THEORY OF OSCILLATORY EXCHANGE IN MAGNETIC MULTILAYERS - EFFECT OF PARTIAL CONFINEMENT AND BAND MISMATCH

In an earlier work a theory of the oscillatory exchange coupling betwe en two ferromagnetic layers across a nonmagnetic spacer was proposed. It relied on size-quantization of the energy of electrons of one spin confined in the spacer (complete confinement model). Detailed tight-bi nding calculations of the coupling between Fe layers across Cr(001) us ing five d orbitals and the complete confinement model are reported. T he coupling exhibits oscillations with several different periods but t he amplitude and phase do not agree with experiment. An exactly solvab le hole gas model and new tight-binding results are presented which de monstrate that the oscillation period is unaffected but the amplitude and phase depend critically on the degree of confinement. In particula r, the amplitude is reduced dramatically for a weak confinement approp riate to iron. The dependence of the coupling on the occupancy of the spacer layer d band is also investigated. It is shown that a mismatch between the ferromagnet and spacer layer d bands, which increases with increasing number of holes in the spacer, leads to a systematic varia tion of the coupling strength across the transition metal series in ag reement with experiment.