Scanning-Ion Microscopy with Polarization Analysis (SIMPA)
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SCANNING-ION MICROSCOPY WITH POLARIZATION ANALYSIS (SIMPA)
N. J. Zheng and C. Rau Department of Physics and Rice Quantum Institute, Rice University, Houston, TX 77251.
ABSTRACT
We have developed a novel, high-resolution magnetic imaging technique, scanning-ion microscopy with polarization analysis (SIMPA). In SIMPA, a highly-focused, scanning Ga÷ ion beam is used to excite spin-polarized electrons at surfaces of ferromagnetic materials. By measuring the intensity and the spin polarization of the emitted electrons using a newly developed, compact Mott polarimeter, topographic and magnetic images of magnetic structures are obtained. We report on first SIMPA studies on single-crystalline Fe samples.
INTRODUCTION
Quite recently, secondary electron emission (SEE) has attracted, particularly in combination with analysis of the electron spin polarization (ESP), broad scientific attention. This has been shown by the implementation of secondary electron microscopy with polarization analysis (SEMPA) [1] and of spin-polarized electron emission spectroscopy (SPEES) [2]. Electronand ion-induced SEE provides a high electron yield which is needed for efficient, highresolution topographic and spectroscopic imaging of surfaces. Besides this, there are two addition features that show the great scientific and technological potential of the use of SEE for the topographic and magnetic imaging of surfaces. Firstly, the ESP of low-energy electrons (< 10 eV) emitted from ferromagnetic surfaces materials is enhanced by a factor of two or three as compared to the average magnetization of the material (valence band polarization) [3]. This, when utilized for magnetic imaging, will enhance the image contrast by a factor of four to six. Secondly, the inelastic mean free path of these low-energy electrons in 3d transition metals is, as recently found [4], only of the order of one or two monolayers, which is much shorter than the values published (3 nm - 5 nm) in the past decades. It is especially this characteristic that makes the use of SEE very attractive for high-resolution, topographic and magnetic imaging of bulk and ultrathin film materials. With growing interest in magnetism in thin film and multilayer-structured systems, especially with respect to their potential technological applications, a deeper and more fundamental understanding of the influence of the geometrical and chemical micro-structure on surface and interface magnetic properties becomes an area of revived scientific research. In this paper, we report on a novel, high-resolution magnetic imaging technique, scanningion microscopy with polarization analysis (SIMPA). In SIMPA, a micro-focussed ion beam is used to excite electrons at the surface and in deeper-lying layers of a magnetic material. As shown in several recent publications, these ion-induced electrons are spin-polarized [2, 5, 6]. An enhancement of the ESP of the emitted low-energy electrons is found similar to that detected in electron-induced SEE from magnetic materials. In addition, it is found that the surfac
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