The effects were investigated of carbon ion dose on the exchange field and GMR ratio of irradiated PtMn-based spin valves. The exchange field increases with increasing dose in the low ion-dose-regime, which is attributed to the increase in PtMn(C) formation. The maximum enhancement of the exchange field can be as large as 50 for the ion dose of 2.0 × 10{sup}14 ions/cm{sup}2. The reduction of the exchange field in the high-dose regime is probably due to the intermixing or carbon residue at the interface. The giant magnetoresistance (GMR) ratio monotonically decreases with increasing carbon dose. Ion irradiation shows different effects on fcc and fct PtMn samples. By proper annealing prior to irradiation, we can obtain a large enhanced exchange field and a reasonably good MR ratio.
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