Magnetoresistance and spin-transfer torque in magnetic tunnel junctions

The trapping of electrons by grain boundaries in semiconducting and insulating materials is important for a wide range of physical problems, for example, relating to: electroceramic materials with applications as sensors, varistors and fuel cells, reliability issues for solar cell and semiconductor technologies and electromagnetic seismic phenomena in the Earth's crust. Surprisingly, considering their relevance for applications and abundance in the environment, there have been few experimental or theoretical studies of the electron trapping properties of grain boundaries in highly ionic materials such as the alkaline earth metal oxides and alkali halides. Here we demonstrate, by first-principles calculations on MgO, LiF and NaCl, a qualitatively new type of electron trapping at grain boundaries. This trapping is associated with the negative electron affinity of these materials and is unusual as the electron is confined in the empty space inside the dislocation cores.

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Electron-trapping polycrystalline materials with negative electron affinity.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1020&context=physicstsymbal

Interface effects in spin-polarized metal/insulator layered structures

Interlayer Exchange Coupling in Fe|MgO|Fe Magnetic Tunnel Junctions

An exchange bias phenomenon not present in bulk ferromagnetic systems is now observed at the Fe/MgO interface.

Exchange bias of the interface spin system at the Fe/MgO interface

We report scanning tunneling spectroscopy studies of the electronic structure of 1.5 to 3 nm (001) textured MgO layers grown on (001) Fe. Thick MgO layers exhibit a bulk-like band gap, approximately 5-7 eV, and sparse, localized defect states with characteristics attributable to oxygen and, in some cases, Mg vacancies. Thin MgO layers exhibit electronic structure indicative of interacting defect states forming band tails which in the thinnest case extend to approximately 0.5 V of the Fermi level. These vacancy defects are ascribed to compressive strain from the MgO/Fe lattice mismatch, accommodated as the MgO grows.

J. C. Read

Papers

Disorder, defects and bandgaps in ultra thin (001) MgO tunnel barrier layers