Grain-size effects in exchange-biased FeMn/NiFe bilayers

FeMn/NiFe exchange-biased films have been deposited on Si substrates and the average grain size in the antiferromagnet systematically varied from 54 to 70 Å. Vibrating-sample magnetometer measurements at room temperature show that the exchange field increases by a factor of about 3 with increasing grain size. Changes in the coercivity were much smaller. We believe the grain-size effects are due to thermal activation phenomena. Training effects give rise to a greater reduction in the exchange field for the system with the smallest grains. The absence of a significant change in the coercivity implies that it is primarily controlled by interfacial effects.