Towards an unambiguous electron magnetic chiral dichroism (EMCD) measurement in a transmission electron microscope (TEM)

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The ChiralTEM project (2004-2007) aimed to detect electron magnetic chiral dichroism in a transmission electron microscope, similar to X-ray magnetic circular dichroism. The experiments required single-crystal electron transparent specimens with magnetic induction perpendicular to the specimen's plane. This thesis evaluates various preparation techniques to produce ideal specimens for verifying EMCD. After demonstrating a dichroic measurement, a key method to prove the chiral effect involves inverting the specimen's magnetization from parallel to antiparallel to the electron beam trajectory while keeping other experimental parameters constant. Theoretically, this should result in a change in the measured dichroic signal. In a 300kV TEM's magnetic field, typical ferromagnetic specimens are nearly saturated perpendicular to the specimen's plane. Reversing the current through the objective lens coils will invert the specimen's magnetization, leading to an expected change in any magnetic chiral effect. A switching unit for Tecnai microscopes has been developed to safely manage the lens currents. The direct sensitivity of the dichroic signal to magnetization direction supports the magnetic origin of the observed effect.