Speaker
Ali R. Koymen
(University of Texas at Arlington)
Description
The ability of positrons to create polarized core holes stems from the fact that the annihilation rate for spin singlet collisions is 1115 times faster than for spin triplet collisions and thus ~558 times faster with an electron of opposite spin. It is therefore possible to use the inherent polarization of positron beams to create polarized core holes with a net polarization approximately equal in amount and opposite in direction of the incident positron beam. This allows a method for the investigation of magnetism using spin-polarized positron beams due to the preferred annihilation of electrons and positrons when their spins are aligned anti-parallel. As a result of this, by applying an external magnetic field the positrons will annihilate predominantly with electrons from the majority (when magnetic field is parallel to the positron spin-polarization) or the minority (when magnetic field is anti-parallel to the positron spin-polarization) spin directions. At low positron beam energies (less than 20eV) this method can be used to study surface magnetism and also measure element specific magnetization using spin- polarized Positron Annihilation Auger Electron Spectroscopy. Using a variable energy positron beam, spin- polarized positron annihilation spectroscopy and the measured field reversal asymmetry can be used to do magnetic depth profiling in magnetic materials and thin films.
Primary author
Ali R. Koymen
(University of Texas at Arlington)
Co-authors
Prof.
Alex H. Weiss
(University of Texas at arlington)
Mr
Alex J. Fairchild
(University of Texas at arlington)
Dr
Varghese Anton Chiarayath
(Unversity of Texas at arlington)
