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The perpendicular magnetic anisotropy (PMA) of Pt/CoFe(B)/MgO bottom electrodes and the tunnel magnetoresistance (TMR) of CoFeB-based magnetic tunnel junctions (MTJ) have been analyzed as a function of Mg thickness for naturally oxidized barriers. Low PMA and TMR values are found for over-oxidized (small MgO thickness) and under-oxidized (large MgO thickness) barriers. When CoFe is used as bottom electrode, a strong correlation is observed between TMR and PMA variation as a function of MgO thickness with maxima in both quantities occurring for an MgO thickness around 1.2 nm. On the contrary, for CoFeB bottom electrodes, the sensitivity of PMA to MgO thickness is completely lost, as a probable consequence of boron diffusion towards the MgO interface.

Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpendicularly magnetized MgO tunnel junctions. This coupling becomes less negative with increasing annealing temperature up to 375degC. This can be possibly related to homogeneization of oxygen in the barrier and de-oxidation of the magnetic electrodes. However, the evolution of coupling field with both barrier and electrode thickness doesn't agree with existing coupling theories. Similar structures with in-plane magnetized electrodes exhibit classical ferromagnetic coupling.

Sputtered (Pt-Co)/sub n/-FeMn multilayers exhibit both perpendicular magnetic anisotropy and exchange bias at room temperature. Their magnetic properties after in-plane and perpendicular-to-plane magnetic annealing have been studied by means of extraordinary Hall effect and magnetic force microscopy or polar Kerr microscopy. A crossover from in-plane to perpendicular anisotropy was observed as a function of number of repeats n. The dynamics of magnetization switching has been investigated on both sides of the hysteresis loops. A clear asymmetry exists in the dynamics depending whether the field is parallel or antiparallel to the exchange bias field. Similarly, strong differences in the domain patterns at the coercive field were observed. Exchange-biased (Pt-Co)-Pt-(Pt-Co)-FeMn spin-valves were also investigated. Well-separated hysteresis loops were associated with the "soft" and pinned components of the stack. These structures were used to study the interlayer coupling through the Pt spacer.

We have investigated a very efficient way to produce patterned media for ultrahigh density magnetic recording by first preparing patterned wafers made of silicon. Two ways of patterning the wafers were investigated: direct e-beam lithography with reactive ion etching and nanoimprinting. Features as small as 30 nm with a pitch of 60 nm were realized by nanoimprint. Subsequently, a magnetic material was deposited on these patterned wafers, covering the top of the dots, the bottom of the trenches between dots, and to a lesser extent, the sidewalls of the dots. The magnetic information is stored in the magnetic deposit located on top of the dots. In most of our studies, the deposited magnetic materials were (Co-Pt) multilayers with perpendicular magnetic anisotropy. The influence of the magnetic deposit in the trenches as well as on the sidewalls of the dots was investigated. Two techniques were developed to manipulate the information written on the dots. One is a thermomagnetic writing process which consists of locally heating a single dot by flowing a pulse of current from a conductive atomic force microscopy tip to the dot. The second writing technique consists of using standard write heads for hard disk to locally apply a magnetic field on each individual dot. This paper presents a review of our work on these arrays of dots made from prepatterned wafers.

Arrays of silicon lines covered by a [Co/sub 5/ /spl Aring//Pt/sub 18/ /spl Aring/] multilayer have been studied by soft X-ray Resonant Magnetic Scattering (XRMS). The magnetic peaks, which appear at the Co L/sub 3/ resonance, reveal the magnetic periodicity in the array, resulting from the magnetic coupling between the top of the lines, with a varying degree of influence from the trenches. In agreement with MFM images, the evolution of the magnetic peak intensities shows that small interline spacings and deep trenches favor antiferromagnetic order, which can be further reinforced by a specific demagnetization process.