Mn diffusion effect in the exchange biased NiFe/FeMn/NiFe trilayers

We have fabricated NiFe/Mn/FeMn/Mn/NiFe multilayers using ultrahigh vacuum ion-beam deposition system to study the diffusion effect of the inserted Mn on exchange biasing. As the thickness of the Mn layer was changed from 0 to 1.5 nm, the exchange biasing field H-ex(top) at the top interface of FeMn/Mn/NiFe was decreased from 258 Oe to 24 Oe. On the other hand, the H-ex(bottom) was slightly decreased 103 Oe to 78 Oe without a change in the coercive field H-c. Above 1.2 nm, a reverse phenomena of H-ex was observed. After annealing at 200degreesC, the H-ex(top) was increased by almost a factor of 2; however, the H-ex(bottom) did not change. The analyses of x-ray patterns and Auger spectroscopy showed that the abnormal tendency of H-ex(bottom) originated from the diffusion of Mn atoms at bottom interface into the FeMn layer during film growth, and that the Mn was concentrated at the interface by annealing. (C) 2003 American Institute of Physics.