Journal of Superconductivity: Incorporating Novel Magnetism ( C © 2005) DOI: 10.1007/s10948-005-0005-2 Ferromagnetism of Mn/Ge Multilayers Grown

We report on novel ferromagnetic Mn/Ge multilayers for spintronics applications investi-gated both experimentally and theoretically. Two Mn/Ge multilayers are grown on GaAs (001) substrates by molecular beam epitaxy. The period of each multilayer consists of an Mn layer of varying thickness (0.6 and 5 Å) and a 10 A ̊ thick Ge spacer layer. From temperature-dependent magnetization and hysteresis loop measurements, the Mn (0.6 Å)/Ge (10 Å) mul-tilayer showed very weak ferromagnetic ordering, which is persistent up to 260 K, whereas the Mn (5 Å)/Ge (10 Å) multilayer exhibited strong ferromagnetism up to 305 K. The co-ercive field of the Mn (5 Å)/Ge (10 Å) multilayer was 277 Oe at 200 K. Density functional electronic band structure calculations on a number of Mn/Ge (001) multilayers determined them to be ferromagnetic, and estimates of their critical temperatures are reported. KEY WORDS: Mn/Ge multilayers; ferromagnetism; MBE. Recently, magnetic semiconductors have at-tracted great attention due to the potential to cre-ate new classes of spin-dependent electronic devices. Much interest was generated by the recent discovery of ferromagnetism in III-Mn-V semiconductors [1,2] and heterostructures [3–5]. In this context, the group-IV-based ferromagnetic materials have not been as intensively investigated as their III-V counterparts, in spite of the possibility of integration with the ma-ture Si-based technologies. This important group of semiconductors was rediscovered following the ob-servation that Mn substitution in Ge yields ferromag-netism, with reported Curie temperatures of 116 K [6] and 285 K [7]. Previously, we reported room-temperature ferromagnetism of Ge-based multilayer structures, i.e., Ge/MnAs multilayers [8]. In this ar-ticle, we report ferromagnetism up to 305 K in an Mn (5 Å)/Ge (10 Å) multilayer grown by molecular beam epitaxy (MBE). The Mn/Ge multilayer structures were grown on semi-insulating GaAs (001) substrates in an MBE system, as described in detail elsewhere [9]. The Mn