Magnetic imaging with spin-polarized low-energy electron microscopy

Rougemaille, Nicolas; Schmid, Andreas K.

doi:10.1051/epjap/2010048

Cited by 116 publications

(94 citation statements)

References 125 publications

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“…We focus on Fe/Ni bilayer grown on W(110) substrates, where the very large spin Hall angle of tungsten 23 is combined with two-fold symmetry at the (110) interface and perpendicular magnetic anisotropy of the magnetic layer [24][25][26] . Using spin-polarized low-energy electron microscopy (SPLEEM) [27][28][29] , we observe anisotropic chiral DW spin structures with mixed components of chiral Bloch-and chiral Néel-character. We find that, as a function of the relative orientation of the DWs with respect to the [001] substrate surface direction, the Fe/Ni/W(110) system features chiral Néel walls, mixed chiral walls containing both Néel and Bloch components or non-chiral Bloch walls.…”

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Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain

et al. 2015

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Chiral magnetic domain walls are of great interest because lifting the energetic degeneracy of left-and right-handed spin textures in magnetic domain walls enables fast current-driven domain wall propagation. Although two types of magnetic domain walls are known to exist in magnetic thin films, Bloch-and Néel-walls, up to now the stabilization of homochirality was restricted to Néel-type domain walls. Since the driving mechanism of thin-film magnetic chirality, the interfacial Dzyaloshinskii-Moriya interaction, is thought to vanish in Bloch-type walls, homochiral Bloch walls have remained elusive. Here we use real-space imaging of the spin texture in iron/nickel bilayers on tungsten to show that chiral domain walls of mixed Bloch-type and Néel-type can indeed be stabilized by adding uniaxial strain in the presence of interfacial Dzyaloshinskii-Moriya interaction. Our findings introduce Bloch-type chirality as a new spin texture, which may open up new opportunities to design spin-orbitronics devices.

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Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain

et al. 2015

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“…), sensitivity. The most common magnetic microscopies offering spatial resolution below 50 nm and direct sensitivity to magnetization are X-ray Magnetic Circular Dichroism PhotoEmission Electron Microscopy (XMCD-PEEM) [ [7][8][9].Yet another criterion is the volume of the sample probed. This criterium is gaining in importance in the context of the emergence of three-dimensional (3D) magnetic objects and textures.…”

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“…), sensitivity. The most common magnetic microscopies offering spatial resolution below 50 nm and direct sensitivity to magnetization are X-ray Magnetic Circular Dichroism PhotoEmission Electron Microscopy (XMCD-PEEM) [1] and (Scanning) Transmission X-ray Microscopy [(S)TXM] [2], electron holography or Lorentz microscopy [3][4][5], Scanning Electron Microscopy with Polarization Analysis (SEMPA) [6], Spin-Polarized Low-Energy Electron Microscopy (SPLEEM) [7][8][9].…”

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Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

et al. 2015

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Shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy (XMCD-PEEM) is a recent technique, in which the photon intensity in the shadow of an object lying on a surface, may be used to gather information about the three-dimensional magnetization texture inside the object. Our purpose here is to lay the basis of a quantitative analysis of this technique. We first discuss the principle and implementation of a method to simulate the contrast expected from an arbitrary micromagnetic state. Text book examples and successful comparison with experiments are then given. Instrumental settings are finally discussed, having an impact on the contrast and spatial resolution : photon energy, microscope extraction voltage and plane of focus, microscope background level, electric-field related distortion of three-dimensional objects, Fresnel diffraction or photon scattering.Progress is continuous in the decreasing size and increasing complexity of nanosized magnetic systems being designed for either fundamental science or devices. Magnetic microscopies are crucial tools to monitor and understand the properties of such systems. Various types of information are desirable to gather, leading to multiple criteria to classify microscopies: spatial and time resolution, compatibility with environmental parameters such as variable temperature and applied magnetic field, requirements on the sample preparation and compatibility for ex-situ processing such as lithography, correlation with structural information, elemental sensitivity, quantity measured (magnetization, induction, stray field etc.), sensitivity. The most common magnetic microscopies offering spatial resolution below 50 nm and direct sensitivity to magnetization are X-ray Magnetic Circular Dichroism PhotoEmission Electron Microscopy (XMCD-PEEM) [ [7][8][9].Yet another criterion is the volume of the sample probed. This criterium is gaining in importance in the context of the emergence of three-dimensional (3D) magnetic objects and textures. The distribution of magnetization may be truly 3D if along the three directions in space the size of a system lies above magnetic characteristic length scales, such as the dipolar exchange length ∆ d for soft magnetic materials, or the anisotropy exchange length ∆ u for a hard magnetic material [10]. While this is obviously fulfilled in macroscopic materials, the complexity of magnetic textures is such that it cannot be measured in detail, and besides it cannot be controlled to achieve specific functions. The progress in nanofabrication techniques now allows to design suitable systems, both with top-down and bottom-up approaches. Let us give some examples. Flat magnetic elements are basic building blocks in spintronics, being patterned with great 2D versatility with thin film and lithography technologies. Large lateral dimensions may give rise to 2D magnetic textures, such as the so-called vortex state in disks [11]. Such textures are being investigated to design RF oscillator components, relying on the gyrotropic motion ...

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“…In addition, the high mobility of electrons (> 3x10 6 cm 2 V −1 s −1 ) and their long spin transportation distance (> hundred µm) are suitable properties for spatial imaging of this effect [5,[20][21][22][23]. The electron de Broglie wavelength at the Fermi energy is unusually long, around 20-100 nm [22], making it easy to design a suitable magnetic domain period a and minimize effects caused by nonzero domain wall width [18,19]. Further concern includes suitable materials for the grating formed by magnetic stripe domains.…”

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Proposal for electron quantum spin Talbot effect

2012

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We propose a quantum spin Talbot effect for an electron beam transmitted through a grating of magnetic nanostructures. Tunable periodic magnetic nanostructures can be used in conjunction with electron-beam illumination to create a spin polarized replica of the transversely periodic exit surface beam a Talbot length away, due to quantum interference. Experiments have been proposed to verify the effect in a two dimensional electron gas. This effect provides a new route to modulate electron spin distributions without a magnetic field. A quantum spin Talbot interferometer and transistor are proposed for spintronics applications.The ability to tune scalable semiconductor-based spintronics devices, based on the intrinsic spin of electrons to store and manipulate information, is both important and highly challenging for spin-based electronics since spin injection, spin accumulation and spin modulation of electrons are required [1][2][3][4][5]. Currently, manipulation of the spin during transport between injector and detector via spin precession and spin pumping can be accomplished [6], however, those methods have difficulty controlling spin distributions. By contrast, local tunability of spin distributions over nanometer scales is crucial for future solid state quantum computers based on electron spin [7]. Inspired by the progress in fabricating and controlling nanoscale magnetic structures [8], we propose a spin-dependent quantum Talbot effect for electron waves transmitted by a grating composed of magnetic nanostructures, to modulate the spin lattice pattern formed from a spin polarized replica of the structure upon propagation through a Talbot length period and adjustable by controlling the electron wavelength and magnetic nanostructures' period. This leads to potential applications such as a quantum spin Talbot transistor and a quantum spin Talbot interferometer.The optical Talbot effect was discovered in 1836 [9], and later explained by Rayleigh as a natural consequence of Fresnel diffraction. He showed that the Talbot length Z T is given by Z T = 2a 2 λ [10], in the paraxial approximation a ≫ λ, where a is period of the grating and λ is the wavelength of the incident light. However, in a nonparaxial regime where λ a<2λ, the Talbot effect is also operative for nonevanescent components of the scattered beam [11]. This effect reveals the wave-nature of both radiation and matter wave fields, examples of the latter including atoms, electrons and plasmons [11-13, 15, 16, 31].In this Letter, we calculate a spin polarized nonparaxial Talbot effect for electron matter waves transmitted through a grating composed of magnetic nanostructures. We find that the spin asymmetry of the transmitted field varies with distance from the grating, creating an electron spin replica of the structure a Talbot length away, in a non-paraxial regime where λ a<2λ. This creates a tunable spin lattice in two-dimensional space, which is a powerful method to manipulate elec- tron spin distributions in solid state systems. We find that the quantum...

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Magnetic imaging with spin-polarized low-energy electron microscopy

Cited by 116 publications

References 125 publications

Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain

Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain

Quantitative analysis of shadow x-ray magnetic circular dichroism photoemission electron microscopy

Proposal for electron quantum spin Talbot effect

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