron K-edge but also the yttrium at diamagnetic sites. These measurements are shown to yield unique information regarding the wide-angle precession of induced magnetization components involving either orbital p-projected densities of states at the iron sites, or spin polarized d-projected densities of states at the yttrium sites. Extending XDMR measurements into the millimeter wave range would make it possible to study paramagnetic systems routinely and investigate optical modes as well as acoustic modes in ferrimagnetic/antiferromagnetic systems.

Advanced detection systems for X-ray fluorescence excitation spectroscopy.

This paper accounts for selected detector developments carried out over the past 15 years within the ESRF X-ray Absorption Spectroscopy group. This includes various types of photodiodes used as integrated current detectors. Special emphasis is put on the long-standing development of a Si drift-diode array suitable for energy-dispersive detection of X-ray fluorescence. This detector, which is now operational, was used to record high-quality XMCD/XAFS spectra on [Fe70Pt30] nanoparticles highly dispersed on a Si wafer. Using numerically deconvoluted spectra, energy resolution was decreased to 82 eV for the Si Kalphabeta line, 126 eV for the Fe Kalpha line and 176 eV for the Pt Lalpha line. A high-vacuum-compatible high-energy-resolution crystal analyzer was also installed on ID12, making it possible to record X-ray fluorescence excitation spectra in the photon-in/photon-out mode over a wide spectral range. Prospects of adapting these methods in order to investigate biological samples are briefly discussed.