M. Urbaniak

Magnetic and magnetoresistive properties of NiFe/Au/Co/Au multilayers with perpendicular anisotropy of Co layers

The giant magnetoresistance (GMR), magnetization reversal, and domain structure of magnetron sputtered spin valve [NiFe/Au/Co/Au]N multilayers consisting of ferromagnetic layers with alternating in-plane (NiFe) and out-of-plane (Co) magnetic anisotropy has been investigated. For 0.4 3, the neighboring magnetic layers were observed to be coupled. This coupling is of magnetostatic origin. The effective coupling field, estimated from GMR dependencies, is of the order of 100 kA/m. Micromagnetic simulations confirm that the domain structure of Co layers influences the behavior of NiFe layers.

Magnetic field induced transition from weak to strong ferromagnetic coupling in NiFe∕Au∕Co∕Au multilayers

We report on a specific magnetostatic coupling in sputter deposited (Ni80Fe20∕Au∕Co∕Au)10 multilayers of alternating in-plane and out-of-plane magnetic anisotropies. We demonstrate on the basis of complementary studies (magnetoresistance, conventional magnetometry, and element specific soft x-ray resonant magnetic scattering hysteresis measurements) that the magnetization reversal of the Ni–Fe layers is strongly influenced by a magnetostatic coupling originating from the out-of-plane stripe domain stray fields of the Co layers.

Co/Au multilayers with graded magnetic anisotropy for magnetic field sensing

A concept of a magnetoresistive sensor for magnetic fields based on a Au/Co-wedge/Au/Co/Au multilayer is proposed. The wedged Co layer is characterized by a laterally changing coercivity resulting from a gradient of perpendicular magnetic anisotropy. Its magnetization reversal in a perpendicular magnetic field takes place by movement of a single domain wall in the direction parallel to the anisotropy gradient. The magnetization reversal of the multilayer has been investigated by magnetooptical and magnetoresistive measurements. The resistance of the proposed film system correlates well with the position of the domain wall and thus it can be used to sense magnetic fields.

Colloidal domain lithography for regularly arranged artificial magnetic out-of-plane monodomains in Au/Co/Au layers.

Regularly arranged magnetic out-of-plane patterns in continuous and flat films are promising for applications in data storage technology (bit patterned media) or transport of individual magnetic particles. Whereas topographic magnetic structures are fabricated by standard lithographical techniques, the fabrication of regularly arranged artificial domains in topographically flat films is difficult, since the free energy minimization determines the existence, shape, and regularity of domains. Here we show that keV He(+) ion bombardment of Au/Co/Au layer systems through a colloidal mask of hexagonally arranged spherical polystyrene beads enables magnetic patterning of regularly arranged cylindrical magnetic monodomains with out-of-plane magnetization embedded in a ferromagnetic matrix with easy-plane anisotropy. This colloidal domain lithography creates artificial domains via periodic lateral anisotropy variations induced by periodic defect density modulations. Magnetization reversal of the layer system observed by magnetic force microscopy shows individual disc switching indicating monodomain states.

High sensitivity GMR with small hysteresis in Ni-Fe/Cu multilayers

Abstract Giant magnetoresistance (GMR) effect and magnetisation reversal processes have been investigated in Py/Cu(Py=Ni 83 Fe 17 , permalloy) multilayers (Mls) obtained by face-to-face sputtering method. The investigated films had constant sublayer thicknesses both for Py and Cu (d Cu =2 nm, d Py =2 nm) and various numbers of ferromagnetic sublayers. It has been shown that for such Mls a high field sensitivity of GMR effect (S≈0.4%/Oe) and negligible hysteresis can be obtained for a low number of Py layers.

Antiferromagnetic magnetostatic coupling in Co/Au/Co films with perpendicular anisotropy

Magnetization reversal processes in Au/Co/Au-wedge/Co/Au pseudo-spin-valve structures characterized by perpendicular anisotropy of 0.6-nm-thick Co layers were investigated by magneto-optical Kerr effect. The samples were deposited on a Ti/Au buffer layer of differing Au-layer thickness (different surface roughness and crystallite size). The distinctive influence of the buffer layer thickness on the dependences of switching fields, and energy of the effective interlayer coupling, versus Au spacer thickness is presented. In particular, increasing the buffer-layer thickness results in a decrease in the oscillation amplitude of the Ruderman–Kittel–Kasuya–Yosida-type interaction and in the enhancement of the antiferromagnetic coupling related to magnetostatic (orange peel) interactions.

Creation of Out-of-Plane Magnetization Ordering by Increasing the Repetitions Number

The influence of the Co layer thickness as well as the number of repetitions N on the magnetic properties of (Co/Au)N multilayers was investigated systematically using magneto-optical techniques, vibrating sample magnetometry, and magnetic force microscopy. The studies focused on the characteristics of magnetic hysteresis loops in connection with magnetic domain structure parameters. Increasing the repetitions number, an out-of-plane magnetization ordering is created for Co layers with a thickness larger than the single-layer thickness at which the spin reorientation transition occurs.

N

Material selective sensitivity of a magneto-optical polar Kerr effect to magnetizations of films from different materials in a multilayer system is presented. The method is supported by rigorous modeling of magneto-optic response from the multilayer system and by experimental demonstration on the periodic cobalt-permalloy multilayers [Ni80Fe20(2 nm)/Au(2 nm)/Co(0.4, 0.8, and 1.2 nm)/Au(2 nm)]10 .

in (Co/Au)

The influence of magnetostatic coupling on the magnetic structure in sputter-deposited [Ni80Fe20/Au/Co/Au]N multilayers was studied by magnetoresistance and Mossbauer spectroscopy. The remanent magnetization configuration revealed by Mossbauer measurements correlates well with the results obtained from the magnetic field dependence of resistance. This correlation is observed for samples with Co layers having strong perpendicular anisotropy. Micromagnetic simulations qualitatively explain the observed behavior.

_{\rm N}

Magnetic hysteresis of [NiFe/Au/Co/Au]N multilayers displaying giant magnetoresistance was analyzed by using micromagnetic simulation. It was found that magnetostatic fields of stripe domains in Co layers, with a perpendicular magnetic anisotropy, lead to a replication of those domains in a magnetic configuration of NiFe layers possessing an in-plane shape anisotropy. It was shown that a local minimum of resistance versus an external magnetic field is a signature of the domain replication in systems with alternating perpendicular and the in-plane anisotropies.