Hot Electron Spin Valve

A surprising "hot electron spin valve effect" [EPG Pub# 621] was observed in Fe/(Ag, Au, or Cr)/Fe(100) sandwich structures which was manifested as secondary electron intensity oscillations that depended on the relative alignment of the two magnetic layers.

Close inspection of secondary electron intensity images of Fe/(Ag, Au and Cr)/Fe(100) sandwich structures reveal intensity oscillations that appear to be correlated with oscillations in the magnetic exchange coupling. An example of this phenomena is presented in the figure which shows intensity and magnetization SEMPA images from an Fe/Ag/Fe(100) multilayer. Note that the changes in intensity are correlated with oscillations in the exchange coupling and do not depend on magnetization directions. The line scans show intensity and magnetization oscillations for Ag, Au and Cr spacer layers.

Based on these observations, we ascribe this new effect to the spin dependent transport of secondary electrons from the Fe whisker substrate through the spacer and Fe overlayers. This filtering of the secondary electrons is directly analogous to explanations of the basis for the giant magnetoresistance (GMR) in similar sandwich structures. The emission of secondary electrons from the Fe substrate through the Fe overlayer depends on the polarization of the secondary electron spins relative to the Fe overlayer magnetization. The electron transport is favored for parallel alignments. The primary difference between this emission and GMR is the energy of the electrons. GMR phenomena are related to Fermi energy electrons while those playing a role here have energies of about 10 eV higher. The magnitude of the observed intensity fluctuations, on the order of a few percent, makes this effect a promising candidate for use as a spin polarization analyzer.

Hot Electron Spin-Valve Effect in Coupled Magnetic Layers

John Unguris
Robert J. Celotta
Daniel T. Pierce

Michael Kelley - NIST
David Tulchinsky - Naval Research Laboratory

Supported in part by the Office of Naval Research

Online: May 1996
Last Updated: February 2008

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