research papers 864 https://doi.org/10.1107/S1600577521002307 J. Synchrotron Rad. (2021). 28, 864–875 Received 7 November 2020 Accepted 28 February 2021 Edited by P. A. Pianetta, SLAC National Accelerator Laboratory, USA Keywords: spin detector; spin-filter effect; spin-resolved ARPES. A new imaging concept in spin polarimetry based on the spin-filter effect Oleg E. Tereshchenko, a,b * Vladimir A. Golyashov, a,b Vadim S. Rusetsky, a,c Andrey V. Mironov, c Alexander Yu. Demin c and Vladimir V. Aksenov c a Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090, Russian Federation, b Novosibirsk State University, Novosibirsk 630090, Russian Federation, and c CJSC EKRAN-FEP, Novosibirsk 630060, Russian Federation. *Correspondence e-mail: teresh@isp.nsc.ru The concept of an imaging-type 3D spin detector, based on the combination of spin-exchange interactions in the ferromagnetic (FM) film and spin selectivity of the electron–photon conversion effect in a semiconductor heterostructure, is proposed and demonstrated on a model system. This novel multichannel concept is based on the idea of direct transfer of a 2D spin-polarized electron distribution to image cathodoluminescence (CL). The detector is a hybrid structure consisting of a thin magnetic layer deposited on a semiconductor structure allowing measurement of the spatial and polarization-dependent CL intensity from injected spin-polarized free electrons. The idea is to use spin- dependent electron transmission through in-plane magnetized FM film for in- plane spin detection by measuring the CL intensity from recombined electrons transmitted in the semiconductor. For the incoming electrons with out-of-plane spin polarization, the intensity of circularly polarized CL light can be detected from recombined polarized electrons with holes in the semiconductor. In order to demonstrate the ability of the solid-state spin detector in the image-type mode operation, a spin detector prototype was developed, which consists of a compact proximity focused vacuum tube with a spin-polarized electron source [p-GaAs(Cs,O)], a negative electron affinity (NEA) photocathode and the target [semiconductor heterostructure with quantum wells also with NEA]. The injection of polarized low-energy electrons into the target by varying the kinetic energy in the range 0.5–3.0 eV and up to 1.3 keV was studied in image-type mode. The figure of merit as a function of electron kinetic energy and the target temperature is determined. The spin asymmetry of the CL intensity in a ferromagnetic/semiconductor (FM-SC) junction provides a compact optical method for measuring spin polarization of free-electron beams in image-type mode. The FM-SC detector has the potential for realizing multichannel 3D vectorial reconstruction of spin polarization in momentum microscope and angle-resolved photoelectron spectroscopy systems. 1. Introduction 1.1. Free-electron spin detection: from single- to multi- channel mode 1.1.1. Electron spin detection via spin–orbit interactions. Detection of electron spin with the efficiency of spin- integrated angular-resolved photoelectron spectroscopy (ARPES) is a major issue in modern photoelectron spectro- scopy, which initiated the search for an ‘ideal’ spin filter for free electrons. The definition of an ‘ideal’ spin detector can be formulated in terms of the capability of high-efficiency multichannel (image-type) spin detection simultaneously with normal ARPES or momentum microscopy measurements. Spin detectors developed to date are based on the phenomena caused by spin–orbit interactions (SOIs) of the electron or the ISSN 1600-5775 # 2021 International Union of Crystallography