Photoemission of CO/CU(100). Non-Relativistic Spin- and Angle-Resolved Normal Emission
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PHOTOEMISSION OF CO/CU(100). NON-RELATIVISTIC SPIN- AND ANGLE-RESOLVED NORMAL EMISSION. R. Schneeweiss, U. Konig, J. Redinger and P. Weinberger Institute for Technical Elektrochemistry, Technical University Vienna, C. M. Schneider and J. Kirschner FB Physik, Free University Berlin
ABSTRACT The Co/Cu(100) system is the first system known where the contributions to the spin polarisation of spin-orbit coupling and the ferromagnetic overlayer were clearly distinguished experimentally. In order to get a first understanding of the photoemission data non-relativistic spin-polarized photoemission calculations are performed for one and two overlayers of Co on Cu(100).
INTRODUCTION As can be seen from Fig. 1 the Co/Cu(100) system shows thickness dependent magnetic behaviour which results into a large reduction of the critical temperature for thin Co coverages [1]. Furthermore Co films exhibit a considerable big magnetic anisotropy, which gives rise to an orientation dependency of spin-polarized photo-emission spectra with respect to the magnetisation in the surface. Band structure calculations reveal that the magnetic moment of the Co monolayer is 1.8t-B [21, i.e. is 15% bigger than the corresponding bulk value (1.56JUB [3], 1.6 5/•B [4]). This enhancement, however, is considerably smaller than for instance in Fe/Cu(100) (2.851AB for the Fe monolayer vs. 2 .12 tiB in bulk
Fe [51).
COMPUTATIONAL DETAILS We used a one-step-model for the calculation of the photoemission spectra of a Co monolayer on a Cu substrate. Table I displays all computational details. Since the FLAPW calculations do not provide information concerning the lifetimes for the final and the initial (hole) states we followed the results of McRae [6]. The theoretical spectra are convoluted with a Gaussian spectrometer function of 0.2 eV full width at half maximum and are individually normalized to the highest peak. Taking into account that the local density approximation (LDA) usually leads to a rigid shift of at least 0.3 eV towards higher binding energies, the present photocurrent calculations with the listed values for Mat. Res. Soc. Symp. Proc. Vol. 253. 01992 Materials Research Society
500
T=305K 22 ML tee-Co fC-.Co onCu(100)
1400
T=305K
T--
T=275K
_ -
1200
T=245K
10001 T--155K
a CD -20 CD
800 F
-10 0 10 magnetic field (0e)
20
CL E 600F 0_)
400F
200101L 0
coating with Cu
-t
1
2
3
4
cobalt coverage in monoloyers
5 [ML]
Fig. 1: Thickness dependence of the Curie temperature of fcc-Co films. Inset: Hysteresis loops from a 2ML film as a function of sample temperature. TABLE I.: Computational parameters
potential: Co/Cu(100)
2Co/Cu(100) vacuum region highest I value beams layer doubling: initial state final state photon energy range absorptive potential: initial state final state
muffin-tinized FLAPW 7 layer slab [2] muffin-tinized FLAPW 9 layer slab [8] z-dependent [9]
4 21 128 layers 16 layers 11 to 21 eV 0.135 eV 0.54 to 1.63 eV with increasing photon energy
501
2Co-Cu(1 00) Normal emission
e,= 0o,s-pol maj./min. hv(eV) C
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