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We investigated the molecular beam epitaxy growth, the structure and the magnetic properties of the exchange coupled CoO/Fe bilayers on Ag(0 0 1). In situ X-ray scattering shows that Fe grows in registry with Ag(0 0 1) with an out-of-plane lattice parameter that varies with the Fe layer total thickness. The growth of CoO to build an exchange coupled CoO/Fe system impacts the Fe layer even at room temperature. Two different bilayers grown under close conditions are studied. They differ by the ratio of the oxidized Fe layers over the 7 initial Fe monolayers (30% and 40% respectively). Low temperature exchange magnetic coupling with a blocking temperature T B of about 180 K–150 K and similar thermal behavior are observed for the two samples. We studied one sample with synchrotron X-ray resonant magnetic scattering confirming that the magnetization was perpendicular to the surface below T B . Noteworthy, we found that the magnetic easy axis was lying in-plane at room temperature, above T B . These results point to another example of perpendicular ferromagnetism in an ultra-thin film due to an exchange mechanism with an antiferromagnetic layer that rotates the magnetic easy axis from in-plane to perpendicular below T B .

We report here that in perpendicular tunnel junction the hard layer demagnetizes when the soft layer is cycled. This happens faster when the cycling field is closer to the reversal field of the hard layer. Magnetic force microscopy imaging done at different stages of the cycle after several loops show compact demagnetized areas surrounded by large saturated zones in the hard layer. A mechanism based on interlayer magnetostatic coupling induced by the stray field created by domain wall in the soft layer is presented.

We investigate thermally activated domain wall creep in a system consisting of two ultrathin Co layers with perpendicular anisotropy coupled antiferromagnetically through a 4 nm thick Pt spacer layer. The field driven dynamics of domain walls in the softer Co layer have been measured while keeping the harder Co layer negatively saturated. The effect of the interlayer interaction on the soft layer is interpreted in terms of an effective coupling field, H J , which results in an asymmetry between the domain wall speeds measured under positive and negative driving fields. We show that creep theory remains valid to describe the observed wall motion when the effective coupling field is included in the creep velocity law as a component of the total field acting on the wall. Using the resultant modified creep expression, we determine a value for the effective coupling field which is consistent with that measured from the shift of the soft layer's minor hysteresis loop. The net antiferromagnetic coupling is attributed to a combination of RKKY and orange-peel coupling.

Au/Co(4–8 ML)/Au single magnetic layers and Au(8 ML)/Co(4 ML)/Au(8 ML)/Co(8 ML)/Au bilayer were sequentially grown by electrodeposition on an Au(1 1 1) buffer layer electrodeposited on Si(1 1 1). The technique used in this work provides full control on the structure and the chemical composition of the different layers (no alloying) as well as on the chemistry at interfaces. scanning tunneling microscopy (STM) and atomic force microscopy (AFM) imaging and X-ray diffraction measurements show that atomically flat continuous Co(0 0 0 1) layers (4–8 ML) can be grown in epitaxy with the Au(1 1 1) substrate and that the 2 nm-thick spacer is also a continuous Au(1 1 1) layer. The Co ultrathin layers (4 and 8 ML) exhibit perpendicular magnetic anisotropy. The lateral magnetic homogeneity and magnetization reversal process have been investigated by scanning magneto-optical Kerr effect (MOKE) magnetometry and global Kerr microscopy. The correlation between magnetization switching behaviour in each layer of the Co-bilayer stack has been evidenced from in-depth sensitive MOKE measurements and microscopy. The strong coupling observed between the two Co layers is attributed to magnetostatic interaction at domain wall boundaries.

Extraordinary Hall effect was used to detect the propagation of a coherent 1D Bloch-like domain wall (DW) in submicron structures based on Pt/Co( t Co =1 nm)/Pt sandwiches. We found that the device geometry such as its shape and its size strongly affects DW dynamics. By introducing artificial defects by the use of nano-lithography techniques, we clearly demonstrate that it is possible to accurately control the magnetization reversal process in such mesocopic wires.

It has been recently shown that Co can grow epitaxially on an Au(1 1 1) layer with a face centered cubic (FCC) structure, the Co[1 1 1] and Au[1 1 1] axes being oriented along each other. First magneto-optical studies of the FCC Co film structure are reported here. The differences in magnetic behavior for FCC and HCP-type Co films as a function of the layer thickness are underlined and interpreted in the framework of a phenomenological model.

The second harmonic generation (SHG) reflectivity on magnetic multilayers is a very sensitive technique to reveal the crystallography of buried interfaces. We have used the azimuthal anisotropy of SHG to demonstrate that the vicinal character of Si(1 1 1) substrate is duplicated in the metallic multilayer Au/Co/Au/Cu. The magnetic properties of these multilayers as anisotropy and magneto-optic polar Kerr rotation were studied by linear magneto-optic effects in correlation with SHG experiments, by varying the Co and Au buffer thicknesses as well as the Cu buffer deposition condition.

We create mesoscopic point and line defects by scanning probe lithography to control the magnetization reversal process in Pt/Co/Pt ultra thin film devices. The domain wall propagation near the defects is studied by the Kerr microscopy and extraordinary Hall effect measurements. The observed domain wall pinning is used to block and channel the domain expansion and to create artificial domain patterns.

A low concentration of cobalt clusters with a fcc structure and containing almost one thousand atoms are embedded in two different metallic matrices: platinum and niobium. Samples have been prepared using a co-deposition technique. Cobalt clusters preformed in the gas phase and matrix atoms are simultaneously deposited on a silicon substrate under Ultra High Vacuum conditions. This original technique allows to prepare nanostructured systems from miscible elements such as Co/Pt and Co/Nb in which clusters keep a pure cobalt core surrounded with an alloyed interface. Magnetic measurements performed using a Vibrating Sample Magnetometer (VSM) reveal large differences in the magnetic properties of cobalt clusters in Pt and Nb pointing out the key role of cluster/matrix interfaces.

Ferrosmectics are magnetic liquid crystals which consist of a lyotropic lamellar phase in which colloidal particles of maghemite are incorporated. The rotational dynamics of the colloidal particles is studied by measuring the linear birefringence relaxation of an oriented ferrosmectic sample submitted to a pulse of magnetic field. Two characteristic time scales are found for the relaxation rate. The shorter (∼5 μs) is the characteristic Brownian relaxation time of the particles in the isotropic colloidal suspension (ferrofluid). The slow evolution (∼15 ms), due to the presence of the lyotropic matrix, can be interpreted as due to the adsorption of some particles on the surfactant layers.

We present a study of the structural and magnetic effects induced by focused 30 keV Ga + ion beam irradiation on a Pt(2.8 nm)/[Pt(0.6 nm)/Co(0.3 nm)] 6 /Pt(6.5 nm) ferromagnetic multilayer, using transmission electron microscopy, optical and magneto-optical microscopy. The work is of relevance to high-density data-storage applications, where media planarity is crucial for device reliability.

Ion irradiation is an original process to pattern the structural and as a consequence the magnetic properties of ultra-thin films, down to the nanometer scale. Patterns of dots and tracks have been fabricated by focused Ga + ion beam scanned onto a Co layer with perpendicular magnetic anisotropy. Depending on the dose, the magnetic behaviour of the nanometric irradiated lines can be tuned from the ferromagnetic with reduced coercivity to paramagnetic. The larger the fluence, the smaller is the exchange between dots or tracks. These systems enabled investigations of the competition between exchange and dipolar interactions. For arrays designed with high irradiation doses and only coupled by dipolar interactions, the magnetic relaxation proceeds by the magnetization reversal of individual dots and follows a power-law time decay. Monte Carlo simulations reproduce this time dependence.

We studied individual magneto-optic (MO) contributions of [Tb/Fe] n multilayers in novel {[Tb/Fe] n /Si 3 N 4 } N structures displaying a considerable enhancement of Kerr and Faraday MO effects in red light. A strong sensitivity of individual MO contributions to photon energy is demonstrated and confirmed by an optical multilayer model. This allows us to probe selectively the magnetism of individual stacked multilayers.

Thermomagnetic writing of domains has been performed in a [Tb(8 A)/Fe(10 A)]7 multilayer and studied by magneto-optical microscopy. The nucleation process has been studied using the Huth energy model. Introduction of the Tb/Fe thermal and magnetic characteristics gives very good agreement with experiment. It is also clear from the calculation that the stable domain diameter appears during the cooling phase and not at the end of the laser pulse.

EPR has been performed in this compound at 9.2 and 14.7 GHz between 1.6 and 300 K. The linewidth increases when T decreases, and a lineshift appears below 10 K; they show an anomaly close to T G and are frequency independent; below 10 K, they behave similarly to amorphous metallic spin-glasses.