Experimental Observation of Disorder-Driven Hysteresis-Loop Criticality

Abstract

We have studied the effect of magnetic disorder on the magnetization reversal process in thin $\mathrm{Co}/\mathrm{CoO}$ films. 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 $\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.022\ifmmode\pm\else\textpm\fi{}0.006$ and $\ensuremath{\beta}\ensuremath{\delta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.30\ifmmode\pm\else\textpm\fi{}0.03$ for this two-dimensional system.