Magnetic Tunneling Junctions — Materials, Geometry and Applications

Summary

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying standard thin film system with special regard to complex interdiffusion properties. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co₂MnSi, where we obtain up to 100% TMR at low temperature. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm². The last part will give a short overview on field programmable logic circuits made from magnetic tunnelling cells, where we demonstrate the clocked operation of a programmed AND gate.

Research Center Karlsruhe GmbH, Institute for Nano-Technology, PO Box 3640, 76021 Karlsruhe, Germany