Simon A. Morton

Spin-resolved photoelectron spectroscopy of Fe3O4 ☆

Abstract Spin-polarized photoelectron spectroscopy has been used to study the candidate half metal Fe 3 O 4 . By using higher photon energies we can study polarization in “as received” samples, essentially “looking through” the disrupted surface. Our data agree with theoretical calculations for Fe 3 O 4 but exhibit a lowered polarization.

Evidence of dynamical spin shielding in Ce from spin-resolved photoelectron spectroscopy

Using Fano effect measurements upon polycrystalline Ce, we have observed a phase reversal between the spectral structure at the Fermi edge and the other 4f derived feature near a binding energy of 2 eV. The Fano effect is the observation of spin polarized photoelectron emission from nonmagnetic materials, under chirally selective excitation, such as circularly polarized photons. The observation of phase reversal between the two peaks is a direct experimental proof of Kondo shielding in Ce, confirming the predictions of Gunnarsson and Shoenhammer, albeit with a small modification.

Facilities for the Performance of Fano Effect Measurements as a Probe of Electron Correlation

Fano Effect measurements are the key to direct observation of the Kondo or spin shielding intrinsic to models of electron correlation. The Fano Effect is the observation of spin polarized photoelectron emission from NONMAGNETIC materials, under chirally selective excitation, such as circularly polarized photons. Below are described three spectrometers, with which Fano Effects measurements have been made. The key measurements are based upon spin-resolving and photon-dichroic photoelectron spectroscopy. True spin-resolution is achieved by the use of a Mini-Mott detection scheme. The photon-dichroic measurements include the variants x-ray magnetic circular and linear dichroism angular distributions (XMCDAD and XMLDAD). Both a multichannel, energy dispersive collection scheme as well as the spin-detecting Mini-Mott apparatus are used in data collection.

X-ray Magnetic Linear Dichroism of Fe-Ni Alloys on Cu(111)

Abstract : We have prepared Fe(x)Ni(1-x) multilayers on Cu(111) in order to learn how to control the structure and magnetism of these thin alloy films, which are relevant to the giant magnetoresistance (GMR) effect used in magnetic disk drive beads. Using the Spectromicroscopy Facility (7.0.1.2) on Undulator Beamline 7.0 at the Advanced Light Source, we have measured X-ray magnetic linear dichroism (XMLD) signals from both Fe and Ni 3p lines for fourteen different thin Ni-Fe alloy films on Cu(111), with Fe concentration ranging from 9% to 84% and for a variety of film thicknesses. The Curie temperature for all of these samples was in the range 200 K to 500 K. For many of these films, the Curie temperature was considerably lower than was previously seen for similar films deposited on Cu(100). For a particular Fe concentration x, the Curie temperature increases with alloy film thickness. For a specific film thickness, the Curie temperature has a maximum near x approx. 0.4.

The Utilization of Spin Polarized Photoelectron Spectroscopy as a Probe of Electron Correlation with an Ultimate Goal of Pu

Spring 2008 Materials Research Society Meeting Actinides IV, Symposium NN San Francisco, CA, USA March 24-28, 2008 The Utilization of Spin Polarized Photoelectron Spectroscopy as a Probe of Electron Correlation with an Ultimate Goal of Pu J.G. Tobin 1 , S.W. Yu 1 , B.W. Chung 1 , S.A. Morton 1,2 , T. Komesu 3 ,* and G.D. Waddill 3 1.Lawrence Livermore National Laboratory, LLNS-LLC, Livermore, CA, USA 2.Lawrence Berkeley National Laboratory, Berkeley, CA, USA 3.University of Missouri-Rolla, Department of Physics, Rolla, MO, USA We are developing the technique of spin-polarized photoelectron spectroscopy as a probe of electron correlation with the ultimate goal of resolving the Pu electronic structure controversy. Over the last several years, we have demonstrated the utility of spin polarized photoelectron spectroscopy for determining the fine details of the electronic structure in complex systems such as those shown below. The proposed half-metallic ferro-magnet Fe3O4 [Figure 1, Ref 2] Figure 1 a) Spin resolved photoemission spectra from a) “as received” sample hν=160eV. b) Spin resolved photoemission spectra from a sample after Ne+ sputtering, hν=160eV. Note the large effect observed in the as received sample in (a) and the reduction of the effect in (b) Tobin Page 1