Browsing by Author "Timmermans, Eddy M. E."

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    Magnetic electron emission holography
    (1993) Timmermans, Eddy M. E.; Trammell, George T.
    I show that the difference in 'spin up' and 'spin down' angular intensities of electrons emitted from inner core levels of atoms in a magnetic crystal is a spin hologram. Its inverse 'pictures' the component of the spins in the neighborhood of the emitter in the direction that the detected electrons are spin analyzed. Measuring the spin difference in three orthogonal directions determines a vector hologram which gives an image of the atomic spin vectors. I develop the theory and illustrate the feasibility and potential of this novel technique by means of model calculations. Furthermore, I give a detailed treatment of the elastic scattering processes that are responsible for the spin holograms, and study the effect of multiple scattering and self-interference which could cause complications.
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    Spin holography
    (1995) Timmermans, Eddy M. E.
    In electron emission holography, the sources are electron emitting atoms. The primary (unscattered) electron wave interferes with the waves scattered elastically by nearby atoms resulting in a holographic fringe pattern in the angular distribution of the emitted electrons. In cases that the neighboring atoms have non-zero spins the scattered electron wave depends on the spin of the scattering atom by virtue of exchange scattering and the holographic fringes are spin dependent. This is the basis of the holographic spin imaging technique that we propose and discuss in this thesis, and which, we believe, will become a very powerful method for determining the short range spin environment of the electron source atoms in surface magnetism studies. We show that the "vector hologram" obtained by measuring the spin of the emitted electrons, S(scR), can be inverted to give a three-dimensional image of the magnetic environment of the electron emitting source atom. Of greater practical and theoretical interest, we show that the same information can be obtained from photoelectron intensity patterns, I(scR), ("scalar" spin holography) produced with incident linearly polarized photons. This surprising result is very important since it brings spin holography well within the realms of present day experimental capabilities available at synchrotron sources. In addition, we develop the theory for the related spin dependent EXAFS experiments, and show that the SPEXAFS data can be analyzed to yield much more information than previously realized. In particular, the SPEXAFS technique can be used for the study of antiferromagnetic spin arrangements, as well as ferromagnetic ones.