Electrical characteristics and Coulomb blockade in Co/Al2O3/NiFe MTJs

Abstract

The electrical characteristics of single-type magnetic tunnel junctions (MTJs), Co/Al2O3/Ni80Fe20, were studied by means of the I-V, G-V, Z complex impedance spectra data along with the Simmons' and Brinkman's fitting procedure. A Coulomb blockade (CB)-like phenomenon was observed in some of the single MTJ samples in the form of periodic peaks in the G-V curves. This effect is attributed to the quantized charge transport through the ferromagnetic "nano-islands" formed within the Al2O3 layer. Artificial island-type MTJs were fabricated by inserting a very thin Co layer into the Al2O3 barrier layer, Co/Al2O3/Co/Al2O3/Ni80Fe20, followed by annealing. The observed CB behavior in these island-type MTJs not only strongly supports the explanation to the described effect in the single MTJs but also demonstrates the possibility to fabricate the MTJs with the intended CB for application. © 2006 Elsevier B.V. All rights reserved.