Implementation of SEMPA using a high efficiency retarding-potential Mott polarimeter

Abstract

Scanning Electron Microscopy with Polarization Analysis (SEMPA) provides a novel tool with which to image surface magnetic structure. In SEMPA, a tightly focussed electron beam is directed at the sample surface and the polarization of the ejected low-energy secondary electrons, which mirrors the local surface magnetization, is measured. A magnetic image is then built up by scanning the incident electron beam point-by-point over the sample surface. Here, a new SEMPA instrument is described that makes use of a high-efficiency retarding-potential Mott polarimeter. The incident electron beam is provided by an ISI-SX40 SEM column. Low-energy secondary electrons ejected from the sample surface are collected and transported to the Mott polarimeter by a series of electrostatic lenses. A Wein spin rotator is also included in the electron transport optics to allow measurement of the full vector polarization of the ejected electrons, and thus the surface vector magnetization. Tests show that the performance of the present SEMPA instrument is superior to that of earlier designs. The apparatus has been used to image the domain structure on the surface of an Fe 3% Si sample, and to image tracks recorded in-plane on a cobalt alloy medium.