Electron knock-on damage effects on electron magnetic chiral dichroism of magnetic metals using cobalt as a model

Abstract

Electron magnetic chiral dichroism (EMCD) is a high-resolution technique currently in development for quantitative magnetic measurements using transmitted electrons. However, the inevitable electron damage to materials can be a significant yet easily overlooked factor affecting the quantification accuracy. This work experimentally investigated the electron knock-on damage effects on EMCD of magnetic metals using metallic cobalt as a model. Three issues are involved in the metal-surface damage process. It was revealed that under sustained electron irradiation during spectra acquisition, gradual removal of the thin surface oxidation layer, rather than a simple continuous thickness reduction that changes the diffraction and plural scattering conditions, can lead to notable residual nonmagnetic components in EMCD spectra and may make the quantified result of the orbital-to-spin moment ratio remarkably higher than the actual value. It was, thus, proposed to pay great attention to the surface oxidation and to minimize the effect of the oxidation layer by performing electron irradiation on the target area prior to EMCD experiments. A further experiment was additionally proposed to quantify the impact of thickness reduction on the magnetic components of momentum-resolved electron energy-loss spectra and the EMCD quantification. This study advances the application of EMCD in magnetic metals.