Large magnetic moments and anomalous exchange coupling in As-doped Mn clusters

Abstract

We report electronic and magnetic properties of pure and arsenic-doped manganese clusters from density functional theory using spin-polarized generalized gradient approximation for the exchange-correlation energy. We see for both the cases, noncollinear treatment of spins are indeed necessary. The arsenic atom stabilizes manganese clusters, which is further accompanied by the ferromagnetic $\mathrm{Mn}\text{\ensuremath{-}}\mathrm{Mn}$ coupling for ${\mathrm{Mn}}_{2}\mathrm{As}$ and ${\mathrm{Mn}}_{4}\mathrm{As}$ clusters, resulting in large cluster magnetic moments, 9 and $17\phantom{\rule{0.3em}{0ex}}{\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$, respectively. We show in doped clusters, exchange coupling are anomalous and behave quite differently from the Ruderman-Kittel-Kasuya-Yosida-type predictions. Finally, it is suggested that, if grown in the low temperature MBE, the giant magnetic moments due to ferromagnetic Mn ordering and their large enough exchange coupling parameter in ${\mathrm{Mn}}_{2}\mathrm{As}$ and ${\mathrm{Mn}}_{4}\mathrm{As}$ could play an important role on the ferromagnetism and on the observed large variation in the Curie temperature of the Mn-doped III-V semiconductors.