Introduction to the Physics of Diluted Magnetic Semiconductors

Diluted magnetic semiconductors, or semimagnetic semiconductors, seemed for a while to be one of those research topics whose glory (i. e. , the period of most ext- sive research) belongedalready to the past. This particularlyapplied to ¿traditional¿ diluted magnetic semiconductors, i. e. , substitutional alloys of either II¿VI or IV¿VI semiconductors with transition metal ions. Fortunately, a discovery, in the beg- ning of the nineties [1,2], of ferromagnetic ordering in III¿V DMSs with critical temperatures reaching 170 K has renewed and greatly intensi ed an interest in those materials. This was, at least partially, related to expectations that their Curie temperatures can be relatively easily brought to room temperature range through a clearly delineatedpath and,partially,due to the great successes, also commercial,of metallic version of spintronics, which earned its founders the Nobel Prize in 2007. The semiconductor version of spintronics has attracted researchers also because of hopes to engage it in efforts to construct quantum information processing devices. While these hopes and expectations are not fully realized yet, the effort is going on. As a goodexampleof recentachievements,new resultson quantumdotsconta- ing a single magnetic ion should be mentioned. A great progress has been achieved in studies of excitonic states in such quantum dots, so far limited to InAs/GaAs [3,4] and CdTe/ZnTe [5,6] material systems and to Manganese as the magnetic ion. Furthermore, in the II¿VI QDs, rst results on the optical control of the Mn spin states havebeenexperimentallydemonstrated[7¿9]andtheoreticallyanalyzed[10]; the studies of Mn spin dynamics and control in III¿V QDs will certainly follow.