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We have investigated, by means of ac susceptibility experiments, the magnetic relaxation of layers of Co nanoclusters (D ≃ 2.6 nm) embedded in Al[SUB2]O[SUB3]. Superparamagnetic blocking takes place at higher temperatures as the number of layers increases. These results are interpreted using a simple model in which dipole--dipole interactions between nearest neighbor particles increase the relaxation time. The influence of interactions is affected by the application of bias magnetic field H. As the magnetic moments of the particles become polarized by H, the blocking temperature approaches the behavior expected for noninteracting particles. [ABSTRACT FROM AUTHOR]

We present experimental results on the displacement of a domain wall by injection of a dc current through the wall. The samples are 1-μm-wide long stripes of a CoO/Co/Cu/NiFe classical spin-valve structure. The stripes have been patterned by electron-beam lithography. A neck has been defined at 1/3 of the total length of the stripe and is pinning center for the domain walls, as shown by the steps of the giant magnetoresistance curves at intermediate levels (1/3 or 2/3) between the resistances corresponding to the parallel and antiparallel configurations. We show by electric transport measurements that, once a wall is trapped, it can be moved by injecting a dc current higher than a threshold current of the order of magnitude of 10[SUP7] A/cm[SUP2]. We discuss the different possible origins of this effect, i.e., local magnetic field created by the current and/or spin transfer from spin-polarized current. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic behavior and the structural properties of ferromagnetic–antiferromagnetic systems (NiFe–IrMn and Co–IrMn) deposited directly on a thin tantalum buffer layer (bottom configuration) or above a thin Al2O3 tunnel barrier layer (top configuration). In the bottom configuration, the bilayer system exhibits higher magnetic performances than in the top configuration in terms of thermal stability. We have performed a detailed structural study by X-ray diffraction and high-resolution transmission electron microscopy which allow us to establish a clear correlation between the situation of the bilayer with respect to the tunnel barrier, its texture and its magnetic properties. [Copyright &y& Elsevier]