
410 Nanosensors: Physical, Chemical, and Biological
TMR devices use the spin valve arrangement of a pinned magnetic layer
and a free magnetic layer. Electrons pass from one layer to the other through
the insulator by quantum-mechanical tunneling. It is common to electrically
connect multiple TMR devices in series to increase the overall resistance and
limit the voltage at each tunnel barrier. Voltages above a few hundred mil-
livolts may damage the thin insulator. The electric current tunnels through
or ows in a direction perpendicular to the layers (CPP) with contacts on top
and bottom of the lm stack.
Depending on the orientation of their m ...