Spin transport through atomic scale chromium Coulomb islands

Electrical current through metallic islands coupled via tunnel barriers to external leads is governed by the Coulomb repulsion and can be brought down to single electron transport. The spin-degeneracy of the electrons can be lifted by choosing both the leads and the islands to be magnetic. The combination of spin-splitting and Coulomb blockade creates a device geometry capable of resonant tunneling of a single spin-direction only. Maximum effect can be obtained by minimization of the size of the Coulomb islands in order to suppress spin-relaxation. We report on our efforts to make a spin-resonant tunneling device using atomic size clusters of chromium atoms, submerged in an alumina-barrier in a conventional magnetic tunnel junction set-up. The $300x300\;\mu\rm{m}^2$ size magnetic tunnel junction consists of a cobalt bottom electrode, an aluminum-oxide tunnel barrier, a delta-doping layer of chromium in the range of $1-6\;\AA$, an alumina tunnel barrier, and a permalloy top-electrode. Transport measurements reveal Coulomb blockade behavior.