Magnetic hysteresis of interface-biased flat iron dots

We report a theoretical study of the coercivity and bias of iron dots exchange coupled with an antiferromagnetic substrate. We show that flat dots, with height close to the iron exchange length, and lateral dimensions of a few exchange lengths, exhibit large enhancement of coercivity and exchange bias. For small interface field strength the magnetization reversal is nearly a coherent rotation with symmetrical loops. Interface pinning leads to large reduction in coercivity and asymmetrical loops, if the interface field strength is comparable to the value of the iron exchange field. We discuss the impact of geometrical confinement and interface pinning on the magnetization reversal mechanisms. We show that small area dots with height larger than the exchange length display stronger interface effects.