Electron phase microscopy of FeCo magnetic nanoparticles

Magnetic properties of nanoscale materials are of fundamental interest for both basic research and technological applications. However, the quantitative magnetic characterization at the nanometer scale is experimentally challenging due to the extreme requirements in terms of spatial resolution and sensitivity to small magnetic fields. Transmission Electron Microscope (TEM) is a powerful tool for the structural and physical characterization of materials at the micro and nanoscale. A TEM technique called off-axis electron holography provides us with the unique opportunity of measuring the elusive phase of the electron wave after interactions with a specimen. This enables the quantitative investigation of the local electric and magnetic properties of nanoscale materials. Electron holography is applied to study the magnetic properties of FeₓCoᵧO_z nanoparticles and nanochains, revealing distinct magnetic responses. Holograms encode the phase modulation of the electron wave function through an interference pattern established by the action of an electron biprism. This phase information, related to electric and magnetic potentials, is then extracted from the data with a well-established FFT based algorithm. After separating the electric and magnetic contributions to the phase, we evaluate the magnetic moment of the nanoparticles, or the flux carried by nanochains with data analysis supported by modelling and image simulations. The comparison between experimental and simulated data shows good agreement, provides important information about the investigated nanostructures and allows a better qualitative and quantitative magnetic characterization of their properties.