Magnetic dichroism has been observed in the angular distribution of p-core level photoemission spectra excited from crystalline ferromagnets by unpolarized X-rays. The angular dependence of the angular and energy-resolved photoemission intensity was recorded as a function of the emission direction with respect to the crystal, revealing a strong variation of the magnetic dichroism with emission angle due to photoelectron diffraction. This variation is particularly strong around the forward scattering peaks, including sign reversals close to these directions. The results demonstrate that any standard X-ray photoelectron spectroscopy apparatus possesses the potential for combined analysis of surface magnetic structure and geometric structure in a chemically specific way.

For two x-ray incidence directions onto an epitaxial FeNi(001) film, one to the left and a second one to the right side of the symmetry plane spanned by the magnetization direction and the photoelectron wave vector, we have measured distributions of the emission-angle dependence with respect to the crystallographic axes of the Fe ${2p}_{3/2}$ core-level photoelectron intensity asymmetry occurring upon magnetization reversal. The two angular distributions transform into each other when the signs of the magnetization and of the photoelectron emission angle are inverted, in accordance with the conservation of parity.

By core level x-ray photoelectron spectroscopy using an x-ray tube, ultrathin films of FexNi1-x alloys deposited epitaxially on a Cu(001) substrate have been investigated. Structural information is obtained by means of core level photoelectron diffraction. The angular dependent intensity scans reveal peaks corresponding to a face-centered-cubic lattice in the covered concentration range 0.08<x<0.9. Information on the local magnetic moments is obtained by observing the intensity asymmetry occurring when switching between directions of opposite magnetization (MLDAD) Both the Fe 2p(3/2) and Ni 2p(3/2) asymmetries show a maximum at about 50% Fe concentration. (C) 1999 American Institute of Physics. [S0021-8979(99)72908-7].

We discuss the relation between a photoelectron diffraction (PED) related core-level magnetic-field-induced intensity asymmetry ("magnetic dichroism") and the dependence of the structure and the local magnetic moments on Fe100-xCox/Ag(001) epitaxial ultrathin alloy films. Data ale obtained using a standard laboratory x-ray source. The 2p core levels of Fe and Co at any of the alloy compositions show FED patterns indicative of bcc environments of the emitter atoms. The magnetic dichroism of the Fe 2p(3/2) core level increases with increasing x, whereas it is virtually constant for the Co 2p(3/2) level. Roth dependencies scale well with the calculated variation of the local magnetic moment with alloy composition. [S0163-1829(98)04725-0].

The structure and element-specific local magnetic moments in Fe100-xCox/Ag(001) (16<x<70) epitaxial ultrathin alloy films have been determined by photoelectron diffraction (PED) and related magnetic linear dichroism in angle-resolved core-level photoemission, using a laboratory x-ray source. The FED peaks of the Fe and Co 2p core levels for any of the alloy compositions are at emissisn angles as expected for a bcc lattice. The dichroism increases for the Fe 2p(3/2) core level with increasing x, whereas that of the Co 2p(3/2) dichroism is virtually independent on the alloy composition. The dichroism of both the Fe and the Co core levels scales well with the calculated dependence of the local magnetic moment on the alloy composition rather than with the average saturation magnetization. (C) 1998 American Institute of Physics. [S0021-8979(98)40311-6].

Magnetic dichroism has been measured in angle-resolved core-level photoemission from the Fe 2p and 3p levels in epitaxially grown ultrathin films of Fe(001) and in an amorphous metallic glass with composition Fe78B13Si9. Unpolarized Al K alpha and Mg K alpha radiation was used for excitation, leading to diffraction patterns that are dominated by forward scattering along low-index crystallographic directions. The Fe(001) data for both total intensity and magnetic dichroism are quantitatively compared to theoretical calculations at both a two-atom single-scattering level and a multiatom multiple-scattering level. Strong effects on the magnetic dichroism due to photoelectron diffraction are found, and the combined angle and energy dependence of the dichroism shows a characteristic "checkered" pattern that should be generally observable in all single crystals. Comparing dichroism data obtained for single-crystal Fe films with those obtained from the amorphous glass and from two-atom and multiatom diffraction theory further permits estimating the relative contributions of free-atom-like dichroism and of photoelectron diffraction, with the free-atom dichroism (that is dominant along low-index directions) being smaller by about a factor of 2 to 4 than the maximum diffraction dichroism (that dominates away from low-index directions). Such photoelectron-diffraction-produced magnetic dichroism thus should provide a useful tool for studying magnetic order near single-crystal surfaces. The deviation of the zero in the dichroic asymmetry from the low-index directions is also found via photoelectron diffraction theory to be very sensitive to the s-to-d partial-wave phase difference, and the experimental data permit estimating this quantity and the solid-state effects on it.

Magnetic dichroism has been observed in the angular distributions of Fe 2p photoemission spectra excited from Fe(001) by unpolarized 1.25-keV x rays. The dichroism varies strongly around each low-index forward-scattering direction in the crystal, exhibiting an antisymmetry with emission direction and binding energy that is centred on each forward scattering peak. Photoelectron diffraction theory provides a quantitative explanation for these unpolarized dichroism effects, which should also be generally useful in surface magnetism studies.

We have investigated the angular dependence of the magnetic linear dichroism occurring in angle-resolved photoemission (MLDAD) from epitaxial Co films on Cu(001) using unpolarised HeI- and MgKα-radiation. Spectra were taken while rotating the sample about the magnetisation direction for fixed angle between the directions of light incidence and photoelectron collection. We observe a strong dependence of the MLDAD asymmetry on the electron emission direction with respect to the surface normal showing the importance of photoelectron diffraction in MLDAD.