Emergence of noncollinear magnetic ordering in small magnetic clusters: Mn${}_n$ and As@Mn${}_n$

Using first-principles density functional calculations, we have studied the magnetic ordering in pure Mn${}_n$ ($n=2-$10, 13, 15, 19) and As@Mn${}_n$ ($n=1-$10) clusters. Although, for both pure and doped manganese clusters, there exists many collinear and noncollinear isomers close in energy, the smaller clusters with $n⩽$5 have collinear magnetic ground state and the emergence of noncollinear ground states is seen for $n⩾$6 clusters. Due to strong $p-d$ hybridization in As@Mn${}_n$ clusters, the binding energy is substantially enhanced and the magnetic moment is reduced compared to the corresponding pure Mn${}_n$ clusters.