Published online by Cambridge University Press: 02 July 2020
Traditional electron microscopy techniques for imaging magnetic microstructure include out-of-focus Fresnel or Lorentz imaging, Foucault imaging and differential phase contrast (DPC). Off-axis electron holography provides access to both the amplitude and phase of the electron wave which has passed through the sample and therefore can provide direct, quantitative information about the in-plane component of the magnetic induction. The Philips CM200-FEG microscope which was used for the holography described here is equipped with a powerful mini-lens below the specimen enabling 2nm spatial resolution and only a small residual field at the sample. The combination of high coherence and increased magnification enable quantitative mapping of magnetic induction at the nanometer scale.
Electrostatic or magnetic potentials give rise to phase shifts in the holographic interference fringes which can be quantified following reconstruction. In the presence of a magnetic field, the phase equation (for constant composition and neglecting diffraction effects) becomes: