Probing Oscillatory Exchange Coupling with a Paramagnet

A paramagnet is used to probe directly the exchange coupling emanating from a ferromagnetic specimen across a nonmagnetic spacer material. The model structure to observe the oscillatory exchange field consists of a Cu(100) single crystal, a Co base layer, a Cu spacer, and fcc Fe as the paramagnetic probe layer with large magnetic susceptibility. We find that, if the spacer layer is sufficiently thin, even paramagnetic fcc Fe films are magnetically polarized in-plane at room temperature. Spin-resolving techniques show that the magnetization of the paramagnet oscillates as a function of the spacer thickness. For constant Cu spacer thickness the spin polarization changes sign when the thickness of the Fe overlayer is varied. Thus the paramagnetic fcc Fe overlayer serves both as a marker of exchange oscillations and as an additional spacer.