Thursday,
September 24, 2009 - 4:00 P.M., NSH 184
I will review the evolution of II-VI-based diluted magnetic semiconductors (DMSs) from their discovery to the present. Milestones in this road include the creation of materials themselves: first, high-quality HgMnTe, followed by other II-Mn-VI ternary alloys. Next, there were the discoveries of spin effects arising from the presence of Mn in the II-VI lattice: helicon-excited spin resonance; magneto-transport effects such as the spin splitting of Shubnikov-de Haas oscillations; magneto-optical effects (e.g., the giant Faraday effect); and magnetically-induced metal-insulator transition. A theoretical milestone was the identification of sp-d exchange interaction between Mn and band electrons of the II-VI host, accompanied by the discovery of such magnetic effects as the spin glass transition and the bound magnetic polaron.
In the mid-1980’s, it was shown that DMSs can be grown by molecular beam epitaxy (MBE), leading to the era of “designer materials” (e.g., quantum wells, superlattices, and eventually quantum dots and wires) and also laying the foundation for spintronics. For example, the ability to epitaxially interface ZnMnSe with GaAs-based structures resulted in prototype spin-injection devices. Epitaxy also allowed the realization of ferromagnetism in II-Mn-VI quantum wells, similar to the III-Mn-V materials such as GaMnAs.
But most important, the rich interplay between spin and electronic phenomena that occur in II-VI DMSs has brought the semiconductor and magnetism communities closer together. It is this interface of semiconductor physics and magnetism that is the foundation of spintronics.