Temperature and size dependence of antiferromagnetism in Mn nanostructures

We report on variable-temperature STM investigations of the spontaneous long-range magnetic order of Mn monolayer nanostructures epitaxially grown on stepped W(110). The measurements reveal that the onset of the antiferromagnetic order is closely related to the Mn nanostructure width along the [001] direction, with a decreasing N{\'e}el temperature as we move from a 2D toward a quasi-1D system. In contrast, lateral confinement along the [$1\overline{1}0$] direction seems to play a less important role. The results are discussed in terms of anisotropic exchange coupling and of boundary effects, both potentially stabilizing long-range magnetic order in nanostructures confined in the [$1\overline{1}0$] direction.