Disorder-driven hysteresis-loop criticality in Co/CoO films

The effect of magnetic disorder on the magnetization reversal process in thin Co/CoO films has been investigated. The antiferromagnetic CoO layer allows a reversible tuning of the magnetic disorder by simple temperature variation. For temperatures above a critical temperature T_c, we observe a discontinuous magnetization reversal, whereas smooth magnetization loops occur for T<T_c. Our measurements establish the existence of a disorder-driven critical point in the nonequilibrium phase diagram. In addition, we observe scaling behavior in the vicinity of the critical point and determine the critical exponents to β=0.022±0.006 and βδ=0.30±0.03.