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

Abstract

Scanning electron microscopy with polarization analysis is a powerful lab-based magnetic imaging technique offering simultaneous imaging of multiple magnetization components and a very high spatial resolution. However, one drawback of the technique is the long required acquisition time resulting from the low inherent efficiency of spin detection, which has limited the applicability of the technique to certain quasi-static measurement schemes and materials with high magnetic contrast. Here we demonstrate the ability to improve the signal-to-noise ratio for particular classes of measurements involving periodic excitation of the magnetic structure via the implementation of a digital phase-sensitive detection scheme facilitated by the integration of a time-to-digital converter to the system. The modified setup provides dynamic imaging capabilities using selected time windows and finally full time-resolved imaging with a demonstrated time resolution of better than 2 ns.

Direct Imaging of Chiral Domain Walls and Néel‐Type Skyrmionium in Ferrimagnetic Alloys

“…In this study, we investigate the chirality of spin textures in a ferrimagnet namely Ta/Ir/Fe/GdFeCo/Pt by imaging the spin structure of the domain walls using SEMPA [25][26][27]. This surface-sensitive imaging technique has already been successfully used to determine the chiral character of out-of-plane (OOP) magnetized spin textures in ferromagnetic materials [28][29] and here we demonstrate that we can determine the chiral character of spin textures also for ferrimagnetic materials.…”

New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

“…[18] Copyright 2017, American Physical Society. methods, for example, MFM, that provide a spatial resolution up to 50 nm for curved nanoobjects; [9,101,169,245,247,[303][304][305][306][307] MOKE microscopy, [27,144,235,248,294] that recently was enabled for pump-probe time-resolved measurements of micro-tetrapod geometries; [284] electron-based methods, including Lorentz transmission electron microscopy (TEM) [308,309] and off-axis electron holography, [310,311] that allows to perform the detail static reconstruction of magnetic textures in flat [312,313] and 3D [240,287,314] curved geometries, see Figure 8g; scanning electron technique with polarization analysis (SEMPA), [315] that is suitable for imaging flat curved magnetic geometries, [288,316] see Figure 8h; X-ray-based visualization methods, including X-ray magnetic circular dichroism photoelectron emission microscopy (XMCD-PEEM). [9,24,25,317,318] While these methods are limited to the analysis of simple magnetic geometries, the visualization of complex 3D shape geometries requires the utilization of the tomographic-based approaches.…”

“…For instance, recently it was shown experimentally the possibility to perform dynamic magnetic imaging of flat curved geometries by means of scanning electron microscope with polarization analysis (SEM-PA), [288] that has a time resolution of less than 2 ns. [315] (iii) Transport Methods: In touch with the prospective development of spintronics and spin-orbitronics in flat magnetic systems, it is necessary to extend the transport-based methods on curved magnetic architectures. Thus, the possibility to measure the field-like and damping-like spin-orbit torques from the first and second harmonics of Hall signal [372] provides a quantitative assessment for the intrinsic DMI constant, [373] which could be adapted to the curvilinear magnetic systems and extrinsic or mesoscale DMI assessment.…”

Ultrafast electron microscopy for probing magnetic dynamics

“…Magnetic image contrast using electrons arises through both inelastic and elastic scattering. With low incident electron energy, scanning electron microscopy with polarization analysis (SEMPA) [66][67][68][69][70][71] probes the local surface magnetization by sampling the spin polarization of emitted secondary electrons, and spin-polarized low-energy electron microscopy (SPLEEM) offers magnetic contrast in reflection, 72,73 because the inelastic and elastic electron mean free paths depend on the relative orientation of electron spin and local surface magnetization. Higher incident-energy electrons can excite atomic transitions sensitive to material electron spin polarization, analogous to XMCD; this technique, called electron magnetic chiral dichroism (EMCD), employs crystalline diffraction to select outgoing electron orbital angular momentum states corresponding to different transitions.…”