B. Szymański

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.

The influence of sublayer thickness on GMR and magnetisation reversal in permalloy/Cu multilayers

Abstract It has been shown that in Py/Cu (Py = Ni 87 Fe 17 , permalloy) multilayers obtained by face-to-face sputtering technology, two well-separated antiferromagnetically coupled ranges can be found centered at d Cu ≈ 1 and 2 nm, respectively. However, d Cu values corresponding to the largest field sensitivity of the GMR effect are different from those for which the strongest antiferromagnetic exchange coupling has been found. With decreasing Py thickness, the magnetic properties become strongly influenced by the magnetisation fluctuations. We attribute this effect to the presence of compositionally intermixed interfaces. Changes in the magnetic properties and magnetoresistance as a function of Py thickness are analysed in terms of evolution from paramagnetic through superparamagnetic to ferromagnetic behaviour of these intermixed regions.

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.

Magnetic properties of electrolytic Co-Pd alloy films

A method has been developed to produce Co100−xPdx (40 < x < 90) alloy films by electrodeposition from a single bath. In Pd-rich composition (70 < x < 85 at %) we have observed strong perpendicular magnetic anisotropy, attributed to the stress-induced anisotropy due to tensile stresses introduced into the magnetostrictive films during electrodeposition.

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.

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.

Influence of the Ar-ion irradiation on the giant magnetoresistance in Fe/Cr multilayers

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in Fe/Cr multilayers exhibiting the giant magnetoresistance (GMR) effect is studied by the conversion electron Mossbauer spectroscopy (CEMS), vibrating sample magnetometer hysteresis loops, magnetoresistivity, and electric resistivity measurements and supplemented by the small-angle x-ray diffraction. The increase of Ar-ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step sites detected by CEMS. The modification of microstructure induces changes in magnetization reversal indicating a gradual loss of antiferromagnetic (AF) coupling correlated with the degradation of the GMR effect. Distinctly weaker degradation of AF coupling and the GMR effect observed for irradiated samples with a thicker Cr layer thickness suggest that observed effects are caused by pinholes creation. The measurements of temperature dependence of remanence magnetization confirm increase of pinhole density and sizes during im...

The effect of magnetostatic coupling on spin configurations in ultrathin multilayers

(Co/Au)N ultrathin multilayers with perpendicular and in-plane magnetic anisotropy were studied experimentally using a combination of ferromagnetic resonance, magneto-optical magnetometry and microscopy (with both in-plane and out-of-plane magnetization-sensitive longitudinal and polar Kerr effects), and magnetic force microscopy (MFM). Three-dimensional magnetization distributions were reconstructed from micromagnetic simulations complemented by the measured magnetic parameters of the multilayers and observations by Kerr microscopy and MFM. It is shown that, in the reorientation phase transition (RPT) zone – the range of anisotropy characterized by 0 < Q < 1 (the ratio of the anisotropy energy to be gained by magnetization along the easy axis perpendicular to the sample surface, and the magnetostatic energy of a uniformly magnetized layer along the surface normal) – the three-dimensional magnetization distributions consist of alternating pairs of vortices and half-antivortices, both with in-plane magneti...

Magneto-optical spectroscopy study of the solid-state reaction in Ti'Ni multilayered films

A comparative study of the solid-state reaction (SSR) in a series of Ti/Ni multilayered films (MLF) with a bilayer period of 0.65–22.2 nm and constant Ti to Ni sublayer thickness ratio has been performed by magneto-optical (MO) spectroscopy as well as x-ray diffraction (XRD). The spectral and sublayer-thickness dependences of the MO properties of the Ti/Ni MLF were explained on the basis of the electromagnetic theory. A threshold nominal Ni-sublayer thickness of about 3 nm in the as-deposited Ti/Ni MLF is necessary for observing the equatorial Kerr effect. Such a fact is explained by the formation, by solid-state reaction, of nonmagnetic alloyed regions between pure components. The SSR in the Ti/Ni MLF caused by the low temperature annealing leads to a formation of an amorphous Ti/Ni alloy and takes place mainly in Ti/Ni MLF with “thick” sublayers. In the case of Ti/Ni MLF, MO turns out to be more sensitive in determining the thickness of the reacted zone, while XRD is more useful for the structural analy...