Scanning Electron Microscopy with Polarisation Analysis

Abstract

The scanning electron microscope with polarization analysis (SEMPA or spin‐SEM) is a powerful tool to investigate the magnetic structure of ferromagnetic surfaces with high spatial resolution. In the article the spin polarized secondary electron emission is described and discussed as the contrast generating process that is utilized in SEMPA. Taking the secondary electron emission from itinerant ferromagnets as starting point, the properties and best case performance of spin‐SEM are derived. The consequences of these properties for the realization of such a microscope and the polarization analyzer, as well as the resulting strengths and weaknesses of the technique are discussed. The best case performance is compared to the actual performance of a newly designed microscope. Several examples for the application of spin‐SEM are presented; e.g. the study of the spin‐reorientation transition in ultrathin films and interlayer exchange coupling. It is shown how a decoration technique can be used to analyze ferromagnets where the surface is non‐magnetic due to contamination or capping by a protective layer. Finally, the influence of sample morphology on the polarization detection and details of the analysis of the vectorial polarization measurement are comprehensively discussed.

Magnetism in ultrathin film structures

“…Besides these techniques, an array of other techniques have been employed in the study of thin magnetic films, in particular, magnetic and surface imaging techniques [352][353][354], including atomic force microscopy (AFM) [355][356][357], magnetic force microscopy (MFM) [358][359][360], scanning tunnelling microscopy (STM) [361][362][363][364][365][366], spinpolarized STM [366][367][368][369][370][371], scanning Kerr microscopy [372], scanning electron microscopy with polarization analysis (SEMPA) [373][374][375][376], photoemission electron microscopy (PEEM) [123,[377][378][379][380][381][382][383], Lorentz microscopy [384][385][386], electron holography [387,388], scanning Hall probe microscopy [389][390][391][392]. The imaging of the surface structure has contributed enormously to our understanding of the correlation between surface morphology and magnetism, in particular for mono...…”

The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy

“…There are a number of magnetic characterization techniques [18], and some give sufficient sensitivity for the magnetic characterization of an assembly of nano structures by collecting integrated data over a larger surface area. Examples are secondary electron microscopy with polarization analysis (SEMPA) [19][20][21], spin polarized low energy electron microscopy (SPLEEM) [22,23], magnetooptical Kerr-Effect (MOKE) [24,25], and x-ray magnetic circular dichroism (XMCD) [26][27][28]. However, these techniques cannot image and identify single nano structures on the low nm scale.…”

Development of a scanning electron microscopy with polarization analysis system for magnetic imaging with ns time resolution and phase-sensitive detection

“…The electrons of the (2,0)-beams are then counted by two perpendicularly arranged channeltron electron-counter pairs. The calculated asymmetry is proportional to the polarization of the electron beam and thereby quantitatively related to the surface magnetization of the investigated sample 19 . Using this detector geometry, the two in-plane spin polarization components can be measured at the same time by calculating the asymmetries of the counts:…”