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Tunneling Anisotropic Magnetoresistance Driven by Resonant Surface States
A. N. Chantis, K. D. Belashchenko, E. Y. Tsymbal, and M van Schilfgaarde Phys. Rev. Lett. 98, 046601 (2007).

The spin-dependent properties of magnetic surfaces has recently been a "hot" topic because of the advent of magnetoelectronics, a.k.a spintronics. Use of scattering at magnetic interfaces has been the main reason why disk drives today are so much higher density than they were ten years ago. Spintronics is a technology aimed at exploiting the electron-spin among with the electron-charge in the design of electron devices. One of the most sucessful are memories bases on Tunneling Magnetoresistance (TMR) junctions. TMR junctions consist of two ferromagnetic electrodes separated by an oxide.

Recently, an experiment suggested that the effect can be realized through a different principle, namely from the orientation-dependence of electron spin. This anisotropy is particularly important near metal/insulator interfaces and was called TAMR (Tunneling Anisotropic Magnetoresistance). This paper explains a mechanism for TAMR, and shows that it can occur by the effect of spin on resonant surface states.

The panels in the Figure show how the electron transmission through a Fe interface changes with the electron momentum in the plane of the interface. Red colors show where the transmission is strong. The figure shows that there is a strong difference between majority and minority transmission (compare top to bottom panels)

Comparing left and right panels shows the dependence on the orientation of the external magnetic field (“anisotropy”) On the left, there is a fourfold symmetry (field perpendicular to the surface); on the right it is broken (field in the plane of the surface). It is responsible for the TAMR. The graph at the bottom shows that the TAMR can be as much as 20%.