Non-collinear coupling between magnetic adatoms in carbon nanotubes

Abstract

The long-range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a noncollinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed on the walls of carbon nanotubes. Our results show that the magnetic coupling cannot be inferred only by total-energy differences between the ferromagnetic and antiferromagnetic configurations, the possibility of noncollinear alignments suggesting this to be a misleading practice