No abstract

Antiferromagnetic coupling between ferromagnetic layers has been observed for the first time in an all-semiconductor superlattice structure EuS/PbS(001), by neutron scattering and magnetization measurements. Spin-dependent superlattice band structure effects are invoked to explain the possible origin and the strength of the observed coupling.

A spin-pair model including magnetoelastic terms to second order in strain is used to analyze the magnetic anisotropy of epitaxial Cu/Ni/Cu/Si͑001͒ films. Two adjustable parameters are used to fit the magnetic anisotropy data taken by a torque magnetometer. It is found that the nonlinear bulk magnetoelastic term can contribute up to about 40% of the total anisotropy energy for thinner nickel films.

The applicability of the strain-induced bcc phase of Co in magnetoresistive devices was studied. Ultrathin bcc Co͑001͒ films and the influence of the additional layers needed for magnetoresistive devices were examined by means of 59 Co nuclear magnetic resonance ͑NMR͒. NMR is shown to be a discriminating technique for determining the presence of structurally and magnetically pure bcc Co. The maximum stability for uncovered and Fe-covered layers grown on Fe͑001͒/GaAs͑001͒ and Fe͑001͒/Ge͑001͒ seed layers is found to be about 2 nm. Growth of an Al 2 O 3 top layer preserves the bcc phase, in contrast to a Cu film which causes a transformation of the bcc structure to the fcc or the hcp phase. The bcc-preserving effects of Al 2 O 3 imply the possibility to fabricate magnetic tunnel junctions with bcc Co͑001͒ bottom electrodes. Although bcc Co is a force-induced structure, thin layers are shown to be stable over a few years when Al 2 O 3 has been grown on top. Junction structures using bcc Co͑001͒ bottom electrodes were grown and characterized.

The magnetic anisotropy of epitaxial Cu(50 Å)/Ni(tNi/Cu(2000 Å)/Si(001) films as a function of the nickel film thickness (30 Å⩽tNi⩽150 Å) has been studied using a torque magnetometer. It is found that the magnetization rotates continuously from out-of-plane to in-plane as the nickel film thickness increases. For the 150 Å film, the magnetization cants at 42° with respect to the film normal. The canting state is possible because K4eff is positive. The magnitude of K4eff (≈105 ergs/cm3) is an order of magnitude greater than the corresponding magnetocrystalline anisotropy constant of nickel. The origin of the fourth-order anisotropy in these films is believed to be magnetoelastic in nature.