  Co(x nm, x=10nm or 40nm)/Cu(5nm)/Co(2.5nm) layers were deposited between
copper electrodes in SiO2 vias. Magnetic states, and the corresponding
resistance states, of these devices were switched by electric currents
perpendicular to the layers. The I-V loops show asymmetric behavior with
hysteresis. When electrons flow in the direction from thick to thin Co layer
(positive current), multiple switches were observed on increasing current up to
a chosen maximum positive I(write). On decreasing current from I(write), the
I-V curve was smooth and characterized by considerably lower resistance. Under
reverse current, an abrupt switch to the high resistance state occurred at the
current value I(erase)~ -0.9*I(write). Resistance had a maximum at zero current
in both states, where the ratio R(high)/R(low) could be as high as factor of
four.
