• Sessi, V.; Hertenberger, S.; Zhang, J.; Schmitz, D.; Gsell, S.; Schreck, M.; Morel, R.; Brenac, A.; Honolka, J.; Kern, K.: Exchange bias in reduced dimensions: Cobalt nanocluster arrays under the influence of nanometer thin MnPt capping layers. Journal of Applied Physics 113 (2013), p. 123903/1-10

10.1063/1.4795274

Abstract:
The magnetic behavior of cobalt nanocluster arrays arranged on a boron-nitride nanomesh and capped with MnPt layers of varying thickness is investigated. The magnetic properties of the arrays are found to be strongly dependent on the cobalt nanocluster size: large 3-dimensional clusters of several nanometers size under the influence of only 5 nm MnPt exhibit prototypical exchange bias behavior, whereas small 2-dimensional clusters of about 1 nm in diameter show superparamagnetic behavior, however, with a strong quenching of the average cobalt magnetization. The latter effect is correlated with the formation of a stable antiferromagnetic phase at increasing MnPt thickness and is discussed in terms of the domain state exchange bias model. The quenching suggests either partial antiferromagnetic alignment of cobalt spins within a cluster or a random orientation of cobalt cluster macrospins with respect to each other.