Topological phase of the interlayer exchange coupling with application to magnetic switching

We show, theoretically, that the phase of the interlayer exchange coupling (IEC) undergoes a topological change of approximately $2\pi$ as the chemical potential of the ferromagnetic (FM) lead moves across a hybridization gap (HG). The effect is largely independent of the detailed parameters of the system, in particular the width of the gap. The implication is that for a narrow gap, a small perturbation in the chemical potential of the lead can give a sign reversal of the exchange coupling. This offers the possibility of controlling magnetization switching in spintronic devices such as MRAM, with little power consumption. Furthermore we believe that this effect has already been indirectly observed, in existing measurements of the IEC as a function of temperature and of doping of the leads.