Interlayer magnetic coupling in metallic multilayer structures

Publisher Website
Google Scholar
Abstract
The Anderson model of local state–conduction electron mixing is applied to the problem of interlayer magnetic coupling in metallic multilayered structures. Two types of coupling, Ruderman-Kittel-Kasuya-Yosida (RKKY) and superexchange arise from this interaction. The RKKY coupling comes only from intermediate states which correspond to spin excitations of the Fermi sea, that is, states corresponding to electron-hole pair production in the Fermi sea with an attendant spin flip. The superexchange coupling arises from virtual-charge excitations in which electrons from local states are promoted above the Fermi sea (one from each layer); this provides a second contribution to the coupling, that is in addition to the RKKY coupling. Moreover, the RKKY coupling is largely influenced by the topology of the Fermi surface and contains oscillatory modes of the coupling while superexchange coupling does not contain much Fermi-surface information. The RKKY coupling is ferromagnetically biased, while the superexchange coupling is antiferromagnetically biased. The total interlayer coupling (RKKY plus superexchange) resembles the oscillatory coupling of magnetic impurities in a free electron gas (the conventional RKKY coupling or Lindhard range function), but is antiferromagnetically biased if the density of states has a relatively large peak just above the Fermi energy. These characteristics are visible in two ways in experimental data: (i) the spin polarization pattern in the spacer layer between magnetic ones can be different from that of the interlayer magnetic coupling, and (ii) some metallic multilayered structures could have relatively large antiferromagnetic biases in their interlayer magnetic coupling; for example, Fe/Cr systems.