New Magnetic Linear Dichroism in Total Photoelectron Yield for Magnetic Domain Imaging

Abstract

We report a dependence of the photoabsorption cross section as measured by total electron yield at the Fe and Co 3p thresholds on the sign of the magnetization for p-polarized light at oblique incidence.Peak-to-peak asymmetries up to 4% are observed. The asymmetry increases towards grazing incidence, where the total sample current is smallest.The transverse magneto-optic Kerr effect measured simultaneously shows a peak-to-peak asymmetry of up to 23% at the Co 3p threshold. The dichroism is used to image magnetic domains on an Fe (100) surface in a photoelectron emission microscope. PACS numbers: 78.20.Ls, 75.60.Ch, 78.70.Dm Spectroscopy of the core levels of the ferromagnetic transition elements has shown in recent years to be surprisingly rich in features caused by the Coulomb and exchange interactions between the core hole and the spinpolarized valence electrons. X-ray absorption experiments (XAS) with linearly polarized light [1] show a change of the spectra when the polarization vector is either parallel or perpendicular to the magnetization axis, according to the selection rules Am = 0 or Am =~1 , respectively. Magnetic circular dichroism (MCD) in x-ray absorption [2,3]can be understood as a spin-dependent excitation of core electrons into empty states above the Fermi level, whichbecause of the ferromagnetism are spin polarized [4].The spin dependence in the excitation arises from coupling between light helicity and the orbital momentum of the excited electron, which is in turn coupled to the spin of the photoexcited electron by spin-orbit interaction. Sum rules, which allow one to extract quantitatively spin and orbital moments, make MCD in absorption a very attractive technique [5]. By measuring the photoabsorption cross section via the total photoelectron yield of the sample, it is even possible to obtain spatially resolved and chemically specific magnetic information [6].In photoemission, even though the final state of the photoelectron far above the Fermi level has only negligible exchange and spin-orbit interactions, related effects can also be observed. It is well known that core level photoelectrons from ferromagnets in general carry a spin polarization due to exchange [7]. Apart from magnetic circular and "conventional" (as described above for XAS) linear dichroisrn, a new type of magnetic linear dichroism was recently reported for photoemission appearing on magnetization reversal [8]. This effect requires that the vectors of magnetization, electric radiation field, and electron emission form a chiral system with the angle between light polarization and electron emission different from 90, and occurs only in angle-resolved experiments. In photoabsorption, the angular acceptance of the excited electrons is not restricted, so that it is, in principle, an angle-integrating experiment. However, Kao and co-workers [9] reported in 1990 for photon energies near the Fe 2p excitation thresholds a change of the refIectivity for obliquely incident p-polarized light when the magnetization is switched between th...

Prediction of huge x-ray Faraday rotation at the GdN4,5threshold

“…The experimental demonstration of large changes in the specularly reflected X-ray intensity at the Fe L 2,3 edge 5 upon magnetization reversal initiated the ongoing search for magneto-optical (MO) effects in the soft X-ray regime, 6,7,8,9,10,11,12 as well as their application to element-specific studies of heteromagnetic systems. 13,14,15,16,17,18 Yet, in analyzing soft X-ray MO signals from thin films and multilayer systems with thicknesses comparable to the X-ray wavelength, previous investigations have shown 5,13,18 that a comparison with model calculations 19 of the reflected specular intensity (based on the Fresnel equations) is needed in order to extract a layerresolved sample magnetization profile.…”

Observation of Micro-Magnetic Structures by Synchrotron Radiation Photoelectron Emission Microscopy

“…It is reported that the signal is enhanced when the incidence angle of the light is going to the grazing condition. By using this new type of magnetic linear dichroism, the imaging of magnetic domains of the Fe(100) surface was demonstrated 24,41) as shown in Fig. 5(c).…”

Resonant magnetic reflectivity in the extreme ultraviolet spectral range: Interlayer-coupled Co/Si/Ni/Fe multilayer system

“…This feature can be clearly attributed to the resonant excitation of the Co at the M absorption edge and it is consistent with earlier findings. 10 A totally different behavior of the asymmetry A͑ , h͒ can be observed at the M absorption edge of Ni. At the lowest Si interlayer thickness ͑top graph͒, the magnetic asymmetry has only a dip shape with a negative extremum of about −25% at an energy of 66.75 eV and an angle of 47°.…”

“…Several experiments have already shown that magnetic investigations of single films by resonantly scattered XUV light at the M absorption edges of transition metals [10][11][12][13][14] and the N absorption edges of the lanthanide series 20,21 yield very strong magnetodichroic signals. Moreover, studies of the Faraday rotation and the Voigt effect at the M and L absorption edges of Fe, Co, and Ni reveal that magneto-optical constants and thus responses at the M edges are as large as those at the L edges.…”

“…In terms of the magnetooptical response, these XUV phenomena have been found equally useful, with changes in the dichroic contrast ranging up to almost 100%. [10][11][12][13][14] Because the majority of beamlines at third-generation synchrotron facilities are dedicated to photon energies in the soft x-ray region, the opportunity of XUV magneto-optical studies has mostly escaped the attention of the magnetic community. However, recently substantial progress has been made in laser-based light sources reaching photon energies of up to 100 eV with moderate effort justifying a closer look into XUV magneto-optics.…”