The recent progress in instrumentation guarantees that ELNES will rest a strong competitor of XANES in spite of the improved spatial resolution seen with synchrotrons. Up to now there was however one application uniquely reserved for synchrotrons: X-ray magnetic circular dichroism (XMCD). Recently it was shown that contrary to intuition XMCD can well be measured with inelastic electron scattering [1]. In analogy to XMCD we introduced the term ELMCD: Energy Loss Magnetic Chiral Dichroism. We choose the adjective chiral instead of circular in order to stress that there is no (circular) polarization of the probe electron involved. Rather, it is the chirality of the allowed transitions that is detected in the inelastic electron scattering experiment. In the experiment, a coherent superposition of two momentum transfer vectors perpendicular to each other is set up, tuning the phase difference between the two interactions to p/2. The inelastic interference term carries then the dichroic signature. The proper tool for description of inelastic interference, and as such also for ELMCD is the mixed dynamic form factor (MDFF). More precisely, it turns out that the signature of ELMCD is contained in the imaginary part of the MDFF. In the dipole approximation, a particularly simple expression is obtained. An overview of the present situation of the CHIRALTEM project is given, including several possible experimental setups to measure the dichroic signal with electrons (Bloch wave interferometry, biprism in the C2-aperture, and double crystal interferometry). We report also on attempts to manipulate the magnetic field in the specimen by a dedicated holder, as is needed for ELMCD. Simulation of the Ni and Fe ELMCD based on a modified version of the WIEN2k package are discussed. We present also the first successful comparison of ELMCD with XMCD, obtained in a TEM and in a synchrotron, performed with the same specimen. References [1] C. Hébert, P. Schattschneider, Ultramicroscopy 96 (2003) 463. [2] This research was supported by the European Commission, contract nr. 508971 (CHIRALTEM).
Circular dichroic experiments with electrons - recent results of the CHIRALTEM project
E Carlino;
2005
Abstract
The recent progress in instrumentation guarantees that ELNES will rest a strong competitor of XANES in spite of the improved spatial resolution seen with synchrotrons. Up to now there was however one application uniquely reserved for synchrotrons: X-ray magnetic circular dichroism (XMCD). Recently it was shown that contrary to intuition XMCD can well be measured with inelastic electron scattering [1]. In analogy to XMCD we introduced the term ELMCD: Energy Loss Magnetic Chiral Dichroism. We choose the adjective chiral instead of circular in order to stress that there is no (circular) polarization of the probe electron involved. Rather, it is the chirality of the allowed transitions that is detected in the inelastic electron scattering experiment. In the experiment, a coherent superposition of two momentum transfer vectors perpendicular to each other is set up, tuning the phase difference between the two interactions to p/2. The inelastic interference term carries then the dichroic signature. The proper tool for description of inelastic interference, and as such also for ELMCD is the mixed dynamic form factor (MDFF). More precisely, it turns out that the signature of ELMCD is contained in the imaginary part of the MDFF. In the dipole approximation, a particularly simple expression is obtained. An overview of the present situation of the CHIRALTEM project is given, including several possible experimental setups to measure the dichroic signal with electrons (Bloch wave interferometry, biprism in the C2-aperture, and double crystal interferometry). We report also on attempts to manipulate the magnetic field in the specimen by a dedicated holder, as is needed for ELMCD. Simulation of the Ni and Fe ELMCD based on a modified version of the WIEN2k package are discussed. We present also the first successful comparison of ELMCD with XMCD, obtained in a TEM and in a synchrotron, performed with the same specimen. References [1] C. Hébert, P. Schattschneider, Ultramicroscopy 96 (2003) 463. [2] This research was supported by the European Commission, contract nr. 508971 (CHIRALTEM).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
