Spin-Resolved Photoemission (original) (raw)
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Electron Spin Polarization: A New Tool in Photoemission and Magnetism
Resume. -On passe en revue la technique permettant de mesurer la polarisation du spin P des electrons emis par effet photoelectrique et on presente des rksultats obtenus pour differents materiaux magnetiques. Les courbes de magnetisation photoelectrique s'obtiennent en mesurant P en fonction d u champ magnCtique applique tandis que la nlesure de P en fonction de I'energie des photons livre un spectre de la polarisation du spin qui permet de localiser les Ctats magnetiques dans un schCma des niveaux d'energie. Les valeurs positives de P observees pour Ni et Co sont en desaccord avec les predictions s'appuyant sur le n~odele de bande du ferromagnetisme. Dans les semiconducteurs desordonnes apparaissent dans la zone interdite de nouveaux ttats qui sont occupes par un seul electron et qui renforcent le coupiage ferromagnetique des spins localisCs des ttats 4f. La presence d'une couche magnetique non saturee a Cte trouvee a la surface d'un monocristal ferromagnetique tel que EuO. Cette couche morte est a I'origine d'une diffraction d'echange du spin pour les electrons provenant de I'interieur ferromagnetique du cristal. Le dopage avec des ions metalliques trivalents a pour effet d'augmenter P, car les electrons supplb mentaires renforcent le champ molCculaire dans la couche superficielle paramagnetique.
CIRCULAR POLARIZATION OF PHOTONS FOR MAGNETIC MATERIALS STUDIES
Modern scattering theories had suggested in 1970 the possibility of the use of x-ray to study the magnetic density in the magnetic materials such as iron and cobalt. This proposal has encountered many difficulties when using traditional x-ray sources and the reason is that the intensity of photons from these sources is weak and that the magnetic property to be studied is weak as well. But with the progress in building Synchrotrons it was possible to obtain photons with high intensity and circular polarization properties that enabled the study of many magnetic materials. In this paper the polarization properties of Synchrotron radiation are presented. Also the famous Compton scattering equation is introduced and the magnetic Compton scattering equations are presented along with the introduction of methods for studying magnetic properties of materials using circular polarization of photons.
Spin-polarized photoemission spectroscopy of magnetic surfaces using undulator radiation
Review of Scientific Instruments, 1992
A beamline has been established at the National Synchrotron Light Source to perform angleresolved photoemission experiments on magnetic surfaces with spin sensitivity. The system has two novel features: it uses a miniature electron-spin polarization analyzer and it also uses synchrotron radiation from an undulator rather than a bending magnet.
Electron spin polarization analyzers for use with synchrotron radiation
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1988
The measurement of the spin polarization of photoelectrons emitted from a magnetic material is discussed. An important consideration is the acceptance phase space of the spin analyzer relative to the phase space of the photoemitted electrons to be measured. Other considerations include the magnetization direction relative to the extracted beam and whether the measurements are angle integrated or angle resolved. In the longitudinal geometry where the magnetization is normal to the sample surface and along the extracted photoelectron beam, conservation of canonical angular momentum adds an additional magnetic term to the beam emittance which is absent when the magnetization is in the sample plane and transverse to the extracted beam. For angle resolved measurements in the transverse geometry, the advantages of a new, low-energy (-100 eV) spin analyzer which is easily movable, compact and efficient are discussed. Different spin analyzers are described and compared, and an analysis of their application to different spin polarized photoemission measurement configurations is given.
Physical Review B
Magnetic dichroism in spin-and angle-resolved core-level photoemission is investigated within the relativistic one-step model of photoemission based on multiple-scattering theory. Photoelectron scattering in emission from 3p levels of low-index Fe and Ni surfaces is found to affect intensities, dichroism, and photoelectron spin polarizations considerably, in particular in off-normal emission. In general, the calculated spectra agree well with their experimental counterparts in spectral shape, size of the dichroic signal, and spin polarization. Magnetic circular dichroism in a chiral setup is analyzed theoretically using appropriately defined asymmetries. Further, core-level energy positions and photoemission are compared with those obtained within an atomic model. ͓S0163-1829͑99͒10621-0͔
A two-photon photoemission study of spin-dependent electron dynamics
Surface Science, 2006
We describe a spin-and femtosecond time-resolved two-photon photoemission experiment with an overall energy resolution of 90 meV and an angular resolution of ±2.5°at an electron count rate of a few kHz. As a model system we have studied image-potential states in front of a three monolayer iron film on Cu(1 0 0). With our setup an exchange splitting of both, the n = 1 and n = 2 image-potential state is clearly discernible. A strong dependence of the spin polarization in the image-potential states on the polarization of the pump light can be observed. Time-resolved measurements reveal that the lifetime of excited majority-spin electrons exceeds that of minorityspin electrons by a factor of 1.4.
Theory of spin polarized photoelectron diffraction
Journal of Magnetism and Magnetic Materials, 1991
We discuss several aspects of the theory of spin-polarized photoelectron diffraction (SPPD) This method make\ use of muldplet splittings of core-level bmchng energies to produce photoelectron peaks with high spm polallzatton (for example. rhe two principal peaks associated with Mn 3s emission from Mn'+ ). We consider three pos?tble mechanisms for spm-dependent photoelectron scattering and diffraction: exchange scalterrng by valence electrons (3dF for Mn?' ), sprn-orblt scattermg (whch IS not expected to yield large effects if the sample does not have a net magnetization). and spm-dependent melasrlc scattering (which cannot yet be dealt with in a fully quantitative way. but IS estimated lo be less important than the other tuo) The fact that SPPD involves internal sources of polarized electrons references to their respective emlllers Imph:s that It can he employed to study magnetic order in both anti-ferromagnets and ferromagnets and at temperatures above their re,pectlve NPel or Curie points. The effects of exchange scattering on Mn 3s emission from Mn'+ m KMnF, have been incorporated mto a single-scattering cluster model of the diffraction process via either the Dlrac-Hara or Kohn-Sham local den\lrh approvjmations Thus model IS applied lo several cases: z single Mn'* scatterer. small clusters of Mn' ' bcatlerers. and full clusters appropriate lo the (110) surface of KMnF,, with all atoms included. These calculallons demonstrate that SPPD should be L short-range probe of magnetic order, a result conslslent with conclusions reached m several prior sludlrs of photoelectron dtffractmn without spun resolution They also Illusrrate the perrurbatlve nature of these effects. which are onl! &out CA S-1555 of the total Intensity. this m turn leads lo several possible slmphflcatlons m the theon. We hate m addltlon phenomenologlcally modelled the decreases of short-range order with increasmg temperature by uhmg d GaussIan modul'itlon of spins: this model produces curves of SPPD spn asymmetry versus Gau\alan \vtdth which qudiltdfl\cIy ,lgree \\lth tho\r ohserved evperlmentally (Phys Rev Letl 55 (1986) 1227) Direct comparlhom of the ohsrned angul~ dependence of Ihr\c spin asymmetries with theory for (1 IO) KMnF, are also encouraging m that trend\ from onr directIon 10 another Jrc' 111 gencr,ll predlctcd correctly. tiowe\er, the ma\tmum degree of a5)rnmctr> predlctcc 1 hj thcl>r) (13%) I\ rome\\hat heIt,\\ th.lt of experiment (17%). Possible reasons for the discrepancies seen bet _n theory and experrment arc dIscusbed. together with likely future directlons of study. e!ect.ron crwrtmcmnim f2,_7!_ "r-"'-"-r-'~ of partiaiiy-fiiied 3d transition inct,ll at,,~tlt~ dtlU tOnS usually have large sphttings (roughly proportional to their respective magnetic moments ). thus making the 3s doublet the most convenient source of spin polarized photoelectrons for magnetic materials containing such species. In rareearth systems, the 4s or 5s levels should play an
Surface Science, 1995
We measured the CDAD from NO on Pt(111) at the SX/700-III monochromator at the synchrotron BESSY in Berlin. We found high asymmetries up to 60% using a photon energy of 40 eV. Surprisingly, this is higher than the degree of circular polarisation that should be between 30% and 50% for the experimental parameters used. This obvious contradiction can be explained if an additional dichroism arising from a strongly linear polarised component of the radiation at the SX/700-III source is taken into account. The polarisation of this component has the orientation of ±45° with respect to the synchrotron plane. This linear polarisation changes its sign if the circular polarisation is changed, too. First experiments on this linear dichroism show large asymmetries for CO/Pt(111), comparable to the CDAD asymmetries.
Magnetic dichroism in atomic core level photoemission
The European Physical Journal Special Topics, 2009
The overview covers selected topics on magnetic dichroism in atomic core level photoemission: the geometrical model in photoionization of laser polarized atoms and its generalization, contributions to the complete experiment from magnetic dichroism studies and nondipole effects in magnetic dichroism.