Influence of the nature of the buffer on the coupling and the transport properties in Co/Ru/Co sandwiches Structural, magnetotransport, and optical properties of sputtered Co/Cu multilayers examined as a function of Co layer thickness at the second antiferromagnetic maximum

Cu/AgCo layered granular structures were prepared to study their field transport properties in comparison to their microstructure. The superlattices of the samples were characterized by x-ray diffraction. A combination of random and antiparallel alignments of magnetic particles is discovered expressing an oscillation of interlayer coupling similar to conventional multilayers. The weak antiferromagnetic coupling across thin Cu spacer layers between interfacial Co particles results in a notable enhancement of low-field sensitivity compared to granular single films. The oscillation period obtained here for Cu(111) interlayers is close to 3 atomic layers.

Permalloy (Py:Ni 81 Fe 19 ) exhibits an anisotropic magnetoresistance (AMR) which is very often used to read magnetic signals from storage devices. Py-films of thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to 1000K in order to investigate the dependence of the magnetic anisotropy and the AMR on heat treatments. The films exhibit an uniaxial anisotropy after preparation which changes during annealing above 520K. The AMR along the former magnetically easy axis as well as the corresponding field sensitivity are increased by a heat treatment around 700K reaching maxima of about 8% and a maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of the local atomic order.Known for more than 100 years [1] the anisotropic magnetoresistance (AMR) seemed to be the optimal method to write and read magnetic signals for storage devices. Because of its soft magnetic properties Permalloy (Py:Ni 81 Fe 19 ) was one of the most protruding materials for this purpose. Even though magnetic multilayers [2], granular systems [3], spin valve systems [4] and metal-insulator transition systems [5] nowadays show much higher changes in resistivity by applying a magnetic field it was only shown recently that spin valves [6], discontinuous Py/Ag-multilayers [7] and conventional Py/Au-multilayers [8] could reach field sensitivities of about 1%/Oe which are even higher than the sensitivities obtained from AMR of "pure" Py.Here we discuss the effect of heat treatments on pure Py-films prepared in a magnetic field. It is known [9] that Py annealed at temperatures of 520K and above may exhibit very complicated magnetic properties, especially a change of the anisotropy. This is at about the same annealing temperature at which the magnetoresistive behavior of the discontinuous multilayers starts to change [7,10]. II. EXPERIMENTAL DETAILSPy-films of thickness 20nm were dc-magnetron sputtered at ambient temperatures onto thermally oxidized Si-wafers. The background pressure and the Ar pressure during preparation were 1x10 -8 mbar and 9x10 -3 mbar, respectively, the deposition rate was 3.0nm/s. The total thickness was controlled ex situ by small angle X-ray diffraction measurements. Because the distance between target and substrate is only 5 cm, the films are sputtered within the stray field of the Py-target and the magnets of the sputter gun. In this distance we measure a maximum static magnetic field of 15x10 -4 T using a Hall device. Because of the rotational symmetry of our sputtering device and one single rotation of the substrate underneath the target during the entire film preparation, this field changes its direction relative to the sample position during the sputter process and therefore with film thickness. After preparation the wafers are cut into