Electron charge near atomically sharp corrugations at the surfaces of a solid tends to spill out and smoothen the abrupt variation of the positions of the positively charged atomic nuclei. The reason is that electrons are much less localized than nuclei. This has been discussed already some 70 years ago by Smoluchowski [R. Smoluchowski, Phys. Rev. 60, 661 (1941)], and the corresponding effect of charge redistribution near surface corrugations bears his name. The Smoluchowski effect focuses on the total electron charge density. It neglects that electrons-in addition to charge-also carry a spin. We discuss spin-dependent electron spill out and demonstrate in a combined theoretical and experimental work that compelling consequences for spin-polarization and spin-dependent transport arise at the edges of magnetic nanostructures due to the spin-dependent Smoluchowski effect. We find a variation of the tunnel magnetoresistance ratio of more than 20% on a length scale of a few atomic diameters.
Both
quantum and classical behavior of single atomic spins on surfaces
is determined by the local anisotropy of adatoms and their coupling
to the immediate electronic environment, yet adatoms seldom reside
on surfaces alone, and it is generally acknowledged that substrated-mediated
interactions can couple single spins among each other impacting their
magnetic behavior. Here we show that also magnetic anisotropy, which
is usually considered to be a constant determined by the local crystal
field, can be extremely sensitive to such interactions. By the example
of Co dimers on Cu(001) and Pt(001) surfaces we highlight the intricate
interplay of exchange coupling and magnetic anisotropy, providing
a much sought possibility to tune the latter through deliberate adjustment
of the adatoms’ separation. As a technologically relevant implication
we demonstrate the impact of such emergent nonlocal anisotropy on
the hysterectic properties of single-atom magnetization curves.
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