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 beta = 0.022 +/-0.006 and beta delta = 0.30 +/-0.03. (C) 2001 American Institute of Physics.