Concentration dependence of the exchange interaction in lead europium sulfide nanocrystals

Exchange interactions in nanocrystalline forms of the dilute magnetic semiconductor lead europium sulfide (PbxEuyS), as a function of europium concentration, were investigated using low temperature, high magnetic field vibrating sample magnetometry. The results were fitted to an expression containing a modified Brillouin function, which characterized the response of isolated magnetic europium ions and ion pair interactions. The pair exchange constant J p k B depended weakly on the europium content y. This property may be explained by the existence of larger clusters of Eu2+ ions in PbxEuyS nanocrystals, with the number of clusters increasing with europium content.