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The thermal stability of pinned synthetic ferrimagnets with perpendicular anisotropy is investigated. These structures consist of two [Pt/Co] mutilayers (MLs) antiferromagnetically coupled through a Ru spacer, in which one of them is, in turn, exchange biased with FeMn. The switching fields of both MLs can be tuned, at a given temperature, by varying the relative number of (Pt/Co) repeats comprised in each ML. These fields are determined by the values of the exchange constant through the Ru, ARu, and the exchange constant with FeMn, Apinning. Interestingly, for some compositions, it is found that the order in which the two MLs switch during magnetization reversal changes depending on temperature. This effect is due to the different thermal evolution of ARu and Apinning.

In this work the thermal heating of tunnel junctions is investigated doing one-dimensional numerical simulations by solving the heat equation. The temperature increase is proportional to the power density jV, which is confirmed by transport measurements on patterned μm size junctions. The observed temperature increase was 2.3 K/(mW μm−2) compared to a simulation result of 0.9 K/(mW μm−2). Tunneling AFM measurements on 4, 5.4, and 6.7 A barrier half-junctions, show hot spots with current densities up to 13 times the average density value. The current concentration could explain the higher heating observed experimentally compared to the simulated value. The hot spot density is 600–900/μm2 occupying roughly 5% of the barrier surface.

Pt/Co/M sandwiches (M=Al, Ta, Cr) were prepared by sputtering. The M capping layer was oxidized either by natural oxidation in air or by exposure to an oxygen plasma. By measuring the extraordinary Hall effect in these systems, we observed that the magnetic anisotropy of the Co electrode is extremely sensitive to the degree of oxidation of the capping layer. In particular, when M=Al, the magnetic anisotropy is found in plane when the AlOx layer is under or overoxidized whereas it is out of plane when this oxide layer is stochiometric alumina. The conditions of oxidation which give the perpendicular anisotropy in Pt/Co/AlOx are found to be the same than those which lead to a maximum of specular reflection at Co/AlOx interface in Co/Ru/Co/Cu/Co/AlOx synthetic spin-valves. This crossover of anisotropy therefore provides a very useful way for controlling the oxidation of tunnel barriers. Furthermore, this phenomenon can be used to study the aging of naturally oxidized tunnel junctions exposed to air, and it i...

The effect of annealing on the structural stability of (Pt2nm/Co0.4 nm)3/IrMn7nm multilayers has been investigated using atom probe tomography. The composition of individual layers was measured after annealing at 300, 400, 500, and 700 °C. While results show that the (Pt/Co)3/IrMn stacking sequence is preserved up to 400 °C, there is an almost complete destruction of the multilayered structure when annealing at higher temperatures (500 and 700 °C). Co layers no more alternate with Pt-rich layers. The whole stack is transformed into an IrCo/PtMn bilayer. These results are interpreted on the basis of atomic mobilities and chemical affinities. Diffusion of Co and Mn is shown to become important when annealing temperature approaches 500 °C. Results are well accounted for by thermodynamics arguments considering the Co-Ir and Pt-Mn phase diagrams.

The elastic properties of sputter‐deposited Ag/Ni superlattices have been studied by means of the Brillouin light scattering technique. Measurements have been taken on both free‐standing and glass‐supported superlattices, the former deposited at 100 K, the latter at 300 K. The two effective elastic constants c11 and c44 have been determined on specimens 5 μm thick for different superlattice periods; c44 decreases by almost 40% as the bilayer periodicity decreases from 19 to 1.3 nm, while c11 shows no appreciable variation. Measurements performed on supported specimens, 0.5 μm thick, enabled us to get information also on the constant c33, which exhibits a monotonic increase with period. The elastic anomalies found can be related to the appreciable lattice distortion observed by x‐ray diffraction experiments. Both Brillouin scattering and x‐ray analysis have shown that the interface quality improves appreciably when the temperature of deposition is lowered from 300 to 100 K.

International audience; Structural investigation of Ta 3 nm / Pt 2 nm / Co 0.4 nm 3 / Pt x / IrMn 7 nm 7 / Pt 10 nm multilayers without x =0 nm and with x = 0.4 nm a Pt spacer has been performed by laser-assisted tomographic atom probe. Without a Pt spacer a strong intermixing is observed at the Co/IrMn interface. In the multilayer containing a Pt spacer the Co/Pt/IrMn interface is very weakly intermixed. It thus appears that the Pt spacer acts as a diffusion barrier that prevents the Ir and Mn atoms from diffusing into the Co layer. The consequences of this effect on the magnetic properties are discussed. The exchange bias field and the anisotropy direction of these two multilayers are analyzed and correlated with the structural investigation.

Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co/MOx interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co-O bondings at the Co/AlOx interface. (C) 2008 American Institute of Physics.

Submicron magnetic tunnel junctions exhibiting perpendicular magnetic anisotropy have been prepared by sputtering. They associate a hard and a soft electrode based on Co∕Pt multilayers, separated by an amorphous alumina barrier. The soft electrode is either free or exchange biased by an antiferromagnetic layer. The magnetoresistance ratio reaches 8% at room temperature after patterning junctions with diameter down to 200nm. The macroscopic magnetic properties were investigated by extraordinary Hall effect and conventional magnetometry measurements. The magnetic moments of both electrodes are out of plane. Two well-separated switching fields allow the realization of well-defined parallel and antiparallel configurations of the magnetizations.