THE MAGNETIC STABILITY OF SPIN-DEPENDENT TUNNELING DEVICES

The tunneling resistance between two ferromagnetic metal Layers that a re separated by a thin insulator depends on the relative orientation o f the magnetization M of each Layer. In a memory device, independent s witching of the magnetically soft Layer is achieved by making the othe r Layer either exchange-biased or magnetically hard. The repeated reve rsal of M of the soft Layer by field cycling can demagnetize the other magnetically hard Layer and thus erase the tunnel junction's memory. The M of exchange-biased structures was stable at Least to 10(7) cycle s, whereas in hard structures, M generally decayed Logarithmically wit h the number of field cycles. The decay was very sensitive to the thic kness of the hard Layer and the composition of the soft layer. However , no decay was observed when the moment reversal was accomplished by c oherent rotation, establishing that demagnetization results from the f ormation and motion of domain walls in the soft layer during field cyc ling.